Lake trout (Salvelinus namaycush) distribution and ancestry in the Canadian Maritimes, and a case study of critical habitat and origin in Sherbrooke Lake, Nova Scotia

Lake Trout (Salvelinus namaycush) in New Brunswick and Nova Scotia are an elusive and understudied species, and historical stocking makes it unclear if they are of post-glacial origin. A synthesis of historical naturalist writings and government fish stocking records suggest that Lake Trout are native to this region. Records of Lake Trout, in some lakes, precede the earliest stocking records that began in 1886. Historical documents indicate that Lake Trout were once more widely distributed than they are now, and many populations have likely been extirpated. Sherbrooke Lake in Lunenburg County, Nova Scotia, may contain a native population that was later stocked upon, and contains the only known breeding population of Lake Trout in Nova Scotia. To identify key habitat features of Lake Trout in the lake, acoustic telemetry was used to track the depth and temperature residency of 11 Lake Trout and bathymetric and water column measurements were taken. To determine if Lake Trout are a native species to Sherbrooke Lake, tissue samples of 25 individuals from the lake were used to compare genetic likeness to populations that had been stocked into the lake. During early spring and summer of 2022, Lake Trout in Sherbrooke Lake occupied a hypolimnetic residency. Suitable temperatures of 8.5 to 10 °C were only available in one of three deep basins of the lake. Thermal mixing of the epilimnion, because of Hurricane Fiona, caused the hypolimnion in the south basin to shrink, forcing adult Lake Trout to narrow their depth range for approximately one month. This reduced depth range comprises only ~0.5% of the total volume of Sherbrooke Lake. Genetic analysis concluded that these Lake Trout were the most genetically distinct population evaluated when compared to those from Ontario, Manitoba, New York, and Vermont. DNA results indicate that native, genetically distinct Lake Trout persist in Sherbrooke Lake.