Fisheries Abundance Estimates and Depletion Methods
Common Abundance Estimates
•
CPE/CPUE (relative density)
•
Depletion/Removal (estimate of N
0
)
•
Mark-Recapture (estimate of N
0
)
Abundance
1
Concept – Depletion Estimate
•
Consider this situation …
–
Sampling a pond with three fyke nets
–
No limit on number of sampling events (days)
–
Fish are removed from pond when captured
–
Compute CPE as … total fish/day
–
Compute cumulative catch prior to each day
–
What would the following graph look like?
Abundance
2
Concept – Depletion Estimate
Abundance
3
Development – Depletion Estimate
•
Define (along with N
0
, N
t
, C
t
, and q)
–
K
t-1
= cumulative catch prior to time t
•
i.e.,
•
Key relationship
•
Substitute CPE equation for N
t
and simplify
–
What type of function is this?
Abundance
4
Development – Depletion Estimate
Abundance
5
•
Use regression to
fit linear model
q = -slope
N
0
= intercept/q
Proportion Caught
•
As noted in CPUE module, q is proportion
of population caught with one unit of effort
but only if effort is small (and then it is only
an approximation).
•
q is an instantaneous rate that must be
converted to an actual rate with 1-e
-q
–
If q=0.02
then 1-e
-0.02
= 0.0198
–
If q=1.00 then 1-e
-1.00
= 0.0632
Abundance
6
Class Exercise
•
Do First Question
Abundance
7
Leslie Model Assumptions
Abundance
8
•
The population is closed.
•
Catchability (q) is constant.
•
All fish are equally vulnerable to capture method.
•
CPE is substantially reduced by fish removal.
•
Catches remove more than 2% of population.
•
Units of effort are independent - i.e., the individual
units of capture method do not compete with each
other.
K-pass Removal
•
Common in stream work
•
Several “passes” through an area are made
–
Number of fish captured are counted
–
Captured fish are physically removed
•
Derivation of estimates is complex.
–
Zippin and Carle-Strub methods are common
•
Carle-Strub somewhat more general
Abundance
9
Class Exercise
•
Do Second Question
Abundance
10
Explore common abundance estimation techniques like CPUE, mark-recapture, and depletion methods. Understand how to calculate relative density, depletion estimates, and cumulative catch. Discover the concepts of N0, Nt, Ct, and q in depletion estimates using regression models. Learn about the assumptions of the Leslie Model and the complexity of K-pass Removal methods in fish population assessment.
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Presentation Transcript
Common Abundance Estimates CPE/CPUE (relative density) Depletion/Removal (estimate of N0) Mark-Recapture (estimate of N0) 1 Abundance
Concept Depletion Estimate Consider this situation Sampling a pond with three fyke nets No limit on number of sampling events (days) Fish are removed from pond when captured Compute CPE as total fish/day Compute cumulative catch prior to each day What would the following graph look like? 2 Abundance
Concept Depletion Estimate CPE Cumulative Catch 3 Abundance
Development Depletion Estimate Define (along with N0, Nt, Ct, and q) Kt-1 = cumulative catch prior to time t i.e., Key relationship Substitute CPE equation for Nt and simplify What type of function is this? 4 Abundance
Development Depletion Estimate Use regression to fit linear model q = -slope N0 = intercept/q 5 Abundance
Proportion Caught As noted in CPUE module, q is proportion of population caught with one unit of effort but only if effort is small (and then it is only an approximation). q is an instantaneous rate that must be converted to an actual rate with 1-e-q If q=0.02 then 1-e-0.02 = 0.0198 If q=1.00 then 1-e-1.00 = 0.0632 6 Abundance
Class Exercise Do First Question 7 Abundance
Leslie Model Assumptions The population is closed. Catchability (q) is constant. All fish are equally vulnerable to capture method. CPE is substantially reduced by fish removal. Catches remove more than 2% of population. Units of effort are independent - i.e., the individual units of capture method do not compete with each other. 8 Abundance
K-pass Removal Common in stream work Several passes through an area are made Number of fish captured are counted Captured fish are physically removed Derivation of estimates is complex. Zippin and Carle-Strub methods are common Carle-Strub somewhat more general 9 Abundance
Class Exercise Do Second Question 10 Abundance
