Anadromy in Arctic populations of lake trout (Salvelinus namaycush): otolith microchemistry, stable isotopes, and comparisons with Arctic char (Salvelinus alpinus)

Abstract

In the family Salmonidae, lake trout ( Salvelinus namaycush ) are considered the least tolerant of salt water. There are, however, sporadic reports of lake trout in coastal, brackish habitats in the Canadian Arctic. Otolith microchemistry analyses conducted on lake trout and Arctic char ( Salvelinus alpinus ) from four Arctic lakes in the West Kitikmeot region of Nunavut, Canada, revealed that 37 of 135 (27%) lake trout made annual marine migrations. Anadromous lake trout were in significantly better condition (K = 1.17) and had significantly higher C:N ratios (3.71) than resident lake trout (K = 1.05 and C:N = 3.34). Anadromous lake trout also had significantly higher δ15N (mean = 16.4‰), δ13C (mean = –22.3‰), and δ34S (mean = 13.43‰) isotope ratios than resident lake trout (means = 12.84‰, –26.21‰, and 1.93‰ for δ15N, δ13C, and δ34S, respectively); results were similar for Arctic char and agree with results from previous studies. Mean age of first migration for lake trout was 13 years, which was significantly older than that for Arctic char (5 years). This could be a reflection of size-dependent salinity tolerance in lake trout, but further research is required. These are the first detailed scientific data documenting anadromy in lake trout.

Long-distance anadromous migration in a fresh water specialist: the Lake Trout (<em>Salvelinus namaycush</em>)

“…Populations in which ana dromy has previously been documented, however, have been found at very short distances from the marine environment (within 3 km, Swanson et al 2010). Here, we report the capture of two Lake Trout returning from marine waters some 50 km downstream from the closest lake where overwintering and/or spawning would be possible.…”

“…Local knowledge in the Cambridge Bay region indicates that Lake Trout are sometimes caught in marine waters (B. Nakashook, Cambridge Bay resident, personal communication, 2013). Recently, quantitative evidence of anadromy in Arctic populations of Lake Trout has become available to corroborate this local knowledge (Swanson et al 2010) and, combined, these pieces of information indicate that anadromy in this species may not be as rare as once assumed. For instance, in Nauyuk Lake, a system located on the mainland of Canada approximately 90 km southwest of the Halokvik River, 40% of assessed Lake Trout were classified as anadromous (Swanson et al 2010).…”

“…Where anadromy has been confirmed in Lake Trout, migration distances have been relatively short (< 3 km, Swanson et al 2010), suggesting that Lake Trout employing this life history tactic are associated with systems in which the distance to marine waters is short. Here, we describe a case of longdistance migration in anadromous Lake Trout based on observational evidence and capture data accumulated Long-distance Anadromous Migration in a Fresh Water Specialist: the Lake Trout (Salvelinus namaycush) from a fisheries weir assessment on the Halokvik River (locally known as 30 Mile), Victoria Island.…”

“…Lake Trout were typi cally believed to be invariably non-anadromous (Hendry et al 2004), but were recently shown to be able to survive salinities equal to that of full-strength sea water (i.e., 30%, Hiroi and McCormick 2007). Lake Trout have been observed sporadically, although rarely, in marine waters (dating back to the 1950s and reviewed in Martin and Olver 1980), and recent data from otolith microchemistry and stable isotope analyses confirm that some coastal Canadian Arctic populations of Lake Trout do make annual migrations to marine environments (Swanson et al 2010). Among four study populations, 27% of Lake Trout made annual migrations to the sea, and anadromous Lake Trout were in better condition and had lower concentrations of mercury than fresh water resident Lake Trout (Swanson and Kidd 2009;Swanson et al 2010).…”

“…Lake Trout have been observed sporadically, although rarely, in marine waters (dating back to the 1950s and reviewed in Martin and Olver 1980), and recent data from otolith microchemistry and stable isotope analyses confirm that some coastal Canadian Arctic populations of Lake Trout do make annual migrations to marine environments (Swanson et al 2010). Among four study populations, 27% of Lake Trout made annual migrations to the sea, and anadromous Lake Trout were in better condition and had lower concentrations of mercury than fresh water resident Lake Trout (Swanson and Kidd 2009;Swanson et al 2010). Further study using isotope mixing models found that marine prey items constituted a large proportion (66%) of the diet of anadromous Lake Trout (Swanson et al 2011).…”