Abstract
One of the key tasks in current fisheries research is to improve the performance, in terms of accuracy and utility, of projections of recruitment-driven population dynamics in the medium-term. Reliable indications of the median level and variability of recruitment over a five- to ten-year time-scale would be invaluable in the determination of appropriate levels of fishing mortality, in order to attempt to maintain sustainable fish stocks. Building upon the stochastic simulation approach currently adopted within ICES stock assessment working groups, this paper investigates the use of time-series models to characterise the historical development of residuals to fitted stock-recruitment models. We use the probability of SSB (spawning stock biomass) falling below Bpa (precautionary value of spawning stock biomass) over a range of multipliers on imposed fishing mortality as a diagnostic statistic to compare projections. Case studies of commercially-important fish stocks are presented (North Sea cod, haddock and whiting), and the potential implications of the new approaches for fisheries management are discussed.
Highlights
Medium-term projections of age-structured population dynamics are the basis for many strategic management decisions about fisheries within the purview of ICES (International Council for the Exploration of the Sea)
Such projections generally take the form of stochastic simulations of stock performance over a future 10-year time period under a range of levels of imposed fishing mortality F, and are used to determine levels of F that are likely to minimise the risk of stock collapse
The exploitation pressure on most commercially-important species managed via ICES’. Advice is such that few fish survive for longer than five years, and projections are largely driven by the assumed recruitment model and the initial estimated size of the stock
Summary
Medium-term projections of age-structured population dynamics are the basis for many strategic management decisions about fisheries within the purview of ICES (International Council for the Exploration of the Sea). Such projections generally take the form of stochastic simulations of stock performance over a future 10-year time period under a range of levels of imposed fishing mortality F, and are used to determine levels of F that are likely to minimise the risk of stock collapse. Advice is such that few fish survive for longer than five years, and projections are largely driven by the assumed recruitment model and the initial estimated size of the stock. The purpose of this paper is to highlight the principal statistical deficiency in this approach, correct it, and compare the new results with the old for the North Sea cod, haddock and whiting populations
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