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April-June 2006
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Status of Stocks & Multispecies Assessment Program

National Stock Assessment Workshop

Martin Dorn and Grant Thompson of the Status of Stocks and Multispecies Assessment (SSMA) Program attended the NMFS National Stock Assessment Workshop in San Francisco, held mid-April 2006. Abstracts from their presentations follow.

Pollock is Green! Adventures in MSC Certification of Walleye Pollock

In April 2005, Gulf of Alaska walleye pollock became the first federally managed fishery to be certified to meet the Marine Stewardship Council’s (MSC) environmental standard for a well managed and sustainable fishery. While certification programs are relatively recent in fisheries, similar programs are well established in forestry and organic farming. The MSC’s certification program has expanded rapidly since its inception in 1999, and other federally managed fisheries are likely to enter into MSC assessment in the future. The paper gave an overview of the MSC certification program and discussed some of the issues that proved contentious with the walleye pollock certification. It is hoped that the experience gained will be beneficial as other fisheries undergo the MSC certification process.

For the extended abstract and further information, please contact Martin Dorn at

By Martin Dorn

A Decision-Theoretic Approach to Ecosystem-Based Fishery Management

Our study concerned “ecosystem-based fishery management” in the sense that it included consideration of: 1) both target and nontarget species; 2) both consumptive and nonconsumptive values; 3) both systematic and stochastic (process error) interactions between species; and 4) both biomass estimation and parameter estimation error.

The study was conducted in four stages. Stage 1 assumed purely deterministic dynamics and known true values for all parameters and variables. The level of risk aversion did not affect the optimal fishing mortality rate, because no uncertainty existed. Stages 2 and 3 added process error and biomass estimation error (in the “management strategy evaluation” sense). The objective function was obtained in closed form. The optimal fishing mortality rate varied inversely with the level of risk aversion (the optimal fishing mortality rate for the risk-neutral case was identical to the Stage 1 optimum). Except for the risk-neutral case, the optimal fishing mortality rate was shown to depend not only on the means and variances of state variables (as has previously been shown for single-species applications) but also on covariances between state variables. Stage 4 added parameter estimation error. Parameter values and covariances were estimated via the Kalman filter. Here, it was no longer possible to obtain the objective function in closed form. The results for Stage 4 were not always straightforwardly related to those of the other stages, because parameter estimates differed from the true values.

For the extended abstract and further information, please contact Grant Thompson at

By Grant Thompson

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