Proceedings of the Fifth National NMFS Stock Assessment Workshop

– Decision tables provide a simple and systematic summary of the consequences of alternative management policies or decisions given various possible true, but generally unknown, states of nature. Decision tables are especially useful for evaluating the precautionary properties of those decisions, as they require explicit consideration of a variety of “what if” possibilities, some of which could be associated with otherwise inadvertent overfishing. Often this approach helps to identify robust solutions, that is, solutions that inherently tend toward desirable outcomes and away from undesirable outcomes. This paper uses the theme of decision tables to evaluate a variety of fishery problems that are significant in their own right. Catch per unit effort (CPUE) remains a popular metric of stock abundance despite having a documented and dangerous tendency toward insensitivity to changes in true abundance. A simple decision table analysis of production model behavior demonstrates that a policy of first squaring raw CPUE has desirable precautionary properties and confers a robustness to production model assessments, whereas use of untransformed CPUE risks overfishing and stock depletion. Use of spawning potential ratios (SPRs) is widespread in stock assessment and development of management policies. The practice of using spawning biomass as a metric of spawning potential can result in overfishing if reproductive value is differentially larger for older fish, e.g., due to multiple spawning or increasing relative fecundity with age. Similarly, some stocks may exhibit an increasing natural mortality rate with age, which appears in assessments as a dome-shaped selectivity curve when the natural mortality rate is assumed to be constant. Decision table analysis of resulting SPRs shows that in this case it is precautionary to assume that natural mortality rate is constant. Some stocks exhibit low frequency patterns in recruitment variability, leading to boom-and-bust cycles over periods of decades. If there is evidence that recruitment strength is correlated with environmental factors, such as mean sea surface temperature, decision table analysis shows that it is precautionary to use the environmental correlate to adjust target fishing rates. Accurate prediction of recruitment strength is of little benefit if the management policy is static. The benefit arises from adjusting the management policy; failure to adjust fishing rates to long periods of low productivity leads to overfishing and stock depletion. Rarely recruiting species pose especially difficult problems for management. One possible mechanism generating rare large recruitments arises from serial correlation in the sequence of survivorship events encountered during the early life history of a fish species. A power function probability density function (pdf) is consistent with the distribution of recruitment strengths of the bocaccio rockfish. A consequence of this pdf is that the underlying stock-recruitment relationship may not be knowable even from extensive data sets. A biomass reserve is a fixed quantity of biomass that is set aside before applying conventional management, such as a fixed harvest rate, on the remainder. Decision table analysis shows that use of a biomass reserve results in near-optimal fishery performance over a wide range of harvest rates.