Fisheries Research 81 (2006) 189–201 Using multi-species surplus production models to estimate ecosystem-level maximum sustainable yields Franz J. Mueter a,∗ , Bernard A. Megrey b a Joint Institute for the Study of the Atmosphere and the Oceans, P.O. Box 354235, University of Washington, Seattle, WA 98115, USA b National Marine Fisheries Service, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, WA 98115, USA Received 12 March 2005; received in revised form 4 July 2006; accepted 26 July 2006 Abstract We used time series of biomass and catches for the major commercial groundfish stocks in the Eastern Bering Sea/Aleutian Islands region and in the Gulf of Alaska to compute annual surplus production for 1977–2004. Annual surplus production and average annual biomass were aggregated across stocks within each region to examine the relationship between total surplus production and total aggregated biomass. We fit two surplus production models (Graham-Schaefer and Pella-Tomlinson) to the observed relationships to estimate maximum multi-species surplus production (equivalent to maximum sustainable yield) of the groundfish complexes in these ecosystems. Maximum multi-species surplus production was estimated to be approximately 2.5 × 10 6 t in the Bering Sea/Aleutian Islands and 330 × 10 3 t in the Gulf of Alaska. These point estimates were smaller than the sum of single-species MSY proxies from recent stock assessments, and estimates for the Gulf of Alaska were much smaller than earlier estimates that were used to specify optimum yield ranges for the Gulf of Alaska groundfish complex. Therefore, optimum yield ranges for the Gulf of Alaska may need to be re-assessed to reflect more recent conditions. We further estimated the effects of environmental variability on annual surplus production using correlations and generalized surplus production models with environmental covariates. Results suggest that surplus production in the Bering Sea may be lower during conditions associated with the positive phase of the Pacific Decadal Oscillation, which is characterized by warmer temperatures, reduced ice, and reduced wind mixing over the shelf. Similarly, surplus production on the Gulf of Alaska shelf was lower during years with warm bottom temperatures coupled with low salinities in late winter. If maximum multi-species surplus production varies as a result of environmental variability, optimum yield ranges for the groundfish complexes in these ecosystems should take such fluctuations into account. © 2006 Elsevier B.V. All rights reserved. Keywords: Graham-Schaefer model; Pella-Tomlinson model; Productivity; Ecosystem-based fisheries management; Bering Sea; Gulf of Alaska 1. Introduction An ecosystem-based approach to fisheries management has become a key goal of national and international institutions. In the United States, two recent ocean commissions have advocated ecosystem-based approaches and the Sustainable Fisheries Act mandates the establishment of an advisory panel “to develop rec- ommendations to expand the application of ecosystem principles in fishery conservation and management activities”. A key objec- tive of any ecosystem approach is maintaining the productivity of fish communities, as well as harvests from those communities, within a desired range. To achieve this objective the North Pacific Fishery Management Council has defined maximum sustainable ∗ Corresponding author. Present address: 697 Fordham Drive, Fairbanks, AK 99709, USA. Tel.: +1 907 479 8815; fax: +1 907 479 8815. E-mail address: fmueter@alaska.net (F.J. Mueter). yield (MSY) and optimum yield (OY) ranges for the groundfish complexes of the Eastern Bering Sea/Aleutian Islands region (BSAI) and for the Gulf of Alaska (GoA). Total removals from both groundfish complexes are required by statute to remain within these ranges, which therefore provide a powerful tool to help prevent ecosystem overfishing. Estimates of system-wide MSY may be obtained by summing single-species MSYs or by estimating a multi-species MSY using multi-species or ecosystem models. Historical estimates of aggregate MSY for the Gulf of Alaska and Bering Sea were based on proxies such as allowable biological catches estimated from stock assessments done in the mid-1980s and summed across all managed stocks (NPFMC, 2005a,b). Early ecosystem models suggested that aggregate MSY may provide a conser- vative estimate of sustainable yields for the BSAI groundfish complex (Laevastu et al., 1982). However, multi-species mod- els (e.g. Collie and Gislason, 2001), ecosystem models (Walters 0165-7836/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.fishres.2006.07.010