scholarly journals Sensitivity analysis of the multispecies virtual population analysis model parameterized for a system of trophically-linked species from the eastern Bering Sea

2004 ◽  
Vol 30 (2) ◽  
pp. 285-296 ◽  
Author(s):  
J. Jurado-Molina
Keyword(s):  
Sensitivity Analysis ◽  
Bering Sea ◽  
Population Analysis ◽  
Analysis Model ◽  
Eastern Bering Sea ◽  
Virtual Population Analysis ◽  
Virtual Population

scholarly journals Testing the stability of the suitability coefficients from an eastern Bering Sea multispecies virtual population analysis

2005 ◽  
Vol 62 (5) ◽  
pp. 915-924 ◽  
Author(s):  
Jesús Jurado-Molina ◽  
Patricia A. Livingston ◽  
Vincent F. Gallucci
Keyword(s):  
Stomach Content ◽  
Bering Sea ◽  
Population Analysis ◽  
Data Set ◽  
Predator Species ◽  
Eastern Bering Sea ◽  
Virtual Population Analysis ◽  
Virtual Population ◽  
Total Data ◽  
The Stability

Abstract Suitability coefficients are important for the estimation of predation mortality in a multispecies virtual population analysis (MSVPA) and subsequent use in the multispecies forecasting model (MSFOR). Testing the assumption of the stability of the suitability coefficients is important in assessing the robustness of the predictions made with MSFOR. We used different statistical methods to partially test this assumption for the eastern Bering Sea MSVPA model with eight species, using stomach content data for the years 1985–1989. Comparison of the estimates from two different sets of stomach content data (set one with all data and set two mainly with data from 1985) suggested that the differences between the two types of estimates were much reduced when the number of predator stomachs sampled increased. In a second approach, we contrasted the residual variances of partial data sets with the results from the fit of the total data set. Results suggested a small increase (∼10.8%) in the variation of the suitability coefficients. Comparison of the means of the suitability coefficients associated with each predator species suggests that only 13 of the 50 possible pairwise contrasts were significantly different (α = 0.05). In general, results suggested that the predator preferences and prey vulnerabilities remained stable over the time period studied. Therefore, MSFOR could be considered as a tool to advise fisheries managers within a multispecies context.

Incorporating predation interactions in a statistical catch-at-age model for a predator-prey system in the eastern Bering Sea

2005 ◽  
Vol 62 (8) ◽  
pp. 1865-1873 ◽  
Author(s):  
Jesús Jurado-Molina ◽  
Patricia A Livingston ◽  
James N Ianelli
Keyword(s):  
Bering Sea ◽  
Stock Assessment ◽  
Population Analysis ◽  
Adult Population ◽  
Single Species ◽  
Virtual Population Analysis ◽  
Virtual Population ◽  
Statistical Assumptions ◽  
The Difference ◽  
Management Advice

Virtual population analysis and the statistical catch-at-age methods are common stock assessment models used for management advice. The difference between them is the statistical assumptions allowing the fitting of parameters by considering how errors enter into the models and the data sources for the estimation. Fishery managers are being asked to consider multispecies interactions in their decisions. One option to achieve this goal is the multispecies virtual population analysis (MSVPA); however, its lack of statistical assumptions does not allow the use of tools used in single-species stock assessment. We chose to use a two-species system, walleye pollock (Theragra chalcogramma) and Pacific cod (Gadus macrocephalus), to incorporate the predation equations from MSVPA into an age-structured multispecies statistical model (MSM). Results suggest that both models produced similar estimates of suitability coefficients and predation mortalities. The adult population estimates from the single-species stock assessment and MSM were also comparable. MSM provides a measure of parameter uncertainty, which is not available with the MSVPA technologies. MSM is an important advancement in providing advice to fisheries managers because it incorporates the standard tools such as Bayesian methods and decision analysis into a multispecies context, helping to establish useful scenarios for management in the Bering Sea.

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.

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.

Separable Virtual Population Analysis of Pacific Salmon with Application to Marked Chinook Salmon, Oncorhynchus tshawytscha, from California's Central Valley

1987 ◽  
Vol 44 (6) ◽  
pp. 1213-1220 ◽  
Author(s):  
Robert G. Kope
Keyword(s):  
Chinook Salmon ◽  
Goodness Of Fit ◽  
Oncorhynchus Tshawytscha ◽  
Pacific Salmon ◽  
Population Analysis ◽  
Central Valley ◽  
Virtual Population Analysis ◽  
Virtual Population ◽  
California's Central Valley ◽  
California’S Central Valley

A separable virtual population analysis model is developed for Pacific salmon which utilizes aged catch and spawning escapement data. This model is applied to marked chinook salmon, Oncorhynchus tshawytscha, from California's Central Valley hatcheries using weighted least squares criteria for goodness of fit. Structural inadequacies of the model apparently produce discrepancies between predicted values and observed data that are of about the same magnitude as the observational errors in estimating the recoveries of marked fish. Some of the inadequacy of the model may be due to environmentally induced variability in population parameters, but for the marked fish used in this analysis, some of the variability is probably due to year-to-year variability in hatchery practices. From this analysis it appears that although nominal fishing effort has been relatively stable or even declining in recent years, fishing mortality has been increasing with the exception of 1983 and 1984.

Sign in / Sign up

Export Citation Format

Share Document