Abstract
<p>The northern stock of black sea bass Centropristis striata has greatly expanded in recent decades and now occurs abundantly in most Northwest Atlantic (NWA) coastal waters from spring to fall. During winter, this species still migrates offshore to avoid waters below their presumed thermal limit (similar to 6 degrees C), but the fitness benefit of this strategy diminishes as inshore waters warm and migration distances to suitable (>10 degrees C) overwintering habitat shrink. We conducted 2 overwinter experiments on black sea bass juveniles to simulate their thermal experience of migrating offshore (19 to 12 to 14 degrees C) or remaining within Long Island Sound (LIS) during an exceptionally warm winter (2022-2023: 18 to 5 to 12 degrees C), documenting their survival, growth, and lipid accumulation. Overwintering inshore caused only minor reductions in survival (100 to 84%), led to no loss in lipid reserves, but incurred a growth cost compared to conspecifics in the offshore experiment. We then coupled downscaled CMIP6 climate models to LIS winter air temperature records, projecting mean LIS winter temperatures to increase from 3.2 degrees C (1991-2023 baseline) to 4.8 degrees C by 2050-2060 (SSP5-8.5), and the average time below 6 degrees C to decrease from 95 to 68 d. A separate shelf model projected the rapid northward movement of the 10 degrees C isotherm in February bottom temperatures on the NWA shelf, thereby reducing the minimum overwinter migration distance from currently similar to 600 to similar to 120 km by 2055. Inshore overwintering will become increasingly feasible for black sea bass, perhaps leading to partial migration patterns and further poleward range expansion.</p>