Morphological and Ecological Variation among Populations and Subspecies of Burbot (Lota lota [L, 1758]) from the Mackenzie River Delta, Canada

Introduction the Burbot (Lota lota [L, 1758]) is a northern fish species with a circumpolar distribution in freshwater rivers, creeks, and lakes. Burbot live in cold lakes and rivers, where they tend to frequent deep water near the bottom (McPhail and Paragamian 2000). they can at tain a length of 1 m and a weight of 8 kg, although most fish are 0.3–0.6 m in length and weigh 1–3 kg (McPhail and Paragamian 2000). the Mackenzie River Delta (northwest territories, Canada) is one of the northernmost ranges of Burbot distribution. In this area, they are fished for their liver and eggs, which are their most valued parts (gwich’in Elders 1999). Recently, there have been increased reports of Burbot with malformations, poor muscle tone, unpleasant tasting flesh, and diseased livers from local and traditional fishers in the gwich’in Settlement area (thompson 2008). this prompted re search by the gwich’in Renewable Resources Board, the data from which are the basis of this study. Burbot are great dispersers and individuals may cover extensive geographic areas, perhaps driven by spawning behaviour and the search for food (McPhail and Paragamian 2000; Slavík et al. 2005). their spawning period ranges from winter (December) until early spring (March), when water is often still covered by ice (gwich’in Elders 1999; McPhail and Paragamian 2000). Little is known about spawning behaviour in nature, but it seems to be polygynous broadcast spawning, as Burbot form spawning aggregations where a few fe males are surrounded by many males (McCrimmon 1959). there is no evidence of sex-biased dispersal based on population genetic analyses (Elmer et al. 2012). Whether Burbot have defined home ranges de pends on their habitat. In lakes, Burbot do not keep stable positions as food availability is low and dispersed, whereas, in rivers, higher food availability permits them to occupy defined home ranges (Slavík et al. 2005). Burbot home ranges are much bigger than those of other temperate freshwater fish, with measured movements of up to 255 km (McPhail and Paragamian 2000). there are two subspecies of Burbot: Lota lota maculosa is restricted to north america and Lota lota lota is distributed across Eurasia and Beringia. Based on population genetic analyses, Elmer et al. (2012) located a precise contact zone between Burbot subspecies in the Mackenzie River Delta. at tsiigehtchic (included in the current study), most individuals collected were L. l. maculosa and upriver of that locality only L. l. maculosa were found. Downstream from tsiigehtchic, all populations in the Mackenzie River Delta were exclusively L. l. lota. therefore, the lower Mackenzie River is where the discrete parapatric distributions of Morphological and Ecological Variation among Populations and Subspecies of Burbot (Lota lota [L, 1758]) from the Mackenzie River Delta, Canada