Reza Hakimimofrad-Assessments of Fish Populations I

7/31/2019 Reza Hakimimofrad-Assessments of Fish Populations I

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Assessments of fish populations I.

K. Limburg lecture notes, Fisheries Science

Assessments can take place at

any scale or level of

organization:

individual fish

cohorts

populations

communities & ecosystems

age

growth rate (changes in length or weight with age)

condition

abundance

fecundity, sex ratios

mortality (and sources thereof)

production of biomass

etc.

We can monitor the condition (state) of individuals,

cohorts, stocks, etc., via key indicators, such as:

One of the most important properties that we tend to

look at is the age of fish.

If we know ages, we can begin to understand all of the

complex age-dependent processes, some of which

weve started to discuss (e.g., age at reproduction)

Fortunately for fisheries biologists, most fish carry

with them the means for determining their ages, and

even growth rates and other life history events:

We can call these chronometric structures of fish.

The paramount importance of AGE.Age estimation in fishes

Chronometric structures include:

Scales

Otoliths

Opercular bones

Cleithra bones

Vertebral bones

In many (but not all) cases, one or more of these will help us

learn how old a fish is


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Cycloid (left) and ctenoid (right) scales

Haddock European sea bass

Operculi from haddock vertebra

Otoliths

(literally, ear-stones)

There are 3 pairs

of otoliths

sagitta (arrow)

lapillus (little

stone)

asteriscus (little

star)


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Photo presented by Dr. Arthur Popper, U. of Maryland, at 2009 International Otolith Symposium

Sagitta

Lapillus

Asteriscus

Otoliths come in many sizes and shapes

built-in chronometers in fish heads

20 mm American shad larva

Annual rings

Salmon


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Otolith of a very long-lived

deep-sea fish (Sebastes sp.)

Transverse section

showing annuli

Daily increments (sagittal section)

Source: Maryland DNR

Otolith marking


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Thermal

marking

method

Alaska Dept of Fish and Game

Douglas Island Pink & Chum, Inc

Pros and Cons of Scales vs Otoliths

Scales:

Dont have to kill a fish

Adequate for young orshort-lived fish

Resorption or remodelingpossible

Can fall off & regenerateCan stop growing failsto track age

Otoliths:

Accurate info to daily level

Better for long-lived fish

Physiologically inert

Chemical analyses

Killing is necessary

Sometimes, decouplingfrom somatic growthoccurs

Validation always a must!!

Otolith microconstituents increasinglyused as natural tags

Sr is particularly useful to trackdiadromy

Sr, like Ca, is an alkaline earth element with

similar ionic radius can substitute for Ca in

the otoliths aragonite

[Srmarine]generally >> [Srfreshwater]

Can use Sr:Ca ratios to trace salinity histories

of fish

Measuring Sr in otoliths

Microanalytic techniques

Wavelength dispersive

electron microprobe

(WDS), can make

point transects on the

order of microns

Otolith # 1809

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 200 400 600 800 1000 1200

Distance from Core (mi crons)

Sr:Ca

x

1000


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Nuclear microprobe combined with proton-

induced x-ray emission analysis (PIXE)

- higher resolution technique

- able to measure multipleelements at ppm levels

- can map entire otoliths

quickly

Conducted for specific applied problems

with Baltic Sea fish

In the meantime, I learned just how complex

the modes of diadromy can be!

Case studies:

Revealing Complex Life Histories of Fishes ThroughNatural Information Storage Devices: Case Studies of

Diadromous Events as Recorded by Otoliths

Sweden

Switzerland

Baltic Sea

European brown trout, Salmo trutta

Thought to be either freshwater or

anadromous, requiring at least a year in

fresh water (smolt transformation)

We studied migratory behavior in fish

from Gotland in the Baltic Sea, where

populations are somewhat threatened


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GotlandSpawners exceed smolt

production in many Gotland

streams many small, ephemeral

Q: where do they come from?

Mostly not highly migratory

Fry (pre-smolt) can spill out of

small streams, or be chased out Q: Can they survive/recruit in sea

without a smolt stage?

Collected spawners in Ar Brook (0.25 km)

Hultung Br. (3.5 km) Bngn Br. (4.0 km)

Also collected adults at sea

Removed & assayed otoliths

Ingmar Bergman lived here

Validation

study:

Sr:Ca ratios

Sea-run Mom

Very flexible modes of anadromy!

New to Science


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Brown trout findings:

Relatively few precocious emigrants in either

the spawning stock or recruited adults at sea

On the other hand, many other modes of

anadromy and habitat use, including completely

marine (i.e. brackish) lifestyles this is why

spawners exceed smolts on Gotland (flexibilitysimilar to some Pacific salmonids)

Implications for management & climate change

To conclude:1. Detailed demographic studies of fish populations

are possible

2. These can, and are, intimately tied to our assessment

models

3. A number of bio-chronometers are useful

4. In particular, otoliths can provide a wealth of

demographic and environmental information

Photo: Mary Ziemba

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Reza Hakimimofrad-Assessments of Fish Populations I