Disentangling the effects of climate, abundance, and size on the distribution of marine fish: an example based on four stocks from the Northeast US shelf

ICES Journal of Marine Science ICES Journal of Marine Science (2015), 72(5), 1311– 1322. doi:10.1093/icesjms/fsu217 Original Article Disentangling the effects of climate, abundance, and size on the distribution of marine fish: an example based on four stocks from the Northeast US shelf Richard J. Bell 1*, David E. Richardson 1, Jonathan A. Hare1, Patrick D. Lynch 2, and Paula S. Fratantoni3 1 Northeast Fisheries Science Center, National Marine Fisheries Service, Narragansett, RI 02882, USA Office of Science and Technology, National Marine Fisheries Service, Silver Spring, MD 20910, USA 3 Northeast Fisheries Science Center, National Marine Fisheries Service, Woods Hole, MA 02543, USA 2 *Corresponding author: tel: +001 401 782 3368; fax: +001 401 782 3201; e-mail: Bell, R. J., Richardson, D. E., Hare, J. A., Lynch, P. D., and Fratantoni, P. S. Disentangling the effects of climate, abundance, and size on the distribution of marine fish: an example based on four stocks from the Northeast US shelf. – ICES Journal of Marine Science, 72: 1311 – 1322. Received 14 February 2014; revised 30 October 2014; accepted 1 November 2014; advance access publication 11 December 2014. Climate change and fishing can have major impacts on the distribution of natural marine resources. Climate change alters the distribution of suitable habitat, forcing organisms to shift their range or attempt to survive under suboptimal conditions. Fishing reduces the abundance of marine populations and truncates their age structure leading to range contractions or shifts. Along the east coast of the United States, there have been major changes in fish populations due to the impacts of fishing and subsequent regulations, as well as changes in the climate. Black sea bass, scup, summer flounder, and winter flounder are important commercial and recreational species, which utilize inshore and offshore waters on the northeast shelf. We examined the distributions of the four species with the Northeast Fisheries Science Center trawl surveys to determine if the along-shelf centres of biomass had changed over time and if the changes were attributed to changes in temperature or fishing pressure through changes in abundance and length structure. Black sea bass, scup, and summer flounder exhibited significant poleward shifts in distributions in at least one season while the Southern New England/Mid-Atlantic Bight stock of winter flounder did not shift. Generalized additive modelling indicated that the changes in the centres of biomass for black sea bass and scup in spring were related to climate, while the change in the distribution of summer flounder was largely attributed to a decrease in fishing pressure and an expansion of the length– age structure. While the changes in ocean temperatures will have major impacts on the distribution of marine taxa, the effects of fishing can be of equivalent magnitude and on a more immediate time scale. It is important for management to take all factors into consideration when developing regulations for natural marine resources. Keywords: Black Sea bass, climate, distribution shifts, fishing, Mid-Atlantic Bight, scup, summer flounder, winter flounder. Introduction Increasing global temperatures can have major impacts on marine organisms, including shifts in distributions and changes in abundance (Walther et al., 2002; Hare et al., 2010; Pinsky et al., 2013. Recent studies have shown that with the poleward shift in ocean temperature isotherms (Burrows et al., 2011) there has been a subsequent shift both poleward and to greater depths in marine taxa (Pinsky et al., 2013; Poloczanska et al., 2013). Organisms increase their overall survival and fecundity by occupying, to the extent possible, their optimal habitat (Anderson et al., 2013). Individuals within their optimal habitat maximize their overall fitness and minimize their mortality risks. Climate change, however, can affect certain aspects of an organism’s habitat. The physical structure or photoperiod may remain constant at a given location or latitude, but other habitat components such as temperature, salinity, dissolved oxygen, and advection may be altered (Anderson et al., 2013). Shifts in distribution are then the result of individuals attempting to remain within the best conditions possible, through migration or declines in abundance in suboptimal environments, while expanding in better suited environments, if they exist. # 2014 International Council for the Exploration of the Sea. Published by Oxford University Press. All rights reserved. For Permissions, please email: 1312 In addition to climate-mediated changes in distribution, range shifts may also be caused by simple changes in overall abundance. When populations are low, they occupy the highest quality habitat available. As the population density increases, individuals move out into formerly inferior habitat where intraspecific competition is lower (MacCall, 1990; Quinn and Deriso, 1999). Habitat quality is rarely isotropic, so the areal expansion of the population along a habitat gradient with increasing abundance could result in a shift in distribution. Changes in abundance due to increases in mortality can also affect distribution through changes in the length –age structure of a population. Within certain species, such as Pacific hake, there is a tendency for individuals to be distributed by size, with larger members at higher latitudes (Nelson and Dark, 1985; Smith et al., 1992). Fishing preferentially removes the largest and oldest fish (Fenberg and Kaustuv, 2008). For stocks segregated by size, fishing pressure could remove the larger individuals, which, if located at higher latitudes, would result in a truncation of the species range and a distribution centred at a lower latitude. Along the Northeast Shelf of the United States there have been major shifts in the distribution of marine taxa (Nye et al., 2009; Lucey and Nye, 2010; Howell and Auster, 2012; Pinsky and Fogarty, 2012). Changes in the species assemblages due to the shifts can have major impacts on ecosystem goods and services. The distribution shifts are particularly important because the catch quota for a number of stocks and therefore peoples livelihoods, are allocated based on the species’ distributions in previous decades (ASMFC, 2004). Understanding the mechanisms which regulate distribution must be taken into account as part of any potential change to the quota allocation system. On the Northeast shelf there is evidence of warming water temperatures (Nixon et al., 2004; Friedland and Hare, 2007; Belkin, 2009) and large changes in the abundance of fish species due to fishing and recovery (Fogarty and Murawski, 1998; Terceiro, 2012b). Many of the studies on species distribution shifts have implicated increasing temperature as a major driver. However, changes in size and age structure (Radlinski et al., 2013) and changes in abundance (Hare et al., 2010) have also been implicated in distribution shifts in (...truncated)