Fisheries Research 147 (2013) 10–23 Contents lists available at ScienceDirect Fisheries Research jou rn al hom ep age: www.elsevier.com/locate/fishres Evaluating alternative methods for monitoring and estimating responses of salmon productivity in the North Pacific to future climatic change and other processes: A simulation study Brigitte Dorner a,b,∗ , Kendra R. Holt a,1 , Randall M. Peterman a , Chris Jordan c , David P. Larsen d , Anthony R. Olsen e , Omar I. Abdul-Aziz f,2 a School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada b General Delivery, Lasqueti Island, British Columbia V0R 2J0, Canada c NOAA Fisheries, c/o U.S. Environmental Protection Agency, 200 SW 35th St., Corvallis, OR97333, USA d Pacific States Marine Fisheries Commission, c/o U.S. Environmental Protection Agency, 200 SW 35th St., Corvallis, OR 97333, USA e Western Ecology Division, National Health and Environmental Effects Laboratory, U. S. Environmental Protection Agency, 200 SW 35th Street, Corvallis, OR 97333, USA f School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195-5020, USA a r t i c l e i n f o Article history: Received 4 July 2012 Received in revised form 25 March 2013 Accepted 26 March 2013 Keywords: Salmon monitoring Climate change Confounding Sampling design Productivity changes Stock assessment Ocean conditions a b s t r a c t We used empirically based simulation modelling of 48 sockeye salmon (O. nerka) populations to examine how reliably alternative monitoring designs and fish stock assessment methods can distinguish between changes in density-dependent versus density-independent components of productivity and identify the relative contribution of a climate-driven covariate. We explored a wide range of scenarios for ocean and freshwater conditions and the response of salmon productivity (adult recruits per spawner) to those conditions. Our results show that stock assessments based on historical relationships between salmon productivity and climate-driven oceanographic conditions will likely perform poorly when those rela- tionships change, even when such changes are anticipated and incorporated into stock assessment models in a timely manner. Estimating the relative importance of climate-driven oceanographic influences as a driver of sockeye productivity will be difficult, especially if climatic changes occur rapidly and concur- rently with other disturbances. Thus, better understanding of the mechanisms by which climatic changes and other drivers influence salmon productivity may be essential to avoid undesirable management out- comes. As well, an expansion of monitoring of juvenile salmon abundances on more salmon stocks is needed to help distinguish the effects of different drivers. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Given the prospects for future climatic change and other pressures on salmon habitat, salmon (Oncorhynchus spp.) popula- tions that inhabit the Northeastern Pacific Ocean face an uncertain future. Forecasts suggest that salmon from the west coast of North America will generally encounter warmer sea-surface temper- atures (SSTs) and different marine conditions than in the past ∗ Corresponding author. Tel.: +1 250 333 8849; fax: +1 250 333 8849. E-mail addresses: bdorner@driftwoodcove.ca (B. Dorner), kendra.holt@dfo-mpo.gc.ca (K.R. Holt), peterman@sfu.ca (R.M. Peterman), chris.jordan@noaa.gov (C. Jordan), larsen.phil@epa.gov (D.P. Larsen), olsen.tony@epa.gov (A.R. Olsen), oabdulaz@fiu.edu (O.I. Abdul-Aziz). 1 Current address: Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Rd., Nanaimo, British Columbia, Canada V9T 6N7. 2 Present address: Department of Civil and Environmental Engineering, Florida International University, 10555 W. Flagler Street, EC3602, Miami, FL 33174 USA. (IPCC, 2007). As well, previously documented decreasing trends in productivity for sockeye salmon (O. nerka) stocks ranging from Washington to Southeast Alaska (Peterman and Dorner, 2012) are consistent with, and may be linked to, unfavorable habitat con- ditions associated with climatic changes. However, the impacts of climatic change are likely complex and potentially confounded with other impacts on productivity caused by existing or future changes to spawning, rearing, and migration habitats, which have also predominantly affected stocks in the southern part of the species’ distribution (Marmorek et al., 2011). A good understand- ing of the relative importance of different causal factors potentially affecting salmon productivity is a key step towards an appropriate management response to current and potential future declines in productivity. Correlations between past indices of salmon productivity and coastal SST encountered by juveniles have been well documented (Mantua et al., 1997; Mueter et al., 2002a), and SST is there- fore a likely candidate for an environmental covariate that can be 0165-7836/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fishres.2013.03.017