Seasonal thermal habitat use and bathymetric distribution of burbot in Tanada and Copper Lakes, Alaska

Abstract

Burbot Lota lota are a cold water, benthic, primarily piscivorous species that inhabits lakes and rivers throughout their Holarctic distribution. Habitat requirements for Burbot are still poorly understood, in part due to the disregard this species has received in fisheries management plans. From June 2009 through September 2011, I investigated the seasonal movements and bathymetric distribution of Burbot in Tanada and Copper lakes, Alaska, using archival tags programmed to record water depth and temperature. One hundred and forty Burbot (70 in each lake) were surgically implanted with archival tags, and 1 year later fish were recaptured to retrieve the archived data (Tanada Lake: 15 fish; Copper Lake: 9 fish). During the ice-out period in spring (mid-May through June), Burbot initiated a migration to the littoral zone (mean depth = 10.72 m; mean internal temperature = 9.4°C). In the summer months (July and August) when lakes were stratified and photoperiod was nearly constant, Burbot occupied the thermocline (mean depth = 7.28 m; mean internal temperature = 12.1°C). During fall months prior to the ice-up period (September and October), occupancy depth shifted to the profundal zone (mean depth = 22.09 m; mean internal temperature = 6.3°C). Under the ice, Burbot remained in the profundal zone and a putative spawning period was observed during February and March when Burbot from both lakes migrated from the profundal zone to ≤ 5 m in depth (mean internal temperature = 2.1°C). Throughout the year Burbot displayed a pattern of diel vertical movements with activity levels peaking during crepuscular hours. However, during the summer when photoperiod was nearly constant, Burbot were relatively sedentary, with only 22% of depth records indicating movement (changes in depth ≥ 1 m). Results from this study indicate that photoperiod and water temperature were highly correlated with seasonal depth occupancy and activity levels in Burbot.