Abstract
Recent observations of record low winter sea-ice coverage and warming water temperatures in the eastern Bering Sea have signaled the potential impacts of climate change on this ecosystem, which have implications for commercial fisheries production. We investigate the impacts of forecasted climate change on the eastern Bering Sea food web through the end of the century under medium- and high-emissions climate scenarios in combination with a selection of fisheries management strategies by conducting simulations using a dynamic food web model. The outputs from three global earth system models run under two greenhouse gas emission scenarios were dynamically downscaled using a regional ocean and biogeochemical model to project ecosystem dynamics at the base of the food web. Four fishing scenarios were explored: status quo, no fishing, and two scenarios that alternatively assume increased fishing emphasis on either gadids or flatfishes. Annual fishery quotas were dynamically simulated by combining harvest control rules based on model-simulated stock biomass, while incorporating social and economic tradeoffs induced by the Bering Sea’s combined groundfish harvest cap. There was little predicted difference between the status quo and no fishing scenario for most managed groundfish species biomasses at the end of the century, regardless of emission scenario. Under the status quo fishing scenario, biomass projections for most species and functional groups across trophic levels showed a slow but steady decline toward the end of the century, and most groups were near or below recent historical (1991–2017) biomass levels by 2080. The bottom–up effects of declines in biomass at lower trophic levels as forecasted by the climate-enhanced lower trophic level modeling, drove the biomass trends at higher trophic levels. By 2080, the biomass projections for species and trophic guilds showed very little difference between emission scenarios. Our method for climate-enhanced food web projections can support fisheries managers by informing strategic guidance on the long-term impacts of ecosystem productivity shifts driven by climate change on commercial species and the food web, and how those impacts may interact with different fisheries management scenarios.
Highlights
Climate change is rapidly affecting marine species and ocean ecosystems worldwide (Hoegh-Guldberg and Bruno, 2010; Poloczanska et al, 2013) by warming water temperatures, increasing stratification, reducing dissolved oxygen, and altering nutrient supplies and thereby primary production (Bopp et al, 2013; Boyce and Worm, 2015; Cheng et al, 2019)
We developed an Ecopath with Ecosim model (EwE1, Christensen and Pauly, 1992; Christensen and Walters, 2004) of the eastern Bering Sea to investigate the potential impacts of forecasted climate change on species and the food web, and the interactive effects of different fisheries management scenarios and climate change on modeled outcomes
Our modeling approach was to use the outputs from multiple earth system models, each run under a selection of climate change scenarios, to drive a regional ocean and biogeochemical model (Figure 1)
Summary
Climate change is rapidly affecting marine species and ocean ecosystems worldwide (Hoegh-Guldberg and Bruno, 2010; Poloczanska et al, 2013) by warming water temperatures, increasing stratification, reducing dissolved oxygen, and altering nutrient supplies and thereby primary production (Bopp et al, 2013; Boyce and Worm, 2015; Cheng et al, 2019). Recent years (2014–2019) have seen a decline in the duration and coverage of seasonal sea-ice, a decrease in the size of the cold pool, and warming water temperatures (Stabeno and Bell, 2019; Baker et al, 2020; Danielson et al, 2020) These physical changes altered the phenology, magnitude, and species composition of the phytoplankton bloom and zooplankton community, changes which were transmitted up the food web to forage fishes, including the juvenile stages of commercial species, and to other higher trophic level predators (Sigler et al, 2016; Duffy-Anderson et al, 2019; Lomas et al, 2020). 1ecopath.org which are protected species or whose well-being is thought to be an indicator of food web status (Sydeman et al, 2017)
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