Age and Growth of Fish

1. Definitions and metrics

2. Three primary ways to estimate growth

Age and Growth of Fish

1. Age refers to years

• Aging fish, all fish have a birthday on January 1

- Change with spawning time (spring or fall in WI)

• Age class is the year the fish is born

• Not that all that interesting in itself, used to describe growth

- Exceptions might be maturity

2. Growth is the change in length, wet weight, or dry weight over time

• Why so many metrics?

Different metrics of fish growth

Length

-Pros: easy, intuitive, history in angling, length rarely shrinks

-Cons: lots of change in biomass not related in length

Wet Weight

-Pros: used in large calculations (ie population biomass), metric used in production

-Cons: can take more time in field (rocking boat or wind and balance don't mix)

Dry Weight – fat weighs less then water but is way more valuable to individual. 24-72 hours at 60 degrees C (140° F)

-Pros: accurate description of individual's current state

-Cons: time intensive and must kill fish

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LOG (LENGTH)

LOG

(W

EIG

HT

)

How the metrics are related

• Length Frequency Analysis

W=.000004*L3.2603

W= 3.3287*L-12.689

W= 2.8401*L - 10.6620

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Length

Wei

ght

3 ways to estimate growth in natural populations• Length Frequency Analysis

•Recaptures of individually marked fish

Back calculation from calcified structures

#C

augh

t

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Length Frequency Analysis

Pros: non-destructive, archived lengths

Cons: have to catch lots of fish, unknowns are high!, easy to bias sample with gear, time, or location

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Recaptures of marked individuals

Pros: non-destructive, good individual data

Cons: have to catch TONS of fish to see a recapture

Population is 10000 fish

You catch and tag 100 fish, good effort, but

You Come back a year later.......at best maybe 60 survived....

.... so there are 54 tags in 10,000 fish

...maybe only 10% lost their tags

Estimating growth from tagging

Pros: understand the variability in individual growth

Cons: tag loss, tagging may influence growth, behavior, or mortality, cant read tag

www.daybreakfishing.com/TaggingFish.html

www.dfg.ca.gov/.../FishTagDescriptions.htm

www.dfg.ca.gov/.../FishTagDescriptions.htm

www.dfg.ca.gov/.../FishTagDescriptions.htm

T-bar, dart, floy tags –old school

www.fishinginpuertorico.com/page_ds10.htm

Coded Wire Tags – new school

http://www.hafro.is/catag/myndir/cwt.jpg

www.hpl.umces.edu/facilities/fishhatchery4.htm

www.bnl.gov/.../Herpetological_Inventories.htm

www.absc.usgs.gov/.../coho_archivetags_obj2.htm

PIT Tags – newest schoolpassive integrated transponder

Tags for small fish

Visible Implant Elastomer

– new school

Interpreting age from structures

• WE INTERPRET• we don't age, we don't assign ages

- seems overdone, but it is important, because it teaches you that you may be wrong, which is ok, as long as you know you might be wrong!

Cause Brian learned "the art" from Dr. John Casselman (OMNR)

2 main uses: Age and Back Calculate

Age

12

345678

9

Age = this 358 mm largemouth bass is 10 years old

10

Processed 76 largemouth bass

Crampton Lake (border upper penn. and WI)

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Age

Leng

th (

mm

)

Back Calculate Growth

7

3

10

y = 477.61x - 45.171

R2 = 0.847

y = 180.9x + 179.28

R2 = 0.7277

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Otolith Radius

Fis

h Le

ngth

Back Calculation Age = this 358 mm largemouth bass is 10 years old

20052004200320022001200019991998199719961995YEAR

109876543210AGE

0.950.920.880.830.720.670.590.510.40.290.09RADIUS

355345338330310300284197143890LENGTH

0107820101687545489GROWTH (mm)

Other structures used for aging

Cleithra - Esocidae (sacrifice)

arvidsfishingreport.com/

http://www.palaeos.com/Vertebrates/Bones/Dermal/Opercular.html

Opercula (sacrifice)

www.fws.gov/midwest/alpena/rpt-stnib02.htm

Other structures used for aging

Vertebrae-Sharks (no spines, teeny otoliths)

www.pac.dfo-mpo.gc.ca/.../lingcod/ling_aging.htm

Fin Rays – anything where scales don't work and you don't want to kill the fish

How we look at growth data ...ie figures!

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LMB Age

Me

an

Le

ng

thSize at age

How do we quantify how these populations are different?

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LMB Age

Me

an

Le

ng

thVon Bertalanffy Growth Equation

Lt L∞*(1 – e(-K*t))=Lt = length at time

't'L∞ = maximum length

Problems with back calculation

• Lee's Phenomenon

Age Yr.Class 1 2 3 4 5 6

1 1988 90

2 1989 85 113

3 1990 78 112 139

4 1991 75 108 133 150

5 1992 66 96 129 147 160

6 1993 59 92 126 147 156 166

LENGTH AT AGE

Understanding Vulnerability and Sample Bias

Which fish have been taken out already

Which fish are not represented?

Fisheries Uses of Age and Growth

• What does the age structure look like

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Age

% o

f th

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pula

tion

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% o

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Maturity

Maturity

Walleye population in Lake Nevafishd

Walleye population in Takemal Flowage

Fisheries Uses of Age and Growth

• What if the length limit on bluegill was 150mm

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Toledo Bend

Toledo Reservoir

Ecology of growth

20052004200320022001200019991998199719961995YEAR

109876543210AGE

0.950.920.880.830.720.670.590.510.40.290.09RADIUS

355345338330310300284197143890LENGTH

0107820101687545489GROWTH (mm)

What ecological factors might influence that growth

Water temperature

Age

Climate or the Year

Food availability

Number of competitors