Fig 1 -

Left. Artic Circle view of the northern hemisphere showing the nine sea Ice Regions considered in analysis. Dashed circle shows Arctic Circle delineation. Right. Top Row: Snow crab total exploitable biomass index by Stock Region (AK = Alaska, NL = Newfoundland & Labrador, sGSL = Southern Gulf of St. Lawrence). Second Row: Maximum sea ice extent index by snow crab Stock Region. Third Row: Cod biomass index by snow crab Stock Region. Fourth Row: Annual Arctic Oscillation and North Atlantic Oscillation Indices. Bottom Row: Annual Pacific Decadal and Southern Oscillation Indices. Map source file “The Blue Marble” modified from and credited to NASA Earth Observations (https://neo.gsfc.nasa.gov/view.php?datasetId=BlueMarbleNG-TB). Snow crab distribution is related to seasonal ice cover. Globally, areas either perpetually or ephemerally covered in sea ice do not support large stock biomasses. In cases where exceptions occur, such as in the southernmost (ice-free) extent of the Atlantic Canadian stock range (Nova Scotia), direct cold water inputs from adjacent ice-covered ecosystems occur (Petrie and Drinkwater, 1993). In recent decades, increased ice free periods in Arctic Regions have enabled habitat shifts for snow crab. Numerous recent observations of increasing abundances or first occurrences in Arctic waters (i.e. north of 66.56°N) such as the Chukchi [2], Beaufort [3], Barents [4]), Kara [5], and East Siberian and Laptev Seas [6] collectively confirm that the distribution of snow crab is now near-circumpolar and that the species should no longer be characterized as sub-Arctic.</p

Pearson cross-correlations with total exploitable biomass (tonnes) versus sea ice and climate system indices (North Atlantic Oscillation, NAO; Southern Oscillation, SO; Pacific Decadal Oscillaion, PDO) as well as cod biomass indices (tonnes) by Stock Region (Alaska, AK; Newfoundland and Labrador, NL; southern Gulf of St. Lawrence, sGSL).

Pearson cross-correlations with total exploitable biomass (tonnes) versus sea ice and climate system indices (North Atlantic Oscillation, NAO; Southern Oscillation, SO; Pacific Decadal Oscillaion, PDO) as well as cod biomass indices (tonnes) by Stock Region (Alaska, AK; Newfoundland and Labrador, NL; southern Gulf of St. Lawrence, sGSL).</p

Future Habitat Model (FHM) outputs by Ice Region (Total Arctic [TotArc], Arctic Ocean [ArcOcn], Canadian Archipelago [CanArch], Huddon Bay [Hudson], East Greenland [EGreen], Barents and Kara Seas [BarKara], Baffin Bay and Newfoundland & Labrador [BaffNL], Southern Gulf of St. Lawrence [sGSL], Bering Sea [Bering], and Seas of Okhotsk and Japan [OkhJpn]).

Predictor terms are calendar month, Arctic Oscillation (AO) and carbon dioxide (CO2). edf refers to effective degrees of freedom, Ref.df refers to reference degrees of freedom, and dev.expl. refers to deviance explained.</p

Future habitat model (FHM) of predicted versus observed values of ice extent by Ice Region and year.

Future habitat model (FHM) of predicted versus observed values of ice extent by Ice Region and year.</p

Short-term prediction model of biomasses for Alaska (AK), Newfoundland & Labrador (NL), and southern Gulf of St. Lawrence (sGSL) stock units.

Black squares are survey indices (2020 in Alaska is model estimate). Black lines and dots and associated error bars are full model fits (short-, mid-, long-term effects) and red lines and dots and error bars are model run with no short-term effects. Shaded areas are 95% confidene intervals of model fits.</p

Contour plots of smoothed interaction effects on stock biomasses for short, mid, long-term effects for each stock region (Alaska, AK; Newfoundland and Labrador, NL; southern Gulf of St. Lawrence, sGSL) in the Short-Term Prediction model (STPM).

Short-term effects are Arctic Oscillation at 0 and 1 year lags, Mid-term effects are Arctic Oscillation at 7 and 8 year lags, and long-term effects are sea ice extent at lags of 11, 12, and 13 years. Black dots depict observed data values.</p

Short-term Prediction Model (STPM) outputs by snow crab Stock Region (AK refers to Alaska, NL refers to Newfoundland & Labrador, and sGSL refers to Southern Gulf of St. Lawrence).

Long term predictor terms are for effects on stock biomasses at lag periods of 10–13 years, mid-term predictor terms are for lag periods of 2–9 years, and short-term predictor terms are for lag periods of 0–1 years. Ice refers to ice extent and AO refers to Arctic Oscillation. Numerics next to Ice and AO refer to lag years. edf refers to effective degrees of freedom, Ref.df refers to reference degrees of freedom, and dev.expl. refers to deviance explained.</p

Historic data on monthly ice extent values from NOAA satellite observations by Ice Region (black dots) with Future Habitat Model fits (black lines) and 95% confidence intervals (gray shades).

Blue and red lines show projections under best and worst case CO2 emissions scenarios respectively. Red and blue shaded areas represent bootstrapped 95% prediction intervals. Data are fit by month with calendar years restricted to those indicated on the x-axis. Vertical solid black lines show January and vertial dashed black lines show December. Horizontal green line on Total Arctic panel (top panel) shows 1 million square kilometres ice coverage level.</p

Observed (black) versus predicted (red) ice extent (million km²) by month from 1980 to 2020 by Ice Region.

Observed data are from NOAA satellite observations and predicted ata are from the Future Habitat Model. Horizontal lines and associated 95% confidence intervals are loess regression curves fit to the data for visual assessment of mean trends. Maximum Ice Regions refer to those consistently full of ice during the calendar year, Minimum Ice Regions refer to those consistently fully deplete of ice during the calendar year, and Variable Ice Regions refer to those neither consistently full nor deplete of ice during the calendar year.</p

Fig 8 -

Left. Marginal effect smooths of monthly ice extent patterns by Ice Region. Right. Contour plots of smoothed interaction effects of atmospheric CO2 concentration and the Arctic Oscillation on ice extent in the Future Habitat Model (FHM).</p