The promises and pitfalls of including decadal- scale climate forcing of recruitment in groundfish stock assessment Melissa A. Haltuch and André E. Punt Abstract: Concurrent declines in demersal fish stock abundances and shifts in long-term average environmental conditions have been well documented in the Pacific. Management advice ignoring environmental forcing of recruitment may cause stocks to be over- or under-harvested, so it is important to consider including environmental forcing on recruitment in stock assessment models. Simulation testing is used to determine the statistical power of stock assessments to identify long-term, decadal-scale environmental forcing of recruitment and the ability to estimate management reference points when the dura- tion of the fisheries time series is equal to or less than the period of the environmental cycle. Commonly used assessment methods generally lead to lower total type I (incorrectly rejecting the null hypothesis of no environmental impact) and type II (failing to detect an environmental impact when such a relationship exists) error rates. The promise of integrating environ- mental data with decadal-scale variability directly into stock assessments via the stock–recruitment relationship is out- weighed by the pitfall of high type I error rates that are due to fishing-induced stock declines that coincide with directional environmental change. However, the impact of type I errors can be minimized by choosing an appropriate combination of assessment method and reference point estimators. Résumé : On a bien étudié les déclins des stocks de poissons démersaux et les changements concurrents dans les moyennes à long terme des conditions environnementales dans le Pacifique. Les avis de gestion qui ne tiennent pas compte du forçage environnemental du recrutement peuvent causer une surexploitation ou une sous-exploitation des stocks; il est donc impor- tant de considérer l'inclusion du forçage environnemental dans les modèles d'évaluation des stocks. Des tests de simulation nous servent à déterminer la puissance statistique des évaluations de stocks à identifier le forçage environnemental du recru- tement à long terme à l'échelle des décennies, ainsi qu'à estimer les points de référence de gestion, lorsque la durée de la sé- rie chronologique des pêches est égale ou inférieure à la période du cycle environnemental. Les méthodes d'évaluation couramment utilisées mènent généralement à des taux globaux réduits d'erreurs de type I (le rejet incorrect de l'hypothèse nulle d'absence d'impact environnemental) et de type II (non détection d'un impact environnemental existant). La possibilité d'intégration des données environnementales avec une variabilité à l'échelle des décennies directement dans les évaluations de stocks à travers la relation stock–recrutement est contrebalancée par le piège de forts taux d'erreurs de type I qui sont dus aux déclins des stocks causés par la pêche qui coïncident avec des changements environnementaux directionnels. Cepen- dant, l'impact des erreurs de type I peut être minimisé en choisissant une combinaison appropriée de méthode d'évaluation et d'estimateurs des points de référence. [Traduit par la Rédaction] Introduction Evidence for environmentally forced changes in marine populations has been observed across trophic levels (Brodeur and Ware 1992; Clark et al. 1999) via synchronous changes in the size of multiple populations due to recruitment events (Hollowed et al. 1987; Beamish et al. 1994) and shifts in pro- duction (Adkison et al. 1996; Hare et al. 1999). During the past few decades, many fish stocks have declined in abun- dance because of heavy fishing pressure, but some lightly fished and unfished stocks have also declined (Mueter et al. 2002), suggesting that environmental forcing is playing a role. Models that can resolve the relative impact of fishing and environmental forcing on changes in fish stocks are needed. Typical age-structured fish stock assessments may incorporate environmental forcing into natural mortality, growth, or the stock–recruitment relationship to reflect changes in productivity and carrying capacity. Fisheries oceanographers and stock–recruitment modelers have been working towards linking environmental forcing to recruitment, often with limited success (Myers 1998). While much environment–recruitment modeling has focused on sal- mon, owing to the ability to directly measure spawning bio- mass and recruitment, and small pelagic species, owing to Received 19 October 2010. Accepted 2 March 2011. Published at www.nrcresearchpress.com/cjfas on 17 May 2011. J22076 Paper handled by Associate Editor Carl Walters. M.A. Haltuch. Northwest Fisheries Science Center, NMFS, NOAA, 2725 Montlake Boulevard East, Seattle, WA 98112, USA. A.E. Punt. School of Aquatic and Fishery Sciences, Box 355020, University of Washington, Seattle, WA 98195-5020, USA. Corresponding author: M.A. Haltuch (e-mail: Melissa.Haltuch@noaa.gov). 912 Can. J. Fish. Aquat. Sci. 68: 912–926 (2011) doi:10.1139/F2011-030 Published by NRC Research Press Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by UNIV OF WASHINGTON LIBRARIES on 05/30/11 For personal use only.