Incorporating Uncertainty into Fishery Models

Consideration of Uncertainty in Stock Assessment of Atlantic Menhaden

D. S. Vaughan, M. H. Prager, and J. W. Smith

doi: https://doi.org/10.47886/9781888569315.ch7

Abstract.—Stock assessments of Atlantic menhaden are conducted annually for the Atlantic States Marine Fisheries Commission, as required by the recently updated Fishery Management Plan, adopted in 1992. Uncertainties in stock assessments have been explored over the years from many perspectives. Two general areas of analysis are considered here. The first area is largely deterministic and concerns the virtual population analysis (VPA), including development and coherence of the catch-at-age matrix; historical retrospective problems; implications of assuming constant M at all ages analyzed; and reliability of recruitment estimates relative to fishery-independent juvenile abundance indices when used for calibrating the VPA. The second area of consideration comprises stochastic analyses, including stochastic projections based on biological benchmarks determined from yield-per-recruit and spawning-stockbiomass- per-recruit models; bootstrapped application of a surplus-production model; and projections from that production model. Nonetheless, the largest uncertainty in assessment of the stock stems not from modeling considerations, but is a biological question: Can the high stock levels observed in the 1950s be regained by reducing fishing mortality? Projections based on production modeling assume that they can, but if exogenous forces (for example, habitat loss or pollution) have affected the stock, it may be that they cannot. If the recent pattern of lower fishing mortality rates in response to social and economic factors continues, the fishery will in essence conduct an experiment that may answer the question.