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Effects of broodstock origin, rearing environment and

release method on post-stocking performance of Atlantic

salmon

Petra Rodewald

LUOVA Finnish School of Wildlife Biology, Conservation and Management

Department of Biosciences Faculty of Biological and Environmental Sciences

University of Helsinki Finland

Academic dissertation

To be presented for public examination of the Faculty of Biological and Environmental Sciences of the University of Helsinki, in the Auditorium 1041 of Biocenter 2, Viikinkaari 5,

4th of October 2013 at 12.00

Helsinki 2013

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Supervised by: Dr Heikki Hirvonen Department of Biosciences University of Helsinki, Finland Dr Pekka Hyvärinen Finnish Game and Fisheries Research Institute

Finland Thesis advisory committee: Dr Gábor Herczeg Department of Systematic Zoology and Ecology Eötvös Loránd University, Hungary Dr Ulrika Candolin Department of Biosciences University of Helsinki, Finland Reviewed by: Prof. Jörgen I. Johnsson Department of Biological and Environmental Sciences University of Gothenburg, Sweden Dr Barry Berejikian Behavioral Ecology Team NOAA Northwest Fisheries Center, USA Examined by: Prof. Neil Metcalfe Institute of Biodiversity University of Glasgow, UK Custos: Dr Perttu Seppä Department of Biosciences University of Helsinki, Finland

© Petra Rodewald (Chapters 0, II, III, IV) © Wiley-Blackwell Publishing (Chapter I) © Canadian Science Publishing (Chapter V) Cover illustration by Petra Rodewald 2013 Technical editing by Petra Rodewald ISBN 978-952-10-9051-6 (paperback) ISBN 978-952-10-9052-3 (PDF) http://ethesis.helsinki.fi Helsinki University Printing House Helsinki 2013

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CONTENTS

0 Summary

ABSTRACT ........................................................................................................................................................ 5

ACKNOWLEDGEMENTS ................................................................................................................................. 10

INTRODUCTION ............................................................................................................................................. 12

Stocking procedures .................................................................................................................................. 12

Atlantic salmon in the wild and in the hatchery: ...................................................................................... 13

Improving hatchery rearing ....................................................................................................................... 16

Release procedures ................................................................................................................................... 19

AIMS OF THE THESIS ...................................................................................................................................... 20

METHODS ...................................................................................................................................................... 22

Study area ................................................................................................................................................. 22

Study model .............................................................................................................................................. 22

Rearing conditions ..................................................................................................................................... 24

Study design .............................................................................................................................................. 24

RESULTS AND DISCUSSION ............................................................................................................................ 30

Effects of enriched rearing ........................................................................................................................ 31

Effects of broodstock origin ...................................................................................................................... 35

The benefits of the soft release ................................................................................................................ 37

Reflections ................................................................................................................................................. 37

CONCLUSIONS AND REMARKS ...................................................................................................................... 38

REFERENCES .................................................................................................................................................. 39

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ABSTRACT

Many projects today focus on the conservation of threatened animal populations or on reintroducing populations that are extinct from nature and kept alive in captivity. Post-release survival is crucial to the success of reintroduction programs. After release to the wild animals show typically maladaptive behaviour, one of the main reasons for the low survival rates after release to nature. Genetic changes in captive breeding and early rearing environment are known to influence phenotypic development of animals. The meager success of release programs are however not exclusively explained by the poor quality of the animals released. Handling and transportation to a release site represent major stressors for animals and can reduce necessary skills for survival. Methods aiming at decreasing stress before release by acclimatizing the animals to the novel environment have been developed and are used in many animal taxa. The main aim of my thesis was to investigate the effects of broodstock origin (wild vs. captive) and rearing (enriched vs. standard) on foraging, anti-predator skills, survival and migration in the wild using 1 year old juveniles and 2 year old smolts of Atlantic salmon (Salmo salar L.). I also examined the effects of stocking procedures on stress and exploratory speed of 2 year old Atlantic salmon smolts and how soft release (acclimatization after transport) methods could benefit post-release performance. In paper I, II and V salmon were reared with new enriched methods including structure and irregular changes in water level, current direction and velocity. They were reared from the age of 0+, yolk sac or eyed egg stage, respectively. Fish in paper I and II were tested in semi-natural environments. In paper I parr were examined for the effect of broodstock origin and rearing environment on foraging capacity and learning to forage on natural live prey novel to them. In paper II parr were tested for the effect of rearing environment on foraging capacity and spatial avoidance under predation risk. In paper V the effects of broodstock origin and rearing on survival and seaward migration in the wild were tested in a radio-telemetry study and compared with survival and migration of nature-caught salmon smolts. Two further studies were performed to address the effect of handling, transport and release on stress levels and, using PIT (Passive Integrated Transponder)-telemetry, exploratory speed and 24 hour acclimatization on stress indicators of smolts. Radio-telemetry was used to study the effects of a soft release method by comparing post-release migration speed and survival of soft release smolts (24 hour acclimatization after transport) and hard release smolts (directly released into the river after transportation). Enriched rearing clearly improved foraging capacity of parr and decreased maladaptive risk-taking behaviour under predation risk. The effects of origin on foraging capacity were less clear. However, offspring of wild parents started foraging earlier than fish from hatchery parents. Smolts reared in enriched tanks had a two-fold higher survival (~38% and ~19% respectively) after 290 km river migration and faster initial migration speed than standard fish. Hatchery fish with higher initial migration speed had higher probability to survive. Origin of hatchery smolts had no clear effect on survival. Nature-caught smolts

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had highest survival (~57 %). Survival chances of nature-caught smolts were independent of migration speed. Transport increased the stress indicators, and fish recovered after acclimatization, but we found no direct effect of acclimatization on survival. However, smolts explored a novel maze faster and had higher initial migration speed when the smolts had decreased stress levels before release. Smolts with initial higher migration speed had a higher probability to survive. The results suggest that the soft release method can give the smolts an initial advantage by lowering their stress levels at migration start and can hence result in an earlier start of feeding migration. These results show clearly that conventional rearing does not produce fish that are prepared for a life in the wild. The results of this study indicate that environmental enrichment can improve life skills and survival of fish significantly. This confirms a high degree of environmental plasticity in fish. Here we found no clear effect of broodstock origin. However, we tested the effects of broodstock origin only on foraging skills of 1 year old juveniles and on survival of 2 year old smolts during river migration. The influence of genetic domestication also on later life stages remains to be tested. Acclimatization (24 h) after transport proved important for lowering stress before release. The results suggests that using enriched rearing combined with soft release methods could impact the success of stocking programs for endangered Atlantic salmon conservation and additionally improve the welfare of fish reared in captivity. Keywords: Structural complexity, enriched rearing, antipredator response, post-release performance, hatchery supplementation, Atlantic salmon, survival, foraging, stocking success, telemetry, stress response, cortisol, glucose, lactate, PIT-technology, phenotypic plasticity

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This thesis is based on the following papers, which are referred to in the text by their Roman numerals: I Rodewald P., Hyvärinen P. & Hirvonen H. 2011. Wild origin and enriched environment

promote foraging rate and learning to forage on natural prey of captive reared Atlantic salmon parr. - Ecology of Freshwater Fish 20, 569-579.

II Rodewald, P. Hyvärinen P. & Hirvonen H. 2013. Enriched rearing promotes foraging

rate and decreases risk-taking under predation threat in Atlantic salmon parr. - Manuscript.

III Rodewald P., Vainikka A., Hyvärinen P. & Hirvonen H. 2013. Effects of handling and

transport on the blood glucose, plasma cortisol and lactate concentrations of Atlantic salmon (Salmo salar) smolts. – Manuscript.

IV Rodewald P., Hyvärinen P., Vainikka A., Laaksonen T. & Hirvonen H. 2013. An

assessment of the benefits of soft vs. hard release of Atlantic salmon smolts. – Manuscript.

V Hyvärinen P. & Rodewald P. 2013. Enriched rearing improves survival of hatchery

reared Atlantic salmon smolts during migration in the River Tornionjoki. – Canadian Journal of Fisheries and Aquatic Sciences Doi: 10.1139/cjfas-2013-0147

AUTHOR’S CONTRIBUTION

This thesis is part of the cooperation between the Integrative Ecology Unit (IEU), University of Helsinki (UH) and the Finnish Game and Fisheries Research Institute (FGFRI), Kainuu. All enriched rearing methods were developed in cooperation by Heikki Hirvonen (HH), Pekka Hyvärinen (PH), Ari Leinonen and Pekka Korhonen at the Kainuu Research station in Paltamo, Finland. Original study ideas in papers I-IV were developed by Heikki Hirvonen and Pekka Hyvärinen. Experiments were designed in cooperation by HH, PH and Petra Rodewald (PR) in paper I and II. In paper III and IV the experiments were designed by HH, PH, PR and Anssi Vainikka (AV) from the University of Oulu and the University of Eastern Finland. PH and PR designed the experiment in paper V and Panu Orell and Atso Romakkaniemi from the FGFRI were helping during the planning phase of study V. I PR and PH were responsible for the data collection and were assisted by the master

students Elias Hämäläinen and Markus Haveri from the University of Helsinki and by the technical assistant Eliisa Rantanen (ER) from the FGFRI. PR and HH were responsible for statistical analysis. PR, PH and HH were responsible for preparing the article.

II PR and PH were responsible for the data collection with the help of Jouko Moilanen

and ER from the FGFRI. PH was the main responsible for the PIT-data collection and analyses. PR and HH were responsible for the statistical analysis and PR, HH and PH for preparing the manuscript.

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III PR and AV had the principal responsibility for the data collection, in assistance with

PH and the trainee Sarah Neggazi (SN). AV, HH and PR had the principal responsibility for the statistical analysis. PR and AV were responsible authors and HH and PH helped preparing the manuscript.

IV PH, PR, AV and Tapio Laaksonen (TL) were responsible for the data collection and SN

was assisting during the stress experiment. PH was the main responsible for the telemetry study and PR for the collection and analysis of the PIT-data. AV, HH and PR were responsible for the statistical analyses. PR, PH, HH and AV prepared the manuscript.

V PH and PR had the main responsibility for the field work, in assistance with Olli van

der Meer from Tmi Olli van der Meer and TL, Rauno Hokki, Ville Vähä and Mikko Jaukkuri from the FGFRI. PH had the main responsibility for the radio-data collection and analysis. PH and PR were responsible for the statistical analysis and preparing the manuscript.

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ACKNOWLEDGEMENTS

Siellä on kirppuja, luteita, täitä….thanks to the forests and lakes of Kainuu that were giving me shelter during the field studies and during preparing my thesis summary. The silence of the nature and its people therein was extremely helpful during this process. It is here I discovered the dialog with myself… As the time for the defense closes by I am heading retro, sitting with the tiny antique writing table from which the white painting has started flaking off a long time ago, looking out of the window in front of it. White curtains are framing my view to the forest, lying snow white and quiet in the winter sun. I have been sitting here many times before the last years; it has become dear and familiar to me now. I do not feel stress. I enjoy bringing the work of the past years finally to paper (computer). I hope that others might have use for it and might even enjoy reading it. My thoughts go to my son Tobias, my sweet little sweet teenage rebel. “Du min eneste sønn, du er det aller kjæreste i mitt liv. Jeg elsker deg!” Tobias has not exactly helped me writing my thesis. He has, however, done a great job helping with the experiments. When the other children went to their summer holidays in the south, he headed eastwards to defeat the wild rivers and lakes of the north and to track down and capture monstrous fish with teeth as large and sharp as razor blades. But mostly he helped focusing on important things in life. He made me burst in laughter with his crazy boyish ways and ideas. He made my heart beat up in joy when talking about the things he burns for. “Eg veit ikkje kva det vil bli av deg seinare i livet, men at det blir noko spesielt det er eg sikker på.” I think of what I have already achieved, not what I still have to achieve. The deadline for the thesis delivery is not THE critical deadline in life, there is a life after the PhD and, by the way I created this deadline myself. And thinking of deadlines, I here want to thank my supervisors Heikki and Pekka for not ever giving me any deadlines, but for letting me work freely as every mother being should be allowed to and kiitos kärsivällisyydestä ja luottamuksesta. I am very proud of the work we did together! To my favourite coordinator ever, Anni kiitos, sinulla on uskollisuuteni ikuisesti. Kiitos Anssi! No stress never no more! I also want to thank the members of my thesis committee Gabor and Ulrika for their support during the years! To my fellow compassionates, thank you for moral support during these years: Kiitos, Jussi, moimoimoi: Meine liebe Christina, ich hoffe wir werden auch noch weitherhin zusammen auf Tischen tanzen. Abilash and Bineet (our very own Panda), Alexandre, Martina, Eva, Anton, Jacky and all my other colleague students who have been or are still sweating over their theses, hold out. Thanks also to all the members that make NoWPaS a memorable event every year! To Markus and Elias for giving me a truly unforgettable first summer at the Research station in Paltamo. Thanks to the staff at the Paltamo Research station. Kiitos pomo and field-friend Olli van der Meer. To Barry and Jörgen, you cannot imagine how much your very good and nice comments encouraged and motivated me in the final sprint of my thesis finalization, thank you! Thanks to family and friends, who always asked the same question; are you fin(n)ish(ed) now? My most special friends in Norway Anja, Laura, Patricia and Solveig. Kiitos ensimäinen suomalaista ystävän Heli (and Piet), who actually became my friend before I arrived in Finland, on the famous ferry-trip Stockholm-Helsinki. My grandmother pushed me into education, but rather wanted me to become a physician: “What are you doing in that terrible Finland. They eat bread made from trees. Come back home!” My father, who pins little flags on his map to mark where his

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daughter is at every moment. Bruderherz und Schwiegerschwesterherz, ich bin froh, daß es euch gibt! Sindre, takk, for alltid å ringde for å høre kor det går og for nyhetene fra gamle landet. Thanks to the dogs, you are neither nice nor evil; you helped me to focus on the important things in life and forced me to take a break in nature every day. You are therapy! Whether animal or human, thanks to all that contributed to the finalization of this thesis directly or indirectly! And finally to my dearest friend and companion, Pekka, I could never have done this without the loving support from you and your family. You had to stand most of the frustration during these years (mä olin häirikkö); the despair, the disappointment over rejected papers (haistakaa!), but you only responded with understanding and patience, I will always be grateful! It is true there were some tears, but what I will remember most during this period are the happy times when things went well; like how glad I was when people like my talks at conferences and workshops, how motivating conferences are and all the great people I met there, all the nice people I met during the experiments and travels, dinners and celebrations at the university with my fellow students, midsummer night at the Paltamo research station, midsummer night on the shore of the Tornionjoki river, papers that were accepted and the wonderful celebrations of the same. Summa summarum it has been a great time Now this is done and new adventures are waiting! Snipp snapp snute, thank you for now… This thesis was funded by the Tor and Maj Nessling foundation and the Finnish Cultural foundation. Thanks for the trust you put in our project.

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INTRODUCTION

In my thesis I investigate factors that are important for conservation stocking. The

current methods used for production and release of fish are not optimal and I wish to

contribute with possible solutions and inspire future research on the issues needed for

conservation of our fish populations. In this thesis I will first examine the effects of

broodstock origin and early environmental conditions on phenotypic development of

Atlantic salmon. My main focus is how broodstock origin and structural complexity

combined with variation in the rearing environment affect foraging, risk-taking under

predation threat and survival. Second, I address the effects of handling and release

procedures. These are known to be stressful events for fish and I investigate their effect

on stress indicators and survival after release.

My thesis will contribute to the current knowledge of heritable and environmental

effects on phenotypic development and widen the understanding of how stress affects

post-release performance. My findings can prove useful for the development of

husbandry and stocking practices to increase the welfare of fish kept in captivity and

survival chances of hatchery fish released into the wild.

Stocking procedures

Stocking of hatchery reared fish has been widely used as a management tool in

supplementation, reintroduction, for mitigation of populations that are threatened due

to human activities, but also for enhancement to increase the yields of healthy

populations and for the introduction of alien species to establish new fisheries and for

sea ranching (Cowx 1994; Bell et al. 2008). High numbers of fish are annually released

into nature. In Finland alone 1.189.000 salmon smolts were released in 2011 (ICES 2012).

Stocking has prevented extinction in some populations (e.g. Carmona-Catot et al. 2012)

and many fisheries would likely collapse without stock enhancement programs (Cowx et

al. 2012). Despite of the high stocking efforts stock assessments report decreases of

recapture rate over time (e.g. ICES 2012). The rearing of fish in hatcheries is costly and

makes stocking an expensive management tool (Cowx et al. 2012). In addition, it is

unethically to continue releases of hatchery fish into nature well-knowing that they will

most probably die soon after release (Brown & Day 2002). To increase the benefits of

releases, to make them more cost efficient and ethically defendable, we have to identify

the controlling mechanisms for these failures and develop new procedures to increase

the success of stocking programs.

Many and likely additive factors are causing the low success of many stocking programs,

but one of the most important ones is the high mortality of hatchery fish after release

(Kristiansen et al. 2000; Romakkaniemi 2008). One important factor for the low survival

of hatchery fish in the wild is that fish from threatened or extinct populations are taken

to captivity. A life in captivity inevitably leads to adaptation to the artificial environment

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(domestication). Genetic changes can occur over generations and the unnatural rearing

environment in captivity prevents the fish from expressing and developing their natural

behaviour. This produces fish that differ genetically and phenotypical from fish in wild

populations. Hatchery fish are consequently poorly adapted to a life in the wild

(Huntingford 2004). Releasing unprepared fish into the wild and rearing fish in

environments where they are unable to express natural behaviour are welfare concerns

as well. Another factor causing welfare issues and potentially high mortality of hatchery

fish after release, are stocking procedures that often neglect detrimental consequences

of stocking stress like handling, transport and release (Cowx et al. 2012).

Atlantic salmon in the wild and in the hatchery: Mechanisms creating

differences between wild and hatchery fish

Domestication

Genetic changes and loss of genetic diversity due to adaptation to captivity, genetic drift,

inbreeding and relaxed selection occur over generations and can result in reduced fitness

under natural conditions (Ford 2002; Araki et al. 2007; Frankham 2005, 2008, 2010). The

hatchery selection favours fish that are well adapted to captivity, but maladapted to the

wild (e.g. Christie et al. 2012), leading to differences in behaviour, physiology and survival

between wild and hatchery stocks. Information on long-term impacts of genetic variation

losses on extinction risk is still scarce. Araki et al. (2007) showed a ~40% decline in

reproductive success for each generation in captivity when released to nature and it has

been shown that the success of stocking is negatively related to the time spent in

captivity (e.g. Romakkaniemi 2008). Studies on many fish species, including Atlantic

salmon, have found genetic difference between farmed and wild fish (e.g. Allendorf &

Phelps 1980; Verspoor 1988; Säisä et al. 2003; Mjølnerød et al. 2004; Liu et al. 2005;

Vuorinen 2006). Most of these studies report a loss of genetic variability probably due to

genetic drift. Breeding systems for the genetic management of species that are desired

to conserve are widely ignored (Frankham 2010). We are lacking important knowledge of

the link between molecular variation and fitness parameters (Frankham 2010; Cowx et al.

2012) in order to optimize procedures for practical management. There is, however, little

evidence that genetic domestication results in complete loss of the behavioural

repertoire, as even hatchery fish are able to learn foraging on novel prey and they can

learn how to escape predators. How much of the behavioural repertoire is lost, probably

depends on the length and type of domestication. This indicates that it is largely a change

in response threshold that explains the differences between wild and captive animals

(Price 1999). Some of which could be counteracted to a certain degree by improving

husbandry practices. It has been shown that fish can be reared in hatcheries and express

similar levels of survival after release to nature as their wild conspecifics, but this is

highly depended on hatchery practices (e.g. Thériault et al. 2010; Moore et al. 2012).

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Conventional rearing environments are lacking natural key stimuli important for the

development of natural behaviour. Hatchery fish are typically grown in static, featureless

environments at unnaturally high densities. Fish are provided an excess of pellet food,

preventing them to learn how to capture natural live prey. Wild fish live in complex

environments and learn by experience how to capture and handle various live prey types

(Sundström & Johnsson 2001). The hatchery environment provides no structure or

shelter. Sheltering is an important predator defense and it has been shown that adding

shelter to the rearing environment can decrease metabolic demands and stress levels

(Millidine et al. 2006; Näslund et al. 2013). Predators are lacking and the fish never learn

how to apply proper antipredator behaviour. In addition, variation and fluctuations

found in the wild may greatly influence fish development, but are today ignored in the

hatcheries (e.g. Olla et al. 1998; Huntingford 2004). In nature fish have to adapt from the

beginning to changing conditions like periods with high currents and low currents caused

by for example spring floods and droughts. Also the food supply in nature varies, prey

availability and composition in the wild changes annually, seasonally and even daily and

spatially. Additionally, wild fish have to make a trade-off between foraging and predator

defense depending on the presence or absence of predators (Lima & Dill 1990). Under

natural conditions these factors would select for phenotypes that are able to adapt to

natural conditions in the wild and induce natural selection for certain behavioural traits

in a population. The lack of variation in the hatchery results in the production of fish

expressing little flexible behaviour and that cope scarcely to the conditions in the wild.

Implications of domestication for foraging skills

Foraging skills have an inherited component, but are also relying on experience to

become fully developed (Hughes et al. 1992; Warburton 2003; Huntingford 2004).

Previous studies have shown that learning is crucial for fish to fine-tune foraging skills

(Kieffer & Colgan 1992; Reiriz et al. 1998; Warburton 2003). In the hatchery modest

foraging skills are needed to consume large amounts of pellets with little effort.

Additionally, different foraging skills are required to forage on pellets vs. foraging on live

prey, thus giving the fish little chance to develop natural foraging behaviour (Olla et al.

1998; Brown & Day 2002). When released into the wild the fish have difficulties to start

feeding on natural live prey. Hatchery reared fish have lower feeding rates, forage on

fewer prey types and are slower to switch between prey types compared to their wild

conspecifics (Sosiak et al. 1979; Ersbak & Hase 1983; Kristiansen & Svåsand 1992; Ellis et

al. 2002; Vehanen et al. 2009; Larsson et al. 2011). Hatchery fish have even shown to

forage on stones, leaves and pebbles (Ellis et al. 2002). As a consequence hatchery reared

salmon parr have shown to suffer a decrease in their condition factor when switching

from pellets to a live prey diet (Costas et al. 2013), which can explain the depressed

growth rates upon release when compared to wild fish (Olla et al. 1998). These

differences seem to continue throughout live, as evident from stable isotope sampling

also at the marine stage of Steelhead salmon (Oncorhynchus mykiss, Quinn et al. 2012).

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Steingrund & Fernö (1997) found that Atlantic cod (Gadus morhua) reared on a pellet

diet learned to forage on live prey, but were less efficient than wild cod. Hatchery reared

fish are often found to feed in an energetically costly position close to the surface (Furuta

1996; Stunz et al. 2001), which increases their susceptibility to predators. They often

cease foraging for an extended time period after release (Miller 1954; Paszkowski & Olla

1985; Usher et al. 1991), probably because they are unable to handle the novel prey. For

example, Sundström & Johnsson (2001) showed that wild-caught brown trout (Salmo

trutta) were more efficient in handling a novel prey and had a 75% higher foraging rate

than hatchery reared trout. However, hatchery fish can also become as efficient foragers

as their wild conspecifics after an initial learning period (Johnsen & Ugedal 1989;

Kristiansen & Svåsand 1992; Reiriz et al. 1998; Sundstöm & Johnsson 2001). This learning

phase causes nevertheless a delay in foraging after release. Whether or not this could

influence the energy household negatively has yet to be investigated, but it could

theoretically have implications for antipredator behaviour, as hungry fish seem to take

greater risks under predation threat than satisfied fish (e.g. Hossain et al. 2002).

Implications of domestication for antipredator skills

Predation is a powerful selective force, as individuals with poor skills will likely be eaten.

Applying appropriate anti-predator behaviour is obviously crucial for survival in nature. It

is therefore not surprising that antipredator behaviour has a strong inherited component

(Magurran 1990; Kelley & Magurran 2003). Laboratory studies have shown that young

predator-naïve salmonids have an innate ability to recognize the odor of certain

piscivorous fish-predator species (Hirvonen et al. 2000; Berejikian et al. 2003; Hawkins et

al. 2007). This has not yet been evident for piscivorous mammals (Roberts & Garcia de

Leaniz 2011). Other studies have shown that fish have innate abilities to recognize

predators visually, but have to learn about the chemical cues by experience (Magurran

1989; Utne-Palm 2001). However, most of the studies are using dummy models or

chemical cues and measure recognition of a predator threat as a behavioural response

like area avoidance, freeze or flight. In the wild hatchery reared fish do not only have to

recognize the predation threat and freeze or escape, but the antipredator tactic has to be

appropriately applied to avoid being eaten. For example, juvenile Atlantic salmon escape

or freezes under predation threat, but farmed fish start activity sooner after an attack

(Einum & Fleming 1997; Fleming & Einum 1997). It has also been shown that the

swimming speed and duration of wild fish is superior over that of hatchery fish (e.g.

Rimmer et al. 1985; Basaran et al. 2007). This can influence their ability to catch prey and

escape predators, but swimming abilities are also required for navigation and speed

during migration. Many studies have shown that if prey fish survive an encounter with a

predator they will also have a higher probability to survive next time (Dill 1974;

Berejikian 1995; Hossain et al. 2002). Numerous studies have shown that hatchery reared

fish fail to apply appropriate antipredator responses (e.g. Brown & Smith 1998; Nødtvedt

et al. 1999; Berejikian 1995; Berejikian et al. 1999; Meager et al. 2011; Benhaïm et al.

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2012) or they lack cryptic abilities like burying skills and camouflage coloration (e.g.

Maynard et al. 1996; Fairchild & Howell 2004). Predator-naïve hatchery-reared Atlantic

cod (Gadus morhus) are more active (increasing susceptibility to predators) and keep

initial shorter distances to the predator than wild cod. Wild cod were also inspecting the

predator twice as often as the hatchery cod (Nødtvedt et al. 1999). Hatchery reared fish

might be slower to realize the full extent of the threat, as domesticated Atlantic salmon

have shown to display different responses to a possible predation threat in terms of less

pronounced heart responses and flights (Johnsson et al. 2001) and delayed

hyperventilation peaks compared with wild conspecifics (Hawkins et al. 2004).

Implications of domestication for survival

Survival rates in many stocking programs are low for newly released hatchery reared fish

(e.g. Svåsand & Kristiansen 1990; Tsukamoto et al. 1997). Studies have shown higher

survival for wild fish than released farmed fish (up to 4.5 times higher for wild Atlantic

salmon, Saloniemi et al. 2004; Romakkaniemi 2008), often caused by predation (e.g.

Larsson 1985; Jepsen et al. 2000; Kekäläinen et al. 2008). However, it has also been

shown that the parasite and disease resistance is often higher in wild fish which can likely

affect survival of hatchery fish after release to the wild (Hemmingsen et al. 1986; Johnsen

& Jensen 1991). There is a large gap of knowledge in how species differ in their

adaptation to the captive environment and how genotype and environment interact in

development of the phenotype. However, we know that captivity is favouring individuals

that would probably not have survived in the wild. The selection intensity is also much

stronger in the wild; only about 1-5 % of the hatched salmon might survive their first

summer (Elliott 1994) compared to about 90 % of fish surviving the first summer from

start feeding in the hatchery (paper V). Thus adaptation to captivity should impact

survival after release to the wild (Frankham 2008).

Improving hatchery rearing

The use of wild parents as broodstocks

To date it is recommended to maintain genetic diversity and minimize inbreeding

(Frankham 2010). In practice this means to minimize generations in captivity by using

wild parental broodstocks and to avoid outbreeding depression which could eventually

lead to a loss of the local adaptation and effect reproductive fitness (Frankham 2005). In

some areas, e.g. in the Swedish Rivers Umeälven, Ljusnan and Dalälven wild parental

broodstocks are used to breed fish for stocking purposes (ICES 2012), but the use of wild

parental broodstocks are today largely ignored by stocking programs (reviewed in Cowx

et al. 2012; Frankham et al. 2010). It is recommended to take individuals for the

broodstock from (a) the water body to be stocked. In the cases of populations that are

extinct from nature or have a small populations size one could use (b) a donor stock with

the same biological characteristics as the recipient system, e.g. from neighboring streams

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or lakes or (c) a population from a water body with similar environmental characteristics

or (d) using a large number of individuals in an attempt to assure adaptive genetic

variation (Cowx 1994; Cowx et al. 2012). However, the mechanisms in captive breeding

are often poorly understood. For example, using high numbers of fish does not

necessarily prevent loss of genetic diversity, as differential mortality will produce fish

that are well adapted to the hatchery, while fish that would adapt well to natural

conditions are lost through hatchery selection. In this way we can unintentionally select

for many fish with undesirable traits (Araki et al. 2007) as we are lacking sufficient

knowledge to predict what is selected for in the hatchery.

Enriched rearing

So, how to overcome deficits in hatchery reared fish? Nowadays the production of fish

aims at high numbers rather than considering natural ecological and behavioural needs

of the animals (Brown & Day 2002). In order to produce fish that look and behave more

wild-like we have to integrate more of the natural conditions into our rearing. But first

we have to learn more about how development in fish is generated. During ontogeny the

nervous system in the brain parts responsible for learning are modified by experience,

different stimuli are resulting in expression of different behaviours (Marcotte &

Browman 1986). Environments with higher degrees of complexity shape fish with a wider

repertoire of complex behaviour. This generates fish with higher learning capacities that

are likely to adapt faster to changing conditions (Odling-Smee & Braithwaite 2003).

Behaviourally flexible fish are expected to have higher survival chances in new

environments (Salvanes & Braithwaite 2005). Improving the rearing environment of

hatchery reared fish destined for release into the wild is still largely ignored in the

hatcheries even though it has shown benefits in captive rearing for conservation in e.g.

mammals (e.g. Rosenzweig & Bennett 1996; Roth & Dicke 2005), birds (e.g. Rosenzweig

& Bennett 1996; Krause et al. 2006) and reptiles (e.g. Wheler & Fa 1995; Case et al.

2005). There is now extensive literature on fish indicating that more complex rearing

environments promote the development of fish brains (Kishlinger & Nevitt 2006; Näslund

et al. 2012), cognitive abilities (Brown et al. 2003; Kotrschal & Taborsky 2010; Strand et

al. 2010), behaviour (e.g. Berejikian et al. 1999; Braithwaite & Salvanes 2005; Salvanes &

Braithwaite 2005; Salvanes et al. 2007; Moberg et al. 2011; Roberts et al. 2011) and

survival in the wild (Maynard et al. 1996). These studies have revealed that behavioural

and neural plasticity and the development of cognitive abilities are influenced positively

by increasing the complexity of the nursing environment (see van Praag et al. 2000 for a

review).

Taken together, these studies demonstrate that it is possible to alter fish behaviour by

manipulating the rearing environment. But we are still lacking information about when to

start enriched rearing and how. Not all size fits all and not all species or populations

benefit from the same methods. Modifications of the rearing environment should be

18

species specific, tested and adjusted to individual needs. For doing this one has to

consider the natural ecology and behaviour of the species in question. For example,

juvenile Atlantic salmon prefer higher current speed than juvenile Brown trout

(Armstrong et al. 2003) and occupy gravel bottom close to large boulders in the wild

(Keenleyside & Yamamoto 1962) while common carp thrives among submerged wood

and aquatic vegetation (Jones & Stuart 2007). To enable fish to develop and express their

natural behaviour we have to find ways to simulate natural conditions and we have to

test whether the applied methods have the desired effect.

Additionally, fish have to be subjected to variation in the rearing environment in order to

develop adaptive behaviour (Ebbesson & Braithwaite 2012). Swimming training is

increasing swimming performance (Farrell et al. 1990; Anttila et al. 2006) and swimming

performance is important for foraging, predators defence and for feeding migrations. It

has been shown that hatchery rearing reduces flight response behaviour (Meager et al.

2011; Benhaïm et al. 2012). Meager et al. (2011) showed that wild caught Atlantic cod

(Gadus morhua) were faster in turning and were turning at larger angles during escapes

from a possible predation threat than predator naïve hatchery cod. Benhaïm et al. (2012)

found that wild caught sea bass (Dicentrarchus labrax) escaped a predator threat at

higher angular velocity and distance from a stimuli point than domesticated sea bass. The

most likely explanation for these differences is that the escape response of wild fish was

shaped by experience with a predator, while hatchery reared fish had no previous

experience with predators (Meager et al. 2011). Atlantic salmon parr are drift feeders,

positioning themselves on the bottom to occasionally dart towards the surface to snatch

insect prey. It has been shown that hatchery Atlantic salmon utilizes slower water

currents than their wild conspecifics and this can lead to lost feeding opportunities

because they will encounter less prey at lower current velocities. The preference to stay

in slower water currents of hatchery salmon, might be connected to swimming and

migration ability, as hatchery reared Atlantic salmon have shown decreased swimming

abilities compared with wild conspecifics (Anttila & Mänttäri 2009). Swimming training in

the hatcheries could potentially counteract some of the swimming deficiencies (Farrell et

al. 1990; Antilla et al. 2006, 2010), but swimming training programs are only efficient if

the proper exercise program is applied (Anttila et al. 2006). However, their methods

worked in a laboratory setting, but after release to the wild, trained fish were actually

migrating slower than standard hatchery and wild smolts (Anttilla et al. 2011).

However, these methods have so far been largely been tested at laboratory scales, which

are not applicable to a real production scale scenario and few studies have to date

(Maynard et al. 1996) shown survival advantages of fish reared with enriched methods.

Therefore we developed an enriched rearing method that was easily applicable to real

scale production and with simple methods that were aiming at mimicking the features of

a natural environment.

19

No study has to date shown the effect of domestication, enriched rearing and their

interaction on survival skills and survival. To gain a picture of what influence broodstock

origin and rearing environment had on the development of fish behaviour and life skills,

we had to disentangle the origin from the rearing effect. We achieved this by rearing the

offspring of either wild-caught parents or parents from a broodstock that had been held

in captivity for generations with either a standard or an enriched rearing method. In this

way we could test the origin effect and the rearing effect simultaneously.

Release procedures

However, environmental enrichment might not be sufficient for improving post-release

performance of fish. Release procedures, have shown to be crucial when introducing

other captive animal taxa to the wild (Teixeira et al. 2007). In the past fish have been

released without further thoughts of release methods. Domesticated fish were simply

flushed into the natural recipient without considering that the fish were not adapted to

these systems and had very small chances to survive. This is still common procedure for

many fish species, even though our knowledge about biological and ecological

requirements of different species is increasing. We are also aware about factors

contributing to the failure of many releases. Prior to release animals have to be caught

from e.g. rearing tanks. They have to face handling, transport and the release into a

novel environment (Teixeira et al. 2007). This leads to elevated stress levels. The fish are

then released into the novel environment while likely still impaired by handling and

transport stress. Experiments on different fish species have shown that stressors like

these result in elevated stress levels that will take 24 hours or more to return to baseline

levels (e.g. Schreck et al. 1995; Iversen et al. 1998; Hyvärinen et al. 2004). Literature

shows that after netting and transport a peak in cortisol levels usually occurs 30-60

minutes post-stressor, with a delayed peak of 1-2 hours for lactate and glucose (e.g.

Bonga 1997; Finstad et al. 2003; Hyvärinen et al. 2004). Hyvärinen et al. (2008) found in

pike-perch that size affected stress levels and mortality with larger fish having decreased

plasma cortisol and better survival. The fish would most likely benefit by decreasing

these stress levels before release, by acclimatizing them to the release area (Teixeira et

al. 2007). But there are additional reasons why fish should be acclimatized before

release. For example cultured winter flounder (Pseudopleuronectes americanus) have

poorly developed cryptic abilities. These do, however, increase over time. Fairchild &

Howell (2004) found that cultured sediment-naïve winter flounders needed a minimum

of two days to improve their burying skills. Furthermore, they needed 90 days to match

their color to the sediment. They were also more vulnerable to bird predation, which

could be connected with increased susceptibility due to the color-mismatch to the

sediment. In this example the fish might benefit from an adaptation period sheltered

from predation risk in a so-called soft release (Fairchild & Howell 2004).

20

Mortality after release is especially high immediately after release, often because of high

predation, but could also be connected to increased stress levels. Increased stress levels

can affect cognitive abilities (Wood et al. 2011), resulting in loss of learnt behaviour.

Hatchery reared fish have intentionally and unintentionally been selected for high

growth rate, which has lately been connected to a shorter memory duration, so maybe

they also simply forget fast what they have learned (Brown et al. 2011). New release

methods are currently under development and are tested for different species of fish.

These involve letting the fish acclimatize in e.g. predator free net pens or ponds in the

release area. The idea is that fish get the chance to recover from the stressful transport

and get familiar with the environment in which they are going to be released. It gives

them for example the opportunity to learn foraging on novel live prey or to get the first

contact with predators, but without getting eaten. However, prolonged times in

acclimatization compartments should also be avoided as it has shown to attract

predators (Fairchild et al. 2008). If predators wait in front of the acclimatization

compartments the fish meant for release might habituate to the predator smell and fail

to recognize them as a threat after release (Berejikian et al. 1997; Jachner 1997). Piscine

mammal, bird and fish predators can also attack fish inside the acclimatization

compartments and either kill, hurt and/or stress fish through net-pens or from above.

The acclimatization area has to be secured accordingly to the predation pressure in the

area (birds, mink etc.). Fish (e.g. salmon smolts that are eager to start migration) can also

become stressed when kept too long at the release site and this can result in increased

scale damage, fin erosion and injuries at high densities in cages and net-pens (reviewed

in Latremouille 2003; Jonsson & Jonsson 2009). Many of the studies employing soft

release methods are not showing the desired effect (Kenaston et al. 2001; Thorfve 2002),

but others report good results (e.g. Cresswell & Williams 1983; Finstad et al. 2003; Baer

& Brinker 2008). Extensive planning, including pre-trials, is crucial to determine the

appropriate acclimatization time and procedure for the population in question.

AIMS OF THE THESIS

The overall aim of my thesis was two-fold. First I wanted to investigate if using wild

caught parents as broodstocks combined with enriched rearing environments have the

potential to improve survival skills of hatchery fish reared for stocking purposes.

Ultimately, if survival of smolts of wild origin reared with enriched methods would

increase after release into nature. Second, I was interested in how soft release methods

could be beneficial for stocking of salmon smolts. Answering these questions could

contribute to the development of methods that increases post-release performance and

survival of hatchery fish.

21

Genetic domestication and unnatural rearing environments of hatchery fish are

considered to be key factors in the development of phenotypes that are maladaptive in

the wild. There is a high risk for genetic diversification between wild and farmed salmon.

However, salmon express high degrees of phenotypic plasticity and can adapt to the

rearing environment both physiologically and behaviorally. Thus the rearing environment

can have profound effects on physiology, behaviour and survival in the wild. Knowledge

about the effects of rearing-environment and genotype on development of salmon

phenotype and consequent survival is scarce and remains largely untested. I therefore

tested the prediction that:

1) Salmon parr of wild origin reared in an environment with structure and changing

water current direction and velocities will develop adaptive behaviour. This will be

expressed in foraging capacity and learning to forage on novel life prey and

reduced maladaptive risk-taking behaviour under predation risk in terms of prey

intake and avoidance.

Handling, transport and release into a novel environment are stressful events for fish.

Stress can impair physiological performance and disease resistance. Additionally, stress

can alter fish cognition and behaviour, taking attention away from applying behaviour

that is important for survival after release. Therefore fish have to be given an adequate

acclimatization period before release (soft release). I predicted that:

2) Salmon smolts released with a soft release method will have lower stress levels,

start migration earlier, and have higher migration speed and higher survival

compared with directly released smolts.

Using wild origin broodstock in combination with an enriched rearing method will shape

fish with adaptive behaviour. Soft release methods give an initial advantage in terms of

lowered stress before release. Combined this will lead to increased survival chances. I

tested the prediction:

22

3) Salmon smolts of wild origin reared in an environment with structure and

changing water current direction and velocities will develop adaptive behaviour

and survive better in the wild given the adequate time to rest before release.

METHODS

Study area

The foraging and behavioural studies in paper I, II and IV, as well as the stress indication

studies in paper III and IV were conducted at the Kainuu Fisheries Research, Finnish

Game and Fisheries Research Institute’s (FGFRI) research station in Paltamo

(64° 23' 20" N 27° 30' 23" E, Fig. 1). The telemetry study in paper IV was performed in the

River Varisjoki (64° 23' 20" N 27° 30' 23" E). The Varisjoki (mean annual discharge 4.6

m³/s) has been known to support salmon smolt production in old times. It is part of the

River Oulujoki watercourse (65° 01' N, 25° 30' E). The Oulujoki watercourse includes small

unregulated rivers like the Varisjoki that discharges to the Baltic Sea via the Lake

Oulujärvi (surface area 918 km2) and the River Oulujoki. The River Oulujoki was one of

the most important smolt production areas of Atlantic salmon of the Finnish Baltic Sea

coast. During the 1940-1950 extensive building of power plants in its watercourse lead

finally to the extinction of the local wild Atlantic salmon population. The telemetry study

described in paper V was performed in the River Tornionjoki (67° 57' 00" N 23° 41' 00 "

E). The Tornionjoki (mean discharge 400 m3/s) is the largest unregulated river system in

Western Europe and the northernmost River of the Baltic Sea. It has one of the world’s

largest spawning areas for Atlantic salmon and is producing more wild salmon than any

other population in the Baltic Sea, with a smolt abundance of over 1 million individuals

annually and a record catch of 122000kg in 2012 (Romakkaniemi 2008; Vähä et al. 2013).

Study model

The studies were carried out using hatchery reared Atlantic salmon parr and smolts from

three Baltic populations. We used offspring of either wild naturally spawning parents or

hatchery parents from the river populations Simojoki in paper I and from the Tornionjoki

population in paper II and V. In paper I the parr were offspring of wild-caught parents or

offspring of 2nd or 3rd generation hatchery parents. We only have the genetic data from

Simojoki parr that were reared in the same tanks as the experimental fish. DNA-analyses

using 14 microsatellite loci showed that the genetic variability was lower among offspring

of hatchery parents compared to offspring of wild parent. The internal relatedness (IR) of

the hatchery offspring was higher as was the locus adjusted homozygosity (HL). The

23

Figure 1 Map of study locations and picture of the Paltamo Research station with the Varisjoki situated to the left of the station. The location of the research station and the Tornionjoki are marked on the map with asterisks.

latter was 20% higher in the hatchery offspring. Using 14 markers, the average number of

alleles of the wild offspring was 8.0 and for hatchery offspring 6.2. Thirty three families

were found among the hatchery offspring with an average family size of 3.3. There were

43 families in the offspring of wild parents and the average family size was 2.4. In paper V

the smolts were offspring of either wild-caught parents or 3rd or 4th generation hatchery

fish. The Simojoki and the Tornionjoki are the last Finnish salmon rivers that still have

original natural reproducing populations, but they have also been taken into captive

rearing to support stocking in other Finnish rivers where the local populations have gone

extinct. We chose these populations for three reasons. Firstly because we could utilize

wild caught fish as well as captive reared parents as a broodstock to study the effect of

domestication and environment simultaneously. Second, the River Tornionjoki is

unregulated, thus migration behaviour and survival towards the sea could be studied.

And third the present plan is to reintroduce Finnish salmon populations. For this it is

planned to use the Tornionjoki population as a broodstock for some of those populations

that have gone extinct from their natal rivers (Erkinaro et al. 2011). In paper III and IV we

used smolts from the River Oulujoki population. This population has gone extinct from

nature and has since the 1950s been hold in captivity. We chose the Oulujoki population

for these studies because there are current plans in progress to restore the natural

habitat in these areas and to open migration highways descending into the Baltic Sea to

recover a self sustaining Oulujoki population. After keeping this population in captivity

for more than six centuries, it is important to test if these fish can survive on their way to

the feeding grounds in the Baltic Sea. No studies on stress indicators have been

performed for this population before and as stress responsiveness and copying can differ

substantially between populations (Barton 2000), we had, in order to determine a soft

release procedure, to find the adequate recovery time for fish from this population.

24

Rearing conditions

All fish were reared at the Kainuu Fisheries Research, FGFRI’s research station in Paltamo.

Standard fish were reared following the methods of Det Norske Veritas Quality system

certificate no. 2000-HEL-AQ-833, SFS-EN ISO 9001. The enriched rearing methods were

continuously developed during my study period. The rearing methods for the Simojoki

and the Tornionjoki were therefore slightly different. Enriched rearing started later for

fish from the Simojoki population (0+, paper I) than for fish from the Tornionjoki

population (from the yolk sac stage in paper II and from eyed egg stage in paper V). The

basic principles were similar; Offspring of wild-caught or hatchery reared parents were

reared in standard or enriched rearing environments, giving us four treatments: captive

standard (cs), captive enriched (ce), wild standard (ws) and wild enriched (we).

Environmental enrichment included physical structure in form of pebbles (from egg stage

until start feeding, Fig. 2a and Fig. 2b respectively), shelter for juveniles (bricks that were

placed beneath and on top of a black plywood plate, Fig. 2c) and shelter in outdoor

ponds at smolt stage (concrete blocks on top of PVC plates that rest on boulders, Fig. 2d)

and irregular changes in water level, current and velocity to mimic stochasticity of a

natural river environment. Enrichment was applied to fish reared in conventional rearing

tanks and at densities used for rearing fish for stocking purposes (Vehanen et al. 1993).

All fish from the Oulujoki population were reared with standard methods because here

we wanted to estimate the benefits of a soft release method on survival and migration of

stocked fish.

Study design

The study was two-folded, first we investigated the effect of broodstock origin and

environmental enrichment on traits important for restocking releases into the wild and

second, we compared the release methods that are currently used when stocking fish

with soft release methods.

The idea behind rearing fish of wild origin with enriched methods was to test for the

relative significance of genetic changes in a few generations in captive breeding. The

ultimate goal was to create fish with higher chances to adapt to a life in the wild after

release to increase survival. For example, for releases at the parr stage it is important to

adapt to the river habitat, including seeking shelter and to learn to forage on novel live

prey. While this is also important for salmon smolts in order to prevent predation and to

grow, smolts are additionally expected to start migrating to feeding grounds in the sea

and therefore migration (e.g. speed) is one of the behaviours that are crucial at this

stage. Monitoring fish after release into nature would give us an indication of their

survival, but would not show us how an eventual improvement is generated. If enriched

fish would eventually show higher survival, we wanted to know which mechanisms were

25

26

responsible for these improvements, whether it was improved foraging abilities or

antipredator avoidance. Observing and quantifying complex behaviour is virtually

impossible in the wild as fish are extremely difficult to monitor for obvious reasons and

because of uncontrollable factors like predators, competition and fluctuations in

environmental conditions. We therefore desired to test the fish in an environment that

largely resembled natural conditions, but at the same time was controllable for factors

that could easily have masked or spoiled our results if tested in the wild.

We therefore chose semi-natural outdoor streams (Fig. 3) to test for the effects of origin

and rearing on foraging capacity between cs, ce, ws and we parr in paper I and when

investigating the effect of rearing on foraging in the vicinity of a predator in paper II. This

system was simulating similar conditions as the fish would meet after a release into the

wild as the ponds were provided with water from the nearby lake and with natural

production of live prey in the gravel bottom (e.g. insects and insect pupa and larvae, as

observed by drift- and kick net sampling), but without the danger of losing the fish to

predation. To rule out the effect of competition, the parr were placed in individual cages

in paper I. Foraging capacity was measured from stomach contents of the parr. Fish were

left in the streams for different durations (8h, 12h, 24h and 38d). Hatchery fish have

previously shown to have the ability to learn foraging on natural prey. The study was

therefore designed to give us an indication of the time the fish would need to learn to

feed on the natural prey novel to them (stomachs containing natural prey). The parr

were additionally measured for specific growth rate in the trial of longest duration (38d).

For paper II ws and we parr were tested for their ability to make a trade-off in foraging

when exposed to a predator, either as parr that were allowed to swim freely in the

streams or in the same cages as parr from paper I. The stomach contents were analyzed

and Passive Integrative Transponder (PIT) technology was used to detect parr

movements with a predator present vs. predator absent (see PIT-tag system as in Fig. 4).

27

The second part of my thesis focused on the stocking method. Stocking is a stressful

procedure for the fish, with the potential to decrease cognition and other factors

important for survival (e.g. immune response, Bonga 1997). This may have negative

effects for the integration of the fish into the wild. Stocking includes handling, loading,

transport and release of fish into a novel environment. We therefore tested the effects of

these factors on the stress indicators plasma cortisol, blood glucose, plasma lactate and

time to navigate through a maze (Fig. 4). We also tested the recovery after stress, i.e.

how much time the fish needed before stress indicators returned to baseline levels. This

is important knowledge as it has been shown for many other species and also for fishes

that adequate recovery and acclimatization to the new environment after transfer (by so-

called soft release methods) can increase survival chances after release. We performed a

radio telemetry study to test whether soft release methods could be beneficial also for

our study model. Based on the results of the soft release study, we applied a soft release

method when conducting another telemetry study in 2012. Here we released smolts

from all four treatments cs, ce, ws and we into the Tornionjoki River to test differences in

survival between treatments after release.

The methods for manuscript I, II and the maze in manuscript IV had to be developed first.

No studies had been performed in these systems before and many pilot trials were

necessary to get them running. Intensive piloting was also necessary for manuscript V,

because this was the first telemetry study on Atlantic salmon smolts in the Tornionjoki.

Hence, the nature of the river was unpredictable.

Field and laboratory procedures

Stomach content analysis

Stomach content analyses were used for the parr in manuscript I and II. We used

stomach flushing for sampling of stomach contents (Robertson 1945). Water was

pumped into the stomach cavity through a metal needle, which was attached to a

mechanical handpump (1 bar) and stomach contents flushed out through the

oeseophagus. The contents were collected from the mesh net and conserved in 70 %-

ethanol (Vehanen et al. 2009). Stomach contents were weighed for total wet weight

28

(manuscript I and II) and total number of prey were counted (manuscript II) and

categorized into families or into species where possible. Stomach contents were weighed

for total wet weight and separately for larval and adult insect families in manuscript I.

Plant-material was included in manuscript I, but not in manuscript II (here the amount of

plant material in the stomach contents was negligible). Wet weight of the biomass

ingested was measured at 0.1 mg accuracy.

Blood sampling and stress indicators We compared the effects on stress levels with control fish by analyzing plasma cortisol

and blood glucose concentrations in manuscript III and IV and plasma lactate in

manuscript III. Plasma cortisol is an indicator of acute stress and was used for measuring

the direct effects of handling and transport. Blood glucose is an indicator of acute activity

and plasma lactate indicates past anaerobic muscular activity. With all three stress

indicators combined we could gain a total picture of the physiological changes that

occurred after handling and after transport as others have done before us (e.g. Iversen et

al. 1998; Arnekleiv et al. 2004; Hyvärinen et al. 2004).

The blood sampling procedure was the same in both experiments. We killed the fish

quickly with a blow to the head and took blood samples from the caudal vein with pre-

heparinized (Heparin lithium salt, 50 KU, ICN Biomedicals inc.) syringes fitted with 21-

gauge (0.8 x 40 mm) needles. We placed them instantly on ice in 1.5ml Eppendorf tubes.

Glucose concentrations were analyzed from fresh whole-blood immediately using

disposable cuvettes and a HemoCue Glucose 201+ instant reader. Then we separated

the plasma by centrifuging (Microcentrifuge Sigma 1-14) the blood in Eppendorf tubes

(4000 x g) for 10 minutes. We froze the plasma samples in Eppendorf tubes at -80°C until

later analyzed for cortisol concentration using commercial RIA-kits (Gamma-Coat Cortisol

CA1549E, DiaSorin, USA). We analyzed plasma lactate concentrations photometrically

from single (1:5 diluted) samples using lactate assay kits (Lactate Assay Kit II #K627-100,

BioVision Inc., USA).

PIT- telemetry

PIT-tag (Passive Integrative Transponder) technology was used in manuscript II and IV.

The tagging procedure was the same in both experiments; first, fish were anaesthetized

with MS-222 (100 mg/l). Then a 5mm incision was made on the ventral surface posterior

to the pelvic fin and the PIT-tag (23 x 4 mm, 0.6 g half duplex PIT-tags; Texas Instruments

Inc., www.ti.com) was inserted into the body cavity. A stationary two port antenna PIT-

system was continuously detecting smolt movements in the semi-natural streams (Fig.

3). In manuscript II, one antenna was installed around the start box and one at the end of

the race (Fig. 3). In manuscript IV the test area was divided into predator side (or control)

and release side. The two port antennas were installed in between the two sides, so that

parr movements could be detected in and out of the predator area for estimation of time

29

spent in each habitat and activity between the areas. For paper II we had eight antennas

running at the same time, two in each of the four ponds. For paper IV we had 32

antennas, 4 antennas in each pond. Each antenna was connected to a reader via a Texas

Instrument tuning module. The readers were connected to laptops, with a maximum of 8

antennas per laptop. ID, date and time were logged from each antenna nine times per

second as ASCII and the TIRIS data logger program (Citius solutions Oy, 2009) was used to

produce the ASCII data files. For paper II individual bypasses of each antenna and the

direction of bypasses was obtained by using chronological order of observations from

two antennas between release and predator area. The PIT-Data (N. Vuokko, 2007–2010)

software package was used to calculate the time spent in release or predator area.

Number of visits to the predator area was calculated by using AV Bio-Statistics 4.9

software (http://www.kotikone.fi/ansvain/avbs/). For paper IV swimming time between

start box and end of maze was calculated manually from the ascii data. We tested the

reliability of the recordings prior to the trials by simulating swimming movements

bypassing each antenna with a PIT-tag and were checking the laptop recordings

simultaneously. We rated the system as satisfactorily when the time of detection on the

laptop matched the time of the PIT-tag bypassing the antennas.

Radio telemetry

Radio telemetry was used for the studies described in paper IV and V. The tagging

procedure was similar for both years; before tagging fish were anaesthetized with MS-

222 (100 mg/l). A 15 mm incision was made on the ventral surface posterior to the pelvic

fins and the radio-tag was inserted into the body cavity by pushing the antenna through

the body wall with the help of an injection needle. The incision was closed with one

suture. The tagging procedure took on average two minutes per fish. For fish released

into the River Varisjoki in 2010 we used Lotek-tags (model NTC-3-2, 6 x 4 x 16 mm, air

weight 1.10 g, 55 d operational life (4 s burst rate), ratio of tag per body weight was on

average 2.36%). Fish that were released into the Tornionjoki in 2012 were tagged with

ATS F 1535-tags (6 x 14 x 4 mm, air weight 0.85 g, 59 d operational life, ratio of the tag

per body weight for the reared smolts was on average 1.2 % and for the wild smolts 3.2

%). The movements of radio-tagged fish were recorded with automatic listening stations

(ALS, 2010: SLS, Lotek, model SRX-DL3, 2012: ATS, R4500s) that were installed in the

respective River and in the River outlets.

In 2010 in the Varisjoki each transmitter had a unique frequency and a numeric code

combination using 5 frequencies with à 20 codes per frequency (10 hard and 10 soft

release fish per frequency). The ALS’s were installed 200 m upstream and downstream at

distances 150 m, 500 m and 2000 m from the release site. There were additional ALS’s

below all seven hydroelectric power stations in the Oulujoki River. All ALS’s received

radio signals through nine elements Yagi-antenna.

30

In 2012 the river stretch was considerably longer (Fig. 5). The first ALS was located 3.8 km

upstreams of the release site and ALS 2 – 4 were located 3.0, 97.0 and 290.1 km

downstream of the release site, respectively. Each transmitter had either a different

frequency (range 140.000 – 141.990MHz, with a minimum difference between two tags

of 10Hz) or pulse rate (24 or 40 ppm) and was randomly divided between the five

treatments.

The fish were additionally tracked manually in both experiments from shore and boat

using a Lotek receiver (Lotek, model SRX-400) in 2010 and an ATS receiver (R4500s) in

2012. Manual tracking was used to confirm detections at ALS and determine if fish were

dead or alive (paper IV). Receivers were connected to a five-element directional

handheld Yagi antenna. The coordinates were obtained by Global Positioning System.

The reliability of ALS tracking was tested in beforehand by checking the range of the

receivers. For this radio-tags were submerged into the river (depth ~1 -2m). If the

receiver could detect the signal over the whole width of the river we considered it

reliable. If one receiver was not sufficient to cover the area, one or more extra receivers

were added.

31

RESULTS AND DISCUSSION

Three lines of evidence demonstrated that enriching the rearing environment enhances

post-release performance of hatchery reared Atlantic salmon; enriched rearing promoted

foraging rates, learning to forage on novel live prey, decreased risk-taking behaviour

under predation risk of parr and improved migration speed and survival of smolts. We

also found indications for a potential improvement of survival skills when using offspring

of wild parents, but these results were less clear than the rearing effect. Less clear was

also the effect of the soft release method on survival and migration, though

acclimatization clearly decreased stress levels and promoted start migrations speed,

which we later found to increase survival probability. The results together suggest that in

our study species enriching the rearing environment had the highest potential to

improve pre-release performance and survival of stocked fish, as well as to increase the

welfare of fish kept in captivity in general. The fish in this study expressed high

environmental plasticity, demonstrating the importance of rearing environment on

development of fish phenotype.

Effects of enriched rearing Performance in semi-natural environments

Our results showed clearly that enriched rearing promoted foraging capacity and learning

to forage on natural life prey in Simojoki parr (paper I) after release into a semi-natural

environment. The results were confirmed for parr from the Tornionjoki population

(paper II) and for Atlantic cod (Gadus morhua L., Moberg et al. 2011). However, the

foraging capacity of the enriched fish has not been compared with wild conspecifics yet.

Foraging is one of the most important traits for survival and improved foraging skills

likely enhances survival after release, as was shown by Czerniawski et al. (2011) who

proved that exposing Atlantic salmon and sea trout parr to live prey increased survival

after release to the wild. Brown et al. (2003) found that the ability to learn to forage on

novel prey in Atlantic salmon was only improved for fish that had been reared in

structurally enriched tanks. This was later confirmed for social learning in Atlantic cod

(Strand et al. 2010). However, the training methods in Brown et al. (2003), Strand et al.

(2010) and Czerniawski et al. (2011) were applied in small scales in the laboratory and it

has only been shown once to be applicable to large-scale systems (Maynard et al. 1996).

However, in the wild fish meet not only the challenge of novel prey, but also the risk of

predation. Fish have to make a trade-off between foraging and avoiding being eaten

themselves. We therefore wanted to know if the enriched fish could adapt their foraging

rates to predation risk.

In paper II we found similarly that enriched rearing promoted foraging efficiency on novel

live prey in the absence of predators. However, when a predator was present enriched

fish decreased foraging rates to the level of the standard fish. The standard fish did not

make this trade-off between foraging and predator avoidance, which indicates that only

32

enriched fish were able to decrease maladaptive risk-taking behaviour under predation

risk. Our results confirm the findings of Lee & Berejikian (2008) who found a similar

trade-off in exploratory behaviour made by juvenile steelheads (Oncorhynchus mykiss)

and Roberts et al. (2011) who found that fish reared in enriched environments (for only a

few weeks) decreased risk-taking behaviour in terms of boldness to leave a shelter. In

Roberts et al. (2011) it was difficult to disentangle the effect of enrichment from that of

predator conditioning, but this study is importantly showing the significance of the

rearing environment on development of fish behaviour. There are many studies

demonstrating potential methods to improve fish survival after stocking (e.g. Brockmark

et al. 2007; Brockmark & Johnsson 2010; Roberts et al. 2011), but very few that have

proven that enriched rearing increases survival upon release into the wild (e.g. Maynard

et al. 1996).

Migration performance and survival in the wild

In paper V we found for the first time evidence that enriched rearing increases survival of

Atlantic salmon smolts after release to the wild with 100%. This is confirming Maynard et

al. (1996) who reports a 50 % increase in survival for Chinook salmon smolts reared in

structurally enriched rearing environments. However, Berejikian et al. (1999) and Fast et

al. (2008) found negative effects of enrichment on survival of Chinook salmon using

similar methods and Brockmark et al. (2007, 2010) found no effect of structural

enrichment on survival at all. All these studies differ, however, substantially in rearing

conditions, species and/or populations and life stage studied.

Very few studies have actually tested survival of enriched fish after release to the wild.

This is rather peculiar, as survival after release is one of the main achievements we are

aiming at when developing rearing methods. I can only explain this by the very difficult

nature of these studies. They are time consuming and often require considerable

financial and human resources. Survival of fish in the wild is extremely difficult to

monitor and the available technology is limited. Survival is estimated by e.g. re-catches of

smolt traps or electro-fishing, by telemetry or PIT-technology and can potentially give us

inexact mortality data or causes for mortality. They can, nevertheless, give us valuable

indications of survival after release and new technology is developing rapidly.

However, our results indicated effects of enriched rearing on all investigated traits. What

is it in the rearing environment that causes these differences in development?

What are the possible mechanisms creating the observed phenotypes?

We cannot disentangle the effect of shelter from changing water features in our rearing

method, neither is it possible to disentangle the effect of one habitat component from

other habitat components of the same and between studies. I will here anyway review

and compare various studies that have used enriched rearing to shed light over the

potential effects that each parameter has to a) pinpoint the importance of different

33

rearing procedures between hatcheries on fish development and survival (see Thériault

et al. 2010; Moore et al. 2012), b) inspire future research and c) because others might

have use for it when developing rearing methods in the future.

First, physical structure is frequently applied in enrichment studies. Fish in my thesis

learned to utilize shelter, as they were frequently observed beneath, or swimming

actively between structures (own obs., Fig. 1). Seeking shelter is an important

antipredator tactic. Utilizing shelter also gives fish an additional energy advantage over

standard fish (Millidine et al. 2006) as was also indicated by higher growth rates and

condition factor in fish from structurally enriched environments compared with standard

fish (Brockmark et al. 2007). Studies have also shown increased navigation skills in

Atlantic salmon that were kept in structurally enriched tanks (reviewed in Ebbesson &

Braithwaite 2012), which may have contributed greatly to migration speed and

concurrent or consequent in-river survival found in paper V.

In their study, Maynard et al. (1996) suggest that it was the influence of gravel substrate

that enhanced cryptic coloration of the salmon, which decreased susceptibility to

predators and consequently increased survival after release to the wild. But Berejikian et

al. (1999) used gravel substrate in their studies as well and they found, contrary, that

standard smolts had higher survival. Thus suggesting that the gravel alone was not the

responsible factor for higher survival in Maynard et al.’s studies or other factors in

Berejikian et al.’s rearing environment masked the effect of the structure. Another

example where studies use similar a method with different outcome is from Brockmark

et al. (2007) who utilized shredded green plastic bags with rocks in the bottom. These

were changed for every third day. In paper I we suggested that Brockmark et al.’s (2007)

shelter might not caught the characteristics of shelter in natural streams and could thus

explain that they found little effects of structure. However, in a recent study, Näslund et

al. (2013) used similar black shredded plastic bags and found effects in form of cortisol

decrease and improved shelter seeking of Atlantic salmon smolts. The difference in

Näslund et al.’s methods was that they did not remove the shelter. The difference could

also derive from that they were investigating different traits than Brockmark et al. (2007,

2010). Probably the cause is to be found in the feature of the shelter, as Lee & Berejikian

(2008) used rocks as structure and showed that structure promoted behaviour, but only

when the structure was stable. Additionally, Brockmark et al.’s studies indicated small

effects of structure also in combination with decreased densities. I found these

differences in Brockmark et al.’s results and methods compared to ours extremely

interesting (as most other studies show positive effects of enrichment). What puzzled me

here was that the shelter seemed appropriate when applied at low densities, but in the

high density treatment, however, it seemed that most of the fish (due to the large

number of fish) were not given the advantage of a shelter. There seemed to be relatively

more fish per shelter than in the low density treatment. This is not meant as a critique of

34

the methods applied by Brockmark et al. (2007). What I want to pinpoint here is that

small human influences can lead to changes in the animal’s environment that we are not

able to perceive or simply oversee, but could possibly lead to substantial changes in how

the animal perceives the environment and has the potential to hugely influence

development of a species that is highly plastic to its environment (e.g. Thériault et al.

2010).

High phenotypic plasticity in fish is very clearly indicated by Brockmark’s (2007, 2010)

studies, as they importantly show that changes in rearing density is crucial for the

development of fish phenotype. Larsson et al. (2012) found that decreasing lipid contents

before release promotes migration and survival of brown trout smolts and benefits of

lowered fat contents where confirmed for Atlantic salmon smolts (Vainikka et al. 2012).

In the study of Larsson et al. it was, however, difficult to determine if the effect was

really due to lipid contents or due to lowered densities in the rearing environment, but

also Vainikka et al. (2012) found in a study on Atlantic salmon a difference in migration

tendency between salmon on high and low lipid diets.

Changes in water features

While Berejikian et al. (1999) used a feeding system which introduced the food from the

mid-water column; Maynard et al. (1996) used underwater feeders which introduced

food from the bottom of the tank. This introduced a change in feeding conditions, as fish

were encouraged to feed from a bottom position. Also Fast et al. (2008) applied feeding

from the bottom, but a slightly different system and enriched Chinook smolts in that

experiment showed lower survival than standard fish. However, in Fast et al. (2008) there

was no gravel substrate as in Maynard et al.’s studies (and pebbles as in paper V), but

they had painted the raceways with camouflage colors. Unfortunately we know little

details about the rearing conditions in these studies.

Our rearing methods included additional irregular and unpredictable changes in water

current direction and velocity, which concurrently led to changes in many aspects of the

physical environment. Alterations of water features made habitat features and food

dispersal unpredictable. At times with high water levels the enriched salmon could catch

prey like under standard hatchery conditions by surface feeding and in the mid-water

column. In the semi-natural outdoor streams we found adult insects, mysis, and certain

pupa and larvae by drift-net sampling. However, when water levels were low they had to

adapt a more bottom feeding behaviour. Here where we found certain pupae and larvae

and Asellus aquaticus in the outdoor-streams by kick-net sampling. These were

important prey for fish, as indicated by the stomach contents of the study fish in paper I

and II. In periods of low water velocity fish could forage as standard fish, but when the

velocity increased, they were forced to react faster when catching the pellets. The fish

had to learn to adapt to changing conditions, which probably lead to increased cognitive

35

abilities through neural brain plasticity (Ebbesson & Braithwaite 2012). Thus it is likely

that the changes applied during rearing taught the fish to learn foraging under changing

conditions and were likely responsible for the enhanced foraging efficiency and their

ability to make a trade-off in the vicinity of a predator.

The changes in water velocities may also have improved swimming performance. Studies

on swimming training have similarly applied temporary high water velocities, alternated

with periods of low water velocities. This training regime has long known to increase

swimming performance (Farrell et al. 1990; Anttila et al. 2006). Swimming ability is

crucial for fish in order to maintain its foraging position, to escape predators and for

swimming long distances during e.g. migrations to feeding grounds in the open sea.

Our method could not disentangle the effect of structure from the effect of the changing

water features, which was not the aim of our studies either, but when comparing our

results with other studies it seems obvious that structure alone has the potential to

promote the development of certain behaviours and life skills, but is not sufficient to

create the whole repertoire of a wild fish. What seems to be of great importance for the

results are the differences in practices and rearing procedures between different

hatcheries, which have lately been shown to influence survival, relative reproductive

success and life history (Thériault et al. 2010; Moore et al. 2012).

Effects of broodstock origin

We found little evidence of origin effects throughout the studies. Our results support the

results of Chittenden et al. (2010) who found no effects of domestication on survival of

Coho salmon (Oncorhynchus kisutch). They found, similarly, a strong effect of rearing

environment using natural rearing. One explanation could be that any genetic effect on

life-history traits could have been masked by strong effects of the rearing environment as

fish express high phenotypic plasticity to their environments. But the genetic differences

between wild and hatchery parents in that study are, similar as in our studies, unknown.

Another likely explanation for the lack of genetic effects is probably that there was low

genetic variation between wild and hatchery fish.

Other studies have reported differences in behaviour and fitness declines already after 1-

2 generations in the hatchery (e.g. Salonen & Peuhkuri 2004; Araki et al. 2007; Christie et

al. 2012). In paper I we found genetic differences between fish of wild and hatchery

offspring and that offspring of wild origin started to forage on adult prey earlier (8h after

release) than offspring of hatchery parents. Also in paper V we found small indications

for broodstock effect on survival or migration behaviour, but we have no genetic data

from these fish. Effects of domestication have been also been found in salmon and

brown trout populations that had undergone directed selection, but these effects

36

weakened with time in captivity and were probably superseded by environmental

influences (Johnsson et al. 1996; Johnsson et al. 2001; Sundström et al. 2004).

The hatchery populations we used had been held in captivity for 2-4 generations and had

not gone through intentional genetic selection. It was therefore surprising that we found

differences between hatchery and wild origin at all. Anyway, the founder populations of

captive breeding programs of fish are small, these fish can therefore suffer from genetic

drift effects and loss of genetic variation can occur rapidly. This was also indicated by the

genetic data of the Simojoki population. The genetic data suggested for higher

homozygosity in the offspring of the hatchery fish than for the offspring of wild-caught

parents. Additionally we found a higher internal relatedness (IR) in offspring of hatchery

fish. This loss in gene diversity could have been caused by both genetic drift and

inbreeding and is likely responsible for the observed genetic differences in foraging

capacity. However, the genetic samples were not obtained from the study fish, but from

fish that had been reared in the same tanks. Therefore it is not clear if there were genetic

differences between the treatments in the experimental fish. However, a decrease in

genetic diversity as seen here can have potential implications for any stocking activities

using fish of hatchery origin, by reducing their viability in the wild. Genetic drift in

hatcheries cannot completely be avoided, but could be counteracted to a certain degree

by the acquisition of new brood fish. However, harmful inbreeding that potentially leads

to the deterioration of allele frequency can and should be avoided by proper breeding

management.

Additional causes that could have contributed to genetic diversification and observed

differences in phenotypes, is differential mortality between genotypes. It is unknown

which fish survived in the different environments we provided, as certain genotypes

likely adapted and survived better in the hatchery environment. Thus, even if large

numbers of broodstock fish are used to maintain high genetic diversity in breeding

programs, the differential mortality is difficult to detect and to manage.

Vainikka et al. (2010) suggest that Tornionjoki fish are the least domesticated of all

Finnish salmon populations and the offspring of hatchery fish we used were only 1st

generation paternal and 3rd – 4th generation maternal hatchery bred. However, we found

small tendencies that the enriched rearing might had a better effect on wild-origin fish.

Was this caused by genetic drift, which is working rapidly on creating genetic

differentiation between hatchery and wild populations? Or could differential mortality

also have played a role here? To answer these questions, it would be valuable to obtain

genetic data from the hatchery and wild offspring from this population. However, wild

smolts caught from nature were performing best in paper V. Others have found similarly,

that offspring of wild parents seem to perform better in the wild than offspring of

hatchery parents, but real wild fish do still perform best in nature (e.g. Araki et al. 2007;

37

Christie et al. 2012). We can therefore not exclude the possibility that the small effects of

origin we were able to detect here can have profound influences on other life-history

traits than tested here. These effects could also affect the fish during other life-stages

and affect the adaptability of the population as a whole, as domestication can affect

reproductive capabilities of salmon (Araki et al. 2007).

The benefits of the soft release

The lack of direct evidence on benefits of soft release methods on survival in paper IV

mirrors the available literature on this subject. Studies that aimed at examining effects of

acclimatization before release show contradictory results. I want to emphasize again on

the difficulties of conducting studies in nature, as many factors can mask the effects of a

soft release, like high predation densities. On the other hand, when looking at the results

from paper IV and V they indicate firstly, that acclimatization decreased stress levels and

promoted initial migration speed. We should not disregard that acclimatization had a

positive effect on survival of enriched fish in the telemetry study in River Tornionjoki.

Though, this was not the aim of that particular study and I can only speculate which

contribution the soft release had on our results in paper V. This study should be repeated

with a crossed design, testing enriched versus standard fish coupled with soft versus hard

release. The reason that we found no differences in survival between soft and hard

release fish in 2010 was most likely because the test distance was too short. We were

testing a river stretch of 3 km and in the Tornionjoki River differences in survival

appeared first at ALS 3 (97 km from the release site). The study in the Varisjoki shows,

however, the same trend as we also found in 2012 in the Tornionjoki; fish that expressed

faster start migration speed also had a higher probability to survive than slow fish.

Reflections

When reflecting over the results of my thesis and the results of other studies, the

similarity in behaviour of enriched and soft release fish is striking. Enriched fish started

foraging earlier than standard fish in paper I. Fish show that they are able to learn, but do

so better when reared in enriched environments (Brown et al. 2003; Strand et al. 2010).

It is know that stress impairs cognitive abilities (e.g. Wood et al. 2011). Salvanes &

Braithwaite (2005) found that Atlantic cod that experienced structure were recovering

faster from a stressor than standard cod. Releasing animals into a novel environment is

stressful, as was also indicated by our study in paper III; Stressed smolts were slower in

navigating through a maze than control fish. Wood et al. (2011) found the same in a

different species of fish. The smolts that survived until ALS 4 in paper V had faster start

migration speed than those that did not survive until ALS 4. In manuscript IV on the

benefits of a soft release we found that the hard release fish had higher stress levels

after release and were starting migration later than the soft release fish that had lower

stress levels. In an unpublished study Salvanes et al. found that Atlantic salmon reared in

enriched tanks found their way faster through a maze than standard reared fish

38

(reviewed in Ebbesson & Braithwaite 2012), as we found similarly in paper IV for fish that

had not been transported. Comparing stress levels of enriched and standard fish directly

after release would therefore be extremely interesting.

Taken together this is convincing me that much of the improvements that have been

found in enriched fish’s development are caused by an enhancement in stress tolerance;

their ability to handle stress and to recover faster from stressors. Näslund et al. (2013)

found that fish from plain hatchery tanks had two to three time higher plasma cortisol

levels than fish from enriched treatments. The levels were so high, that it indicates that

standard fish suffer from chronic stress. This can also explain the higher metabolism in

fish reared without structure (Millidine et al. 2006). Additional changes applied to water

features are probably also stressing the fish, but this is training them to cope with

sudden acute stress and not chronic stress as the absence of shelter, but rather sharpens

their adaptation abilities as they become habituated to sudden changes in the

environment. Jointly structure and changes could have an additive effect on the

development of stress tolerance in enriched fish leading to improved cognitive abilities

and likely higher survival chances after release to the wild.

CONCLUSIONS AND REMARKS

We found little evidence that genetic effects influenced behaviour and survival in this

study, but this was probably due to little genetic differences between wild and hatchery

offspring. The environmental effects were clearly stronger, showing that salmon express

high environmental plasticity. This study contributed to demonstrate how crucial the

rearing environment is for phenotypical development of salmonids and should not be

disregarded in stocking programs.

The enriched rearing methods used in the study are readily applicable to large rearing

systems and have the potential to enhance post-release survival and fish welfare. The

methods are simple, so that it would be easy for fish farmers everywhere to apply similar

methods with low costs. Since this project started the rearing methods have already

been taken into practice. A manual with instructions for enriched rearing is under

preparation by the FGFRI and they are also organizing courses for private fish farmers

and power company fish farmers on how to integrate the rearing methods into their

rearing systems. The government buys Atlantic salmon for stocking from private fish

farmers (sopimuskasvatus = contract rearing) and the FGFRI is responsible for transport

and for stocking of the contract-reared fish. FGFRI is making the rules for the quality of

fish (e.g. size, condition factor) and adopting enriched rearing methods for contract-

reared fish has been discussed among the researchers of the FGFRI. However, enriched

rearing has not always proven to promote survival in the wild (e.g. Berejikian et al. 1999

Brockmark et al. 2007; Fast et al. 2008). Moore et al. (2012) found great differences in

39

post-release survival between smolts that had been reared in two different hatcheries.

This is showing how variable results can be when rearing fish under different conditions

in different hatcheries. At the moment the FGFRI has an ongoing contract with four

different aquaculture facilities. These are rearing Atlantic salmon with similar rearing

methods as applied during the current study. Eggs from the same brood fish are under

rearing at two different stations and will be released into the same river to examine if the

hatchery effect can mask for the effect of enriched rearing. Whether or not these

methods will be integrated into fish rearing depends partly on the practical experience

from the other fish farms than the Paltamo facilities and also on more evidence of the

cost-efficiency of this method.

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