Climate and weather factors affecting winter sheltering by shoreline Copper Rockfish Sebastes caurinus in Howe Sound, British Columbia

We monitored winter sheltering behavior of Copper Rockfish (Sebastes caurinus) in layered boulders at a shoreline in British Columbia and identified possible links to climate change and evolutionary adaptation. During late autumn and winter, these fish were inside the interstices of the boulder pile (termed “winter sheltering”); these fish were actively swimming above the boulders during spring through early fall. Sheltering duration did not vary between normal and most El Niño years (154–177 days). Sheltering longer than 6 months occurred during strong La Niña winters (197–241 days). Additionally, the proximate stimulus for entry into sheltering was intense Arctic outflow windstorms. Emergence from sheltering appears linked to water temperatures, occasionally related more to spring river flooding (snowmelt). The winter sheltering behavior we describe may be unique to shoreline populations in inland seas. Sheltering may confer a fitness advantage by conserving energy or reducing mortality from predation, thus increasing longevity and chances for successful reproduction. Our observations suggest that an ONI threshold of 0.8 °C or greater would be better suited than the current 0.5 °C threshold used to define ONI events.