Sub-Arctic no more: Short- and long-term global-scale prospects for snow crab (Chionoecetes opilio) under global warming

Abstract

Snow crab is a sea-ice associated species that supports several economically important fisheries in northern latitudes. During the past decade considerable stock range changes have occurred, characterized by a general shift from sub-Arctic ecosystems into the Arctic. We developed predictive models for short-term biomass trajectories and long-term habitat potential under a changing climate. Sea ice extent and the Arctic Oscillation were important variables in the short-term models. Future sea ice extent was used as an analog for long-term habitat potential and was predicted as a function of projected atmospheric carbon dioxide concentrations and the Arctic Oscillation. Our results show that global scale snow crab habitat and biomass are currently at or near historically measured highs. Similar overall habitat potential to historic and current levels is expected to continue out to 2100 under best case CO2 scenarios but declines below historic levels are projected to begin after about 2050 under worst cast CO2 scenarios. In the short-term, most historical stock ranges are expected to maintain productive fisheries while new habitats open. In the long-term, under all CO2 scenarios, we project a shift in habitats from historic ranges into new frontiers as sea ice recedes. Future population trajectories depend upon the ability of snow crab to track habitat shifts and we discuss possible forthcoming changes in context of potential socioeconomic outcomes.

Merits of Multi-Indicator Precautionary Approach Management in a Male-Only Crab Fishery

“…The pCPUE model is a generalized additive mixed model fit in the mgcv package [45] in R. It regresses standardized fishery CPUE (st_cpue) against predictor variables of fishery ERI, the twoyear moving average EBI (BIO) from trawl surveys (1995-2017) or an average of trawl plus trap surveys (2018-2023), an annual index of the North Atlantic Oscillation (NAO) from seven years prior (NAO7), and random effects of AD and year, treated as a factor variable Equation (4). NAO7 is included due to the strong positive correlation of future exploitable biomass with this climate system at lags of 6-8 years [14,46]. A thin-plate smoothing spline (s) is included on all fixed effects, with the exception of ERI.…”

“…Exploitable biomass levels in NL snow crab are strongly affected by both climate and fishing. There is strong climatic control of resource productivity through mechanisms such as water temperature, atmospheric forcing, and sea ice [46]. Despite warm conditions helping promote large individual size, overall, cold conditions are most favorable for sustained high productivity of this cold water specialist [49,50].…”

“…NL snow crab are predominately 9-11 years old when they reach legal size, with crab in the exploitable biomass typically 9-13 years of age [44]. Thus, positive impacts of cold conditions during early ontogeny can become evident at lags of a decade or more, and the mid-life benefits of cold conditions can exacerbate realized outcomes [46]. As an extension of this, climate forcings along the NL marine shelf tend to oscillate at roughly decadal time scales [51]; thus, oscillating patterns in resource trajectory can be predictable using long-and mid-term ontogenetic climate variables, such as occurred preceding the forecasted mid-late 2010s decline [11,12].…”

“…Increased extraction efficiency helps foster increased sustainability in fisheries management and is advantageous in a scenario of a resource decline. In this regard, it is important to highlight that a decline in the EBI is anticipated in the short term, with the most recent assessment showing declines in pre-recruit crab [33] and a long-term prognosis for reduced habitat as greenhouse effect warming ensues [46]. This multi-indicator PA system cannot stop a resource decline, but there are measures in place to prohibit excessive exploitation, such as those that occurred under reduced biomass in the late 2010s, if and when the resource does decline.…”