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

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.

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

scholarly journals Evaluating the effect of predation mortality on forage species population dynamics in the Northeast US continental shelf ecosystem using multispecies virtual population analysis

2008 ◽  
Vol 65 (9) ◽  
pp. 1689-1700 ◽  
Author(s):  
Megan C. Tyrrell ◽  
Jason S. Link ◽  
Hassan Moustahfid ◽  
William J. Overholtz
Keyword(s):  
Population Dynamics ◽  
Continental Shelf ◽  
Population Analysis ◽  
Northwest Atlantic ◽  
Virtual Population Analysis ◽  
Virtual Population ◽  
Predation Mortality ◽  
Forage Species ◽  
Species Population ◽  
Northeast Us

AbstractTyrrell, M. C., Link, J. S., Moustahfid, H., and Overholtz, W. J. 2008. Evaluating the effect of predation mortality on forage species population dynamics in the Northeast US continental shelf ecosystem using multispecies virtual population analysis. – ICES Journal of Marine Science, 65: 1689–1700. An expanded version of multispecies virtual population analysis (MSVPA) is used to analyse the effects of predation by 14 key predators on Atlantic herring and Atlantic mackerel in the Northwest Atlantic ecosystem for the period 1982–2002. For herring, MSVPA produced greater abundance estimates than single-species assessments, especially for the youngest age classes. The average rate of predation mortality for herring aged 0 and 1 was also higher than the standard total natural mortality rate (0.2) for the 21-year time frame (0.84–3.2). The same was true for mackerel in this MSVPA (0.37–1.6). Consumptive removals of herring and mackerel generally increased over time. From 1999 to 2001, the biomass removed by predators exceeded each species' commercial landings. The sum of consumption and landings notably exceeded the multispecies maximum sustainable yield for herring for the years 1995–2002 and for mackerel for the period 1999–2002. We highlight the importance of accounting for predation on forage species in the context of changes to the fish community that have taken place in the Northwest Atlantic over the past few decades.

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