age, size and growth zoo 511 week 3 slides. metrics of size and growth length –pros: easy,...
TRANSCRIPT
Metrics of Size and Growth
• Length– PROS: easy, intuitive, history in angling, length
rarely shrinks, nonlethal – CONS: lots of change in biomass not related to
length
• Wet Weight (i.e., weighing a live fish)– PROS: nonlethal, quick, useful for large calculations
(ie population biomass)– CONS: can be difficult in the field if conditions are
bad
• Dry Weight (i.e., weighing a dehydrated fish)– PROS: accurate description of individual's mass– CONS: time intensive and lethal to fish
3 ways to estimate growth in natural populations• Recaptures of marked individuals
• Length-Frequency Analysis
• Back calculation from calcified structures
#C
augh
t
0
10
20
30
10 40 70 100 130 160 190 220 250 280
Recaptures of marked individuals
METHOD: measure individuals and give them unique marks; recapture and measure again later
PROS: nonlethal, accurate individual data
CONS: high effort - have to catch & mark A LOT of fish
Length-Frequency AnalysisMETHOD: measure population at least once; plot
length vs. frequency to find age classes; compare across age classes to estimate growth
0
10
20
30
10 40 70 100 130 160 190 220 250 280
#C
augh
t
Length (mm)
Age class 3
Age class 4
Age class 5
Age class 2Age
class 1
Length-Frequency AnalysisMETHOD: measure population at least once; plot
length vs. frequency to find age classes; compare across age classes to estimate growth
PROS: nonlethal; can use historic data; can do with 1 sample
CONS: “snap shot” of growth; assumes constant conditions; easy to bias sample with gear, time or location; requires lots of fish
0
10
20
30
10 40 70 100 130 160 190 220 250 280
#C
augh
t
Length (mm)
Back CalculationMETHOD: Examine hard structures from individuals
for age and evidence of past growth rate
Periods of rapid and slow growth show up as rings
Back CalculationMETHOD: Examine hard structures from individuals
for evidence of past growth rate
PROS: sometimes nonlethal; accurate individual data; no repeated sampling; does not assume constant conditions; can used archived structures; can estimate over small size/time changes;
CONS: sometimes lethal; can be technically challenging
Vertebrae (sharks)
Fin RaysOpercula
Cleithra (pikes & relatives)
Hard structures to estimate age & growth
Otoliths work the same way
Plus they are useful for many other things
But you have to kill the fish to retrieve them
And they are more work to process
Otoliths and fishery science
• Unique properties:– Otolith growth is continual– Lack of resorption
• Complete growth and environmental record– Crystalline structure
• Holds trace metals
• Scientists use otolith composition to:– Estimate what temperatures the fish
experienced in the past– Determine where the fish traveled (e.g.,
ocean vs. freshwater)
Frasier-Lee Equation
Lt= c + (LT – c)(St/ST)
big T means now
little t means some time in
the past
L means fish length
S means scale radius
Frasier-Lee Equation
Lt= c + (LT – c)(St/ST)
c is “Carlander’s constant” -- it will have a different value for
different species
Now we have a lot of length-at-age points.
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100
200
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400
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Age
Leng
th (
mm
)
How do we summarize growth patterns from this?
How do we compare growth between 2 populations?
Insert real data here?
0
50
100
150
200
250
300
350
400
450
0 5 10 15 20
Age
Fis
h L
en
gth
AL
WS
Von Bertalanffy Growth Model
Lt = L∞ - (L∞ - L0) –kt
– Lt = length at time “t” (of an avg. fish in the population)
– L∞ = length at infinity
– L0 = length at time zero (birth)– K = constant (shape of growth line)
Von Bertalanffy Growth Model
Lt = L∞ - (L∞ - L0) –kt
If you give the model
this
It will give you these