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

Abstract

15We analyzed monitoring data from small Boreal Shield lakes to understand how 16 variations in air temperature and precipitation affect the phenology and amount of habitat for 17 lake trout (Salvelinus namaycush). Annual air temperatures increased by ~2 ºC (significant in 18 fall and winter). In response, ice-cover was reduced by ~19 d. Despite earlier ice-offs, springs 19 became longer, allowing lake trout longer access to littoral regions when water temperatures 20 were cool. Although summer surface water temperatures increased, the summer did not 21 lengthen. Instead, later spring-warming and fall-cooling of lakes caused summer to shift later in 22 the year, potentially delaying fall spawning. Complete loss of optimal oxythermal habitat volume 23 occurred in all lakes and became more prevalent over time, moreso in the darkest lakes. 24Although air temperatures did not become more variable, several habitat measures did, 25 including mean summer surface water temperatures, duration of ice-cover, timing of ice-off, and 26 minimum volumes of optimal oxythermal habitat. Our results suggest that future warming will 27 impose greater thermal stress on lake trout, but may be tempered by longer springs. 28 29

Behavioral responses to annual temperature variation alter the dominant energy pathway, growth, and condition of a cold-water predator

“…This behavior also has been exhibited by other temperaturesensitive fish, including brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss), which have been documented to stop foraging and seek cool-water refuge when temperatures exceed their thermal preferences (30,31). Therefore, continued warming of surface-water temperatures during the summer (15,16) could extend periods of limited littoral access in salmonids, increasing their reliance on pelagic-derived energy.…”

“…At least in our study system, the fall does not seem to be a period when lake trout make extensive use of littoral resources. Based on the apparent limited acquisition of littoral energy in summer and fall periods, it appears that the spring period, which is strongly influenced by climate (16), is critical for the annual growth and condition of lake trout.…”

“…Recent studies have shown that lake-surface temperatures have risen globally over the past 30 y (15), with north-temperate lakes also having longer open-water seasons and undergoing shifts in the phenology of seasonal water temperatures (16). These observed changes in lake temperatures suggest that future warming may alter littoral-pelagic coupling by mobile predatory Significance Climate warming is having wide-ranging effects on aquatic ecosystems.…”

“…1) (13,14,18,19). We hypothesized that because of the direct influence of temperature on fish physiology, annual changes in the phenology of littoral zone water temperatures, which are closely linked to air temperature variations (16), would influence littoralpelagic coupling by lake trout (Fig. 1).…”

The impact of a loss of hydrologic connectivity on boreal lake thermal and evaporative regimes

“…). Over the past four decades, the ice‐free period has increased by ∼ 19 d for lakes at the IISD‐ELA (Guzzo and Blanchfield ), with regional predictions of 10, 17, and 29 more ice‐free days in the 2020s, 2050s, and 2080s, respectively (Keller ). Applying the evaporation rates documented in this study, extended ice‐free seasons would result in an additional 35 mm, 60 mm, or 100 mm of seasonal evaporation.…”