Climate change alters the quantity and phenology of habitat for lake trout (Salvelinus namaycush) in small Boreal Shield lakes

We analyzed monitoring data (1970-2013) from small Boreal Shield lakes to understand how variations in air temperature and precipitation affect the phenology and amount of habitat for lake trout (Salvelinus namaycush). Annual air temperatures increased by similar to 2 degrees C (significant in fall and winter). In response, ice cover was reduced by similar to 19 days. Despite earlier ice-offs, springs became longer, allowing lake trout longer access to littoral regions when water temperatures were cool. Although summer surface water temperatures increased, the summer did not lengthen. Instead, later spring-warming and fall-cooling of lakes caused summer to shift later in the year, potentially delaying fall spawning. Complete loss of optimal oxythermal habitat volume occurred in all lakes and became more prevalent over time, more so in the darkest lakes. Although air temperatures did not become more variable, several habitat measures did, including mean summer surface water temperatures, duration of ice cover, timing of ice-off, and minimum volumes of optimal oxythermal habitat. Our results suggest that future warming will impose greater thermal stress on lake trout, but may be tempered by longer springs.