Brackish-water residency and semi-anadromy in Arctic lake trout (Salvelinus namaycush) inferred from otolith microchemistry

Lake trout, Salvelinus namaycush, are considered a freshwater species but have been documented using brackish and marine water environments in the Arctic in a semi-anadromous manner. The objective of this study was to describe lake trout life histories present in the brackish waters of Husky Lakes, Northwest Territories (NT) using otolith strontium (Sr) profiles obtained by Laser Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICP-MS). Lake trout from Husky Lakes and Noell Lake (freshwater), NT were sampled by spring hook-and-line angling and open water gillnetting in 2000-2004, 2009 and 2012 by local subsistence fishers as part of a larger ecological assessment. Harvested fish were sampled for biological data and tissue samples including otoliths. The otoliths were prepared for line scan analysis of Sr from the core region to the outer edge by LA-ICP-MS. Sr profiles were evaluated visually suggesting the presence of two life histories within Husky Lakes, semi-anadromy (14%, n = 8) and brackish-water residency (86%, n = 50). The visual classification of life histories was supported using generalized linear mixed effects modeling indicating that a minimum of two distinct ecosystems (fresh and brackish water) were used during early life by lake trout from Husky Lakes. Otolith Sr profiles also show that the majority of Husky Lakes lake trout sampled (86%) spawn and spend their entire lives in the brackish waters of Husky Lakes. These are the first data to support an entirely brackish-water resident life history for lake trout.