BI 2060 V071 Kaiser part three; Impacts Case study Trondheimsfjord The Trondheimsfjord is a relatively selfsustaining ecosystem. Of course, it is not hydrpgraphically

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Kaiser part three; Impacts Case study Trondheimsfjord

The Trondheimsfjord is a relatively selfsustaining ecosystem. Of course, it is not hydrpgraphically or biologically isolated from coastal waters, but it is so big and diverse with respect to biotopes and habitats that many species can complete full life-cycluses in the fjord. This applies to both evertebrates, fishes, seabirds and mammals.

Thus, one can use practical examples from the ecosystem Trondheimsfjord to examplify effects of human activity, viz:

• Fisheries• Aquaculture• Habitat disturbances and pollution • and• Conservation activity

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The Trondheimsfjord is the third longest and sevetnth deepest fjord. The distance from Agdenes (the outlet) to Steinkjær is 140 km, and the largest depth is 614 m. The fjord is divided into three main basins by thresholds at Agdenes, Tautra and Skarnsundet.

ABOUT THE TRONDHEIMSFJORD

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The Trondheimsfjord is very rich on fish species. More than a hundred fish species are present, including many of the most important Norwegian commercial fish (cod, saithe, haddock, whiting, blue whiting, hake, herring, sprat, and several flatfishes).The most important fisheries have been on cod, saithe and herring. In later years the commercial catch of herring has been closed due to the danger of recruitment failure. The traditional home fishery on cod and herring has long traditions in the human population and is quite free. Also, leisure fisheries is a widespread activity for a large part of the population along the fjord. The output from the cod fishery has been an On/Off situation in the last 50 years, tuned to variation in the stock size.The stock size variation show signs of being correlated with both milieu factors and exploitation pressure, as argumented for in the following treatment of the cod- and herring fishery in the fjord.

EFFECTS OF FISHERIES

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Trondhjem Biological Station (TBS) has performed fisheries biological studies in the Trondheimsfjord for more than a hundred years. Many research vessels has been serving during these years.

Sunrise mood onboard RV "Harry Borthen I". The Skarnsund bridge at the inlet to the Beitstadfjord

is a wellknown landmark.


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Gadoids (cod family) which

spawn in the TrondheimsfjordCod

Haddock

Whiting

Saithe

Pollack

Norway pout

Poor cod

Hake

Blue whiting


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Relative yearclass strengths of cod in the Trondheimsfjord 1963-1990 (Ekli 1997)

(cf next slide for extended period)


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Like many other fish stocks, the cod benefitted greatly from the catch stop during the second world war. After the war, the catches were good up to the 1960ies, and so also in the Trondheimsfjord. Then the output gradually decreased, making it more or less economically unprofitable to fish commercially in the fjord. This gave the stock a chance to recover for some years. From the middle of the 1970ies the fishery was good based on several strong yearclasses. This again lead to higher exploitation,e.g. by the participation of 20-30 large vessels from the coastal areas which used chains of up to 80 modern monofilament nets on the spawning grounds in Verrasundet(inner parts of the fjord). Apparently, this intense fishery was too much for the stock. The catches were graduallyreduced, and from the mid 80ies the fishery again became unprofitable for the boatsfrom the coast. The stock was left in relative peace, but the recruitment and yearclass strength were low in a substantial perion after that. Only in the mid 90ies strong yearclasses started to appear again. The causal relations are complex in marine ecosystems, but this story of the Trondheimsfjord cod seems to fit into some wellknown patterns (/. cont.)

THE VERRAN COD (VERRATORSKEN)


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/. cont.The size of a fish stock is a balance between annual recruitment and mortality.The natural annual mortality of cod in the Trondheimsfjord is ca 40% (Denstadli1970, Mork 1976). On top of this comes the fishery mortality. In overexploitedstocks the total annual mortality (natural plus fishery-related) is often 70% ormore. The cod is a multiple spawner, and a spawning stock in good conditionconsists of many yearclasses, included some big, old females for which a superior egg quality and egg survival than younger females. In particular, firsttime spawning females has a comparatively low survival of their eggs.In a heavily exploited stock the spawners will consist of a large portion of young females which, due to low quality eggs, will result in weaker yearclasses.If high mortality (intense fishery), a low mean age in the spawning stock (lowegg survival), and non-optimal natural milieu conditions (temperature, mismatch relative to the plankton bloom, predation on eggs) coinsides, a stock can collapse and stay at a low size for many generations. There are reasons to assume that this is part of the explanation for the history of the Trondheimsfjord cod since thesecond world war. Apparently, periods with a lower exploitation have given the stock a possibility to recover to natural size.

The moral is...?


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THE BEITSTADFJORD HERRING (BEITSTADFJORDSILDA)

It has been known for more than a hundred years that there is a local selfsustained and selfrecruiting herring stock in the inner part ofthe Trondheimsfjord (Beitstadfjord).That this stock is genetically isolatedfrom the coastal herring and Norwegian Springspawning herringwas confirmed by population genetics methods at TBS in the1990ies (Skjong 1994).

As common for herring stocks, the Beitstadfjord herring has showed somechanges in spawning place and over-wintering area in Beitstadfjord, butit has still remained local.


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BEITSTADFJORDSILDA /. cont.

Apparently, the Beitstadfjord herring struggles somewhat with maintaining a proper size of the stock. It isknown to be relative small by size (slow-growing) and meager compared to e.g. coastal herring. It is mainlya spring spawner. The spawning appears to have become more spread-out both geographically and temporallysince the 1980ies, but it still takes place in the inner fjord. The local exploitation has traditionally been performed by ground-owners and fishermen/farmers who have used a fewherring nets, and also by the use of light and beach seines. Place for use of beach seines was a right of the land-ownersand was listed in official documents for the Beitstadfjord.

Herring in the Trondheimsfjord was opened for catch for up to 10.000 tons per year in the 1950ies, but considerably lower (2.500 tons) from 1980 to 1985 lavere (2.500 tonn), at which time it was stopped due to bad recruitment to thestock. Since 1996 there has been a full closing of the commercial fishery.. Today, it is only allowed to fish for personalconsumption using one herring net. The traditional herring fishery in the Trondheimsfjord was not necessarily concerning only local herring. At the time of the year when the fishery took place, there can easily be a contribution from other stocks, e.g. coastal herring andNorwegian sprin-spawning herring in the mid part of the Trondheimsfjord.

The moral in this case is that the local herring stock in the Trondheimsfjord does not have suficient natural self-recruitment to with stand any substantial exploitation with modern, effective catch gear.For this reason, it must be subject to a more restrictive management and regulation than more productive stocks in Norwegian coastal- and oceanic waters.


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The angler fish (Lophius piscatorius) is found along the Norwegian coast up to Vesterålen. It gained its latin name from the "fishing rod" on its head, with which it lures its prey. The species was almost unattended in Norway until for 10-15 years ago. At that time it became a popular restaurant food and gave a good income for the fishermen. Old and very large individuals were caught in the beginning. Specimens of more than 40 kg was relatively common, and a record weight of over 70 kg is reported from the Trondheimsfjord. From being an almost unexploited stock with a large portion of old, large individuals, the catches are now reduced to one third, and the large individuals have become more rare. This species needs a long time for the rebuilding of the local stocks.

THE ANGLER FISH


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According to evolutionary theory, intensively exploited fish populations are expected to undergo genetic shiftstoward maturation at smaller sizes and/or younger ages, given that early maturing individuals will be more likely to reproduce prior to capture. Fisheries-induced evolution could thus lead to a loss of genetic diversity in life history traits. The Theme Section, organized by C. T. Marshall & H. I. Browman, discusses probabilistic maturation reaction norms in the context of disentangling evolutionary vs. environmental (genetic vs. physiological) influences on fish maturation (see figure to the right).

GENETIC EFFECTS OF FISHINGWITH SELECTIVE GEAR


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Kaiser part three; Impacts Case study Trondheimsfjord EFFECTS OF AQUACULTURE

FARMING IN NET PENS.RELEVANT SPECIES:Salmon – cod – blue mussel

SALMON: The Trondheimsfjord is one of the most important areas for salmon ascending to their rivers. Several large salmon rivers drain to the fjord (Orkla, Gaula, Nidelva, Stjørdalselva, Verdalselva, Steinkjærselva, Figga). From 1989 the entire fjord was regulated as temporary (5 years) security zone for salmonids; i.e. no new licenses for salmon and trout farming will be given within the zone. Later, the fjord has been suggested for the status of National salmon fjord. This will mean very strict bans on all farming activity which bear the risk of escapees, disease or other danger for the natural populations.

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Kaiser part three; Impacts Case study Trondheimsfjord EFFECTS OF AQUACULTURE

COD: Feeding of wild-caught cod to market size has been going on for some time in the Trondheimsfjord, but this is not regarded as an activity which represents a danger for the natural cod population. Some production of codlings for farmingalso takes place, but is land-based and not regarded as notregarded as a danger to nature.Recently, a company has applied for concession to establish a plant for farming cod in the inner part of the fjord. This is the first application of its kind in the fjord, and triggered a legally based process where The Ministry of Fisheries has sent the application out to a number of hearing instances, both official and non-official. The Ministry will make its decision based on the regulations of consessions and the the results of the hearings when these are available.

Among the conditions that probably will be treated by the hearing instances are:From where will the codlings for farming be collected (local stock or central distributeur in Troms??)Technical standard – security against wreckage and escapeEscape issues and potential effects on the local stockEscape issues related to the predation on salmon in the fjordDisease and infection issues – related to wild cod and other species Pollution effects on local bottom habitatsNorwegian legislation, consession rules, international obligations

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Kaiser part three; Impacts Case study Trondheimsfjord EFFECTS OF QUACULTURE

BLUE MUSSEL: Blue mussel farming has existed for many decades in the Trondheimsfjord,with variable success. Particularly in the early phases the trials were characterized by lack of knowledge and planning, and many producers went bancrupt because of algal blooms, wreckage,predation losses by seabirds, and an in general bad caretaking of the plants. In later years, more serious producers have establishe plants several places in the fjord, some with good results. The production is based on natural pelagic larvae which settles on ropes hanging in the watercolumn, and the larvae are not supported with feed of any kind. This industry is sensible for algalblooms. However, because a veterinary control is taken care of by the authorities, the risk has been reduced for dramatic production losses by harvesting in the wrong periods.Potential harm to natural habitats lies in detoriation of the bottom substrat below the plants. Concetrated faeces and dead mussels easily leads to local pollution of the bottom habitat. In lateryears more consideration has been given to favourable current conditions and removal of debris from theplants during the planning and localization process. The authorities has placed considerable work in coastal zone planning and localization criteria for blue mussel plants as well as other forms of farming and ranching.

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Kaiser part three; Impacts Case study Trondheimsfjord EFFECTS OF DSTURBANCES,

POLLUTION ETC

POLLUTION: The Trondheimsfjord has traditionally been debited with considerable pollution because it has had both a substantial industry (mining, erts shipping, quarries etc) and a substantial agriculture activity with run-off to rivers and ultimately to the fjord.

While mercury pollution from agriculture earlier was serious problem, regulations implementedby the authorities brought this problem under control.Also, legislation against fertilization in winter has reduced the run-off of nutrients (nitrates,phosphates) to rivers and the fjord. The earlier eutrophication effects with oxygen depletionin the bottom waters of local basins has to a large degree been solved.

In former industy societies such as Orkanger the pollutioning industry are terminated, and inlocalities such as the Orkdalsfjord a large part of the toxic compounds are now covered bynatural sediments.

In Trondheim, industry that earlier used the Nidelva and the fjord as resipients has been imposed strict rules for doscharge, and big cleansing plants for domestic waste has beenbuilt.

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Kaiser part three; Impacts Case study Trondheimsfjord EFFECTS OF DISTURBANCES,

POLLUTION ETC

The Trondheimsfjord acts as resipient for poisons, plant nutrients, waste and seawagw from a large geographical area and a substantial popuulation.

Several large studies on the pollution status of the Trondheimsfjord have been done. These have identified local problems, mostly quite near to the largest population centers and shipping harbours. However, the general picture is that the situation in the fjord is good, especially in comparison with fjords with industry in south and east Norway.

This is explained by the fact that the Trondheimsfjord is a very good recipient due to its large volume which has a good water exchange with the coast. The normal picture is that the fjord water is completely renewed by twice a year, one in the spring (April – Atlantic water) and one in the autumn (coastal water). In addition, the Trondheimsfjor has a substantial tidal water amplitude of 180 cm. Together with a typical estuarine run-off due to the large rivers this results in a stable ingoing net current on the south and east side, and an outgoing rest current on the north and south side of the fjord.

Together these physical factors gives good water renewal for the fjord, and makes it a very effective and robust resipient.

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POLLUTION ETC

In the last 10-15 years the sea water on the Norwegian coast has undergone anunusually strong temperature increase, some places on the coast as much as 2-3 degrees Celcius. This situation is also valid for the Trondheimsfjord. The monthly hydrographic measurements by Trondhjem Biological Station show that the temperature in the bottom water have increased unusually much since the 1990ies, and has set frequent "all time highs", latest in February 2007.

If this continues without the "correction" that was common in earlier periods, it will probably result in changes in the fjord's ecosystem. One of the probable scenarios is that the fjord looses its position as the "north boundary" for many marine species, and that the biodiversity of the fjord becomes poorer and more like thatin the fjords in southwest Norway today.

An ecosystem in change often gives opportunistic species a chance to establish themselves in free or new niches. Such species can easily take over the hegemonyas top predators, at least for a period.

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POLLUTION ETC

The Figure on the next slide shows a plot of the development in bottom temperaturein the three main basins in the Trondheimsfjord. The upgoing trend in clearly seen,and the latest measurements are "all time high" with a good margin since these measurements started early in the 1960ies.

In the latest 10-15 years or so, reports have been more frequent on the occurrence of fish with a more southern distriburence which have been found in the Trondheimsfjord (sworfish, tuna, horse mackerell, sea bass, goatfish, blackfish). At the same time, a specific jellyfish, the Periphylla periphylla, has established a large, selfrecruiting and seemingly stable population in the innermost basin of the fjord.It is still an open question if all these observations in any way are coupled to the ongoing temperature increase.

If an extensive change in the fjord's ecosysten is going on, it is even more importantto monitor the physical and biological proceses in the fjord in order to learn and gainexperience in the effects that are triggered by climatic changes. Some of these effectscan be quite grim even at out latitudes.

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POLLUTION ETC

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POLLUTION ETC

Periphylla periphylla (kronemanet) i Trondheimsfjorden

The coronate jellyfish(Periphylla periphylla) is anexample of an opportunistwhich can strike in eco-systems out of balance.

It has some basic propertieswhich makes it a powerfulcompetitor for the hegemonyas top predator.

Not surprising, really; its basiccharacteristics have survivedsome 550 million years ofevolution.

Documents

BI 2060 V071 Kaiser part three; Impacts Case study Trondheimsfjord The Trondheimsfjord is a relatively selfsustaining ecosystem. Of course, it is not hydrpgraphically