Quiz 7 Flashcards
(38 cards)
Ways to estimate pop size (Depletion methods)
- fishing effort and catch rate
- works if vulnerability is uniform and constant overtime with no additions/losses over the study interval
Leslie method
- assumes # of fish caught per unit effort in time is proportional to the # of fish present at the beginning of t
- qN_t = C_t/f_t
- C/f is CPUE
- q = a catchability coeffiecient
- N = population before depletion
DeLury’s method
- based on assumption that the pop is closed and the CPUE @ N_inf
- assumes pop declines proportionally with total effort
- N_t = N_inf(e^-qE_t)
- E_T is total cumulative effort
Recruited to the gear
-when a fish grows large enough to be vulnerable to a particular gear
Recruits to a fishery
-assumes that similar gear is used throughout the fishery
Recruitment
-individual fish survives into a defined life stage
Steady stable population
-pop births = death
Exponential decay model
dN/dt = -zN
z is coefficient of instantaneous mortality
Catch curve
- estimates z from data
- assumes mortality is relatively constant from one age class to the next
- works best on post-juvenile fish
z variable
-total instantanous mortality
=F+M
F = fishing mortality
M = natural mortality
A variable
-total annual mortality
= 1 - S = 1 - e^-z
Weighted formulas
- assume recruitment is equal from one year to the next
- equal survival rates
- equal vulnerability to the sampling gear
Heinke’s formula
-used with its hard to determine the age of older fish
= (N(all age class) - N(youngest))/N(all age class)
How are early life stages of fish vulnerable
-they can starve, be eaten, damaged by turbulent eddies
Match-mismatch hypothesis
-suggested that the match or mis match of larval fish occurring together with their food determined whether they fed or starved
Bigger is better hypothesis
-larger larvae have a better chance of avoiding predators
Metrics for characterizing fish within a pop: Size characteristics
- total length
- fork length
- standard length
- Weight (wet or dry)
Fulton’s condition factor
K = W/L^3 * 100,000
Relative weight
W_t = W/W* W* = weight predicted from length/weight relationship
GSI
-gonadsomatic index
= W_gonads/W_body
Models of growth: von Bertalanffy growth curve
L_t = L_inf(1-e^(-K(t-t_0))) L_t = length at time t L_inf = theoretical max length K = growth coefficient t_0 = theoretical age at L = 0 -graph begins at orgin and increase exponentially to an asymptote
Weight equivalent of von Bertalanffy growth curve
-sigmoidal curve
Ford-Walford plot
-estimates parameters L_inf and K
L_(t+1) = L_inf (1-e^-K) + L_t*e^-K
-assumes that t_0 is 0
Gompertz model
-looks at growth within the year which isn’t done by the von B. model
