Age and Growth of Fish

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Age and Growth of Fish

1. Definitions and metrics
2. Three primary ways to estimate growth

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Age and Growth of Fish

• 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?

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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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How the metrics are related

• Length Frequency Analysis

W 3.3287L-12.689
W.000004L3.2603
W 2.8401L - 10.662
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3 ways to estimate growth in natural populations

• Length Frequency Analysis
• Recaptures of individually marked fish
• Back calculation from calcified structures

Caught
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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
You Come back a year later....
Population is 10000 fish
...at best maybe 60 survived....
You catch and tag 100 fish, good effort, but
...maybe only 10 lost their tags
.... so there are 54 tags in 10,000 fish
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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.dfg.ca.gov/.../FishTagDescriptions.htm
www.dfg.ca.gov/.../FishTagDescriptions.htm
www.daybreakfishing.com/TaggingFish.html
www.dfg.ca.gov/.../FishTagDescriptions.htm
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T-bar, dart, floy tags old school
www.fishinginpuertorico.com/page_ds10.htm
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Coded Wire Tags new school
http//www.hafro.is/catag/myndir/cwt.jpg
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PIT Tags newest school passive integrated
transponder
www.bnl.gov/.../Herpetological_Inventories.htm
www.absc.usgs.gov/.../coho_archivetags_obj2.htm
www.hpl.umces.edu/facilities/fishhatchery4.htm
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Tags for small fish Visible Implant Elastomer
new school
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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
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Age
Age this 358 mm largemouth bass is 10 years old

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Processed 76 largemouth bass Crampton Lake
(border upper penn. and WI)
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Back Calculate Growth
10

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3
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Back Calculation
Age this 358 mm largemouth bass is 10 years old
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AGE

2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
YEAR
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Other structures used for aging
Cleithra - Esocidae (sacrifice)
http//www.palaeos.com/Vertebrates/Bones/Dermal/Op
ercular.html
Opercula (sacrifice)
arvidsfishingreport.com/
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Other structures used for aging
Fin Rays anything where scales don't work and
you don't want to kill the fish
Vertebrae-Sharks (no spines, teeny otoliths)
www.fws.gov/midwest/alpena/rpt-stnib02.htm
www.pac.dfo-mpo.gc.ca/.../lingcod/ling_aging.htm
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How we look at growth data ...ie figures!
Size at age
How do we quantify how these populations are
different?
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Von Bertalanffy Growth Equation
Lt length at time 't'
L8 maximum length
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Problems with back calculation

• Lee's Phenomenon

LENGTH AT AGE
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
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Understanding Vulnerability and Sample Bias
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Which fish have been taken out already
Which fish are not represented?
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Fisheries Uses of Age and Growth

• What does the age structure look like

Walleye population in Lake Nevafishd
Maturity
Walleye population in Takemal Flowage
Maturity
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Fisheries Uses of Age and Growth

• What if the length limit on bluegill was 150mm

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Ecology of growth
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AGE

2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
YEAR
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What ecological factors might influence that
growth
Water temperature
Age
Climate or the Year
Food availability
Number of competitors
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