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Chilean Chilean jack jack mackerel mackerel stock stock - - PowerPoint PPT Presentation
Chilean Chilean jack jack mackerel mackerel stock stock - - PowerPoint PPT Presentation
Chilean Chilean jack jack mackerel mackerel stock stock assessment assessment m odel Cristian Canales (ccanales@ifop.cl) y Rodolfo Serra Cristian Canales (ccanales@ifop.cl) y Rodolfo Serra Instituto de Fomento Pesquero (IFOP) - Chile Stock
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Stochastic Stochastic modeling modeling
- There
are error sources in the data collection. Then, this information is an imperfect representation of the population
- This approximation implies to assume different likelihood functions
for modeling, for example, the observation error
- The Chilean jack mackerel assessment is done considering this
type of approximation
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Information and indexes Ej CPUEobs Data collection Previous knowldge Population dynamics model Observation model Parameters (θ)
Stochastic Stochastic modeling modeling
- Ej. CPUEpred = G(x,y,z,θ)
Error model f=G(CPUEpred – CPUEobs) f minimum ? no
End
(Maximum Likelihood)
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Information Information employed employed
- Estimates of growth, maturity, and natural mortality (M=0.23) parameters.
- Landings for the northern and central-southern fleets (1975-2007).
- Age at catch (2 - 12+ years) matrices per fleet/zone. The length
compositions data from ex-URSS fleet, were assumed to be similar to the data collected in the central southern zone of Chile.
- Average weight at age matrices.
- Average weight at age matrices.
- Age compositions from the acoustic cruises (1997-2006) in the central-
southern zone.
- Acoustic biomass (1997-2007).
- Spawning biomass indices estimated by the Daily Egg Production Method
(DEPM) (1999- 2001; 2003-2006).
- CPUE for the central-southern purse seine fleet (1996-2003).
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Space Space considerations considerations
- There
is an age-specific migration process, from northern Chile towards central- south area. This is a gradual process that occur when the fish have 4-5 years
- ld
2 3 4 5 6 7 8 9 10 11 12 2 4 6 x 10
5
Northern zone
Catch-at-age
- This
means that, in the northern area, the older fish are less available for
- exploitation. Complementary,
in the central-south area the fish are full exploitated since 7 years old
2 3 4 5 6 7 8 9 10 11 12 2 4 6 8 10 x 10
5
Age (year) Southern zone
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Main Main modelling modelling considerations considerations Selectivity Selectivity
Northern Northern area area
2 2
) ( 2 1 ,
t t
a s f t a
e S
µ − −
=
Southern Southern area area
1 ) 19 ln( ,
%, 50
1
− ∆ − −
+ =
t f t
f a a f t a
e S
1 North 2 4 6 8 10 12 0.2 0.4 0.6 0.8 Age (year) Selectivity South
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Main Main modelling modelling considerations considerations Acoustic Acoustic catchability catchability hypothesis hypothesis Bc
c=qc * B
* B 1) 1) Change Change in in distribution distribution: :
1 exp log ˆ
y c y i y
B q n B =
∑
2) 2) Contraction Contraction of
- f biomass
biomass: : 2) 2) Contraction Contraction of
- f biomass
biomass: :
2002 1 exp log ˆ [5 400] 2002 ˆ [5 200]
y i y y c y y y
y B B mn n B q y B B mn
λ
η < ∈ − = ≥ ∈ −
∑
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Main Main results results
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Main Main results results
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Testing Testing hypotesis hypotesis
Hypotesis SSB (ton) SSB/SSBo
- log Like
p AIC S1=Distribution change 4,807,400 0.2697 4,360 61 8842 S2= Contraction
- f biomass
distribution 4,083,400 0.2418 4,372 63 8871
SSB: Spawning biomass, SSBo: Virginal Spawning biomass, -log Like: - log likelihood, p: parameters number, AIC: Akaike information criterion
Even in the most optimistic of cases (S1), the population is reduced Even in the most optimistic of cases (S1), the population is reduced to a level lower than is recommendable (SSB/ to a level lower than is recommendable (SSB/SSB SSBo=0.4) =0.4)
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