A General Theory for Analyzing Catch at Age Data

1982 ◽  
Vol 39 (8) ◽  
pp. 1195-1207 ◽  
Author(s):  
David Fournier ◽  
Chris P. Archibald
Keyword(s):  
Maximum Likelihood ◽  
General Theory ◽  
Population Analysis ◽  
Cohort Analysis ◽  
Likelihood Estimation ◽  
Fishing Effort ◽  
Extra Information ◽  
Stochastic Nature ◽  
Virtual Population Analysis ◽  
Virtual Population

We present a general theory for analyzing catch at age data for a fishery. This theory seems to be the first to address itself properly to the stochastic nature of the errors in the observed catch at age data. The model developed is very flexible and accommodates itself easily to the inclusion of extra information such as fishing effort data or information about errors in the aging procedure. An example is given to illustrate the use of the model.Key words: cohort analysis, virtual population analysis, maximum likelihood estimation, aging errors

Virtual Population Analysis (VPA) Equations for Nonhomogeneous Populations, and a Family of Approximations Including Improvements on Pope's Cohort Analysis

1986 ◽  
Vol 43 (12) ◽  
pp. 2406-2409 ◽  
Author(s):  
Alec D. MacCall
Keyword(s):  
Mortality Rate ◽  
Population Analysis ◽  
Seasonal Pattern ◽  
Cohort Analysis ◽  
Natural Mortality ◽  
Close Approximation ◽  
Virtual Population Analysis ◽  
Virtual Population ◽  
Special Case

A set of "backward" virtual population analysis (VPA) equations relates catch (Ct) from continuous fishing between times t and t + 1 to population n size (Nt, Nt+1) when a portion of the stock is unavailable to fishing. The usual VPA equations become a special case where the entire stock is available (i.e. the stock is homogeneous). A close approximation to the VPA equations is Nt = Nt+1 exp(M) + CtM/(1 − exp(−M)), which has properties similar to Pope's "cohort analysis" and is somewhat more accurate in the case of a continuous fishery, especially if the natural mortality rate (M) is large. Much closer simple approximations are possible if the seasonal pattern of catches is known.

On Estimating Partial Recruitment in Virtual Population Analysis

1981 ◽  
Vol 38 (8) ◽  
pp. 1003-1005
Author(s):  
Derek A. Roff
Keyword(s):  
Random Sample ◽  
Population Analysis ◽  
Cohort Analysis ◽  
Population Estimation ◽  
Commercial Catch ◽  
Virtual Population Analysis ◽  
Virtual Population

Virtual population analysis or cohort analysis is hindered by the difficulties of estimating the partial recruitment factors. A method currently used for estimating the latter is the ratio of the frequency of a particular age in the commercial catch to that in a research sample. This method is examined and shown to be only an approximation that may cause significant errors in the analysis. An alternate method, utilizing the same data, is proposed. A method is then given that tests the assumption that the research sample is a random sample from the population.Key words: population estimation, cohort analysis, virtual population analysis, partial recruitment

scholarly journals Virtual population analysis of two snapper species, Lutjanus analis and Lutjanus chrysurus, caught off Pernambuco State, north-eastern Brazil

2009 ◽  
Vol 57 (3) ◽  
pp. 229-242 ◽  
Author(s):  
Sérgio Macedo Gomes de Mattos ◽  
Francesc Maynou
Keyword(s):  
Steady State ◽  
Population Analysis ◽  
Fishing Effort ◽  
Data Series ◽  
Virtual Population Analysis ◽  
Virtual Population ◽  
Eastern Brazil ◽  
North Eastern ◽  
Effort Reduction ◽  
Yield Per Recruit

We applied steady-state Virtual Population Analysis - VPA to two stocks of snappers (Lutjanus analis and L. chrysurus) exploited by artisanal hand-line fleets along the Pernambuco State coast (North-eastern Brazil). We show that even short-data series (1 year of sampling) can produce a useful diagnosis of fisheries resources. Both stocks are slightly overexploited by the hand-line fishery and a higher yield-per-recruit would be obtained by a reduction of effort of 16% for L. analis and 43% for L. chrysurus. Given the impracticability of managing the two stocks separately, we propose a 25% decrease of fishing effort for the hand-line fleet. By incorporating the results of VPA into a simulation framework, we can develop a comparison of the likely result of different policy options (effort regulation) based on 3 simple indicators (Spawning stock biomass-per-recruit, biomass-perrecruit and yield-per-recruit). We compare the results of effort reduction with those of effort increase (25%) through simulation analysis. Allowing for the difficulty of testing assumptions introduced in our model (steady-state, Beverton and Holt recruitment model) and using standard fisheries analysis techniques, we show that useful fisheries advice can be produced even in a context of limited data. Providing advice to developing countries coastal fisheries is an urgent issue, given the high dependence of local communities on coastal living resources and the increasing fishing effort applied by a growing population.

scholarly journals Aspects of Stock Assessment of Klunzinger's Mullet, Planiliza klunzengeri (Day, 1888) from Northwest Arabian Gulf, Iraq

2021 ◽  
pp. 25-36
Author(s):  
Ali H. Al-Hassani ◽  
Abdul-Razak M. Mohamed
Keyword(s):  
Stock Assessment ◽  
Population Analysis ◽  
Arabian Gulf ◽  
Total Mortality ◽  
Landing Site ◽  
Fishing Effort ◽  
Reference Points ◽  
Recruitment Pattern ◽  
Virtual Population Analysis ◽  
Virtual Population

The stock assessment of Klunzinger's mullet, Planiliza klunzengeri was conducted, to estimate its some aspects viz. growth, mortality, recruitment, yield-per-recruit and virtual population analysis in Iraqi marine waters, northwest Arabian Gulf, Iraq, from February 2020 and January 2021. The population parameters were analyzed by the FiSAT software using monthly length-frequency data collected by the Shaheen dhow and from the artisanal fishermen at the fish landing site in Al-Fao city to derive information required for their management. A total of 3319 individuals of P. klunzingeri ranged from 11.0 to 27.0 cm have been collected. Length-weight relationship was calculated as W= 0.026L2.716. The asymptotic length (L∞), growth rate (K) and the growth performance index (Ø') were 29.8 cm, 0.34 and 2.48, respectively. The rates of annual instantaneous of total mortality (Z), fishing mortality (F), natural mortality (M) and present exploitation (Epresent) were 1.19, 0.84, 0.36 and 0.30, respectively. The recruitment pattern of P. klunzingeri was continuous throughout the year, with one peak during May. The results of virtual population analysis revealed that the majority of P. klunzingeri were harvested between 14 cm and 19 cm. The length at first capture (L50) in the current study was higher than the length at first maturity (Lm) of the species in the region. The Epresent was below the biological target reference points (E0.1= 0.770 and Emax= 0.903), referred to the stock of P. klunzingeri is underexploited. Therefore, the harvest level should increase to its maximum sustainable yield level by increasing fishing effort level with monitoring surveys and evaluate the risk associated with fishing effort increases as fishing precautionary approaches.

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