Seasonal and Diel Bathythermal Distributions of Lake Whitefish in Lake Huron: Potential Implications for Lake Trout Bycatch in Commercial Fisheries

Abstract

AbstractDepths and temperatures recorded during 2003–2005 by archival tags implanted in Lake Whitefish Coregonus clupeaformis and in Great Lakes origin (GLO) and New York Finger Lakes origin (FLO) strains of Lake Trout Salvelinus namaycush were used to compare seasonal diel depth and temperature distributions in Lake Huron. Seasonal depth distributions were examined to determine if species differences could be exploited to reduce bycatch of Lake Trout in commercial Lake Whitefish gill‐net fisheries. Both GLO and FLO Lake Trout used deeper and colder waters than Lake Whitefish during daylight and dark. Temperature differences between species were greatest during periods of stratification when behavioral thermoregulation was possible. Other than during spawning periods, the greatest depth and temperature separation occurred in late July between FLO Lake Trout (37.0 m; 6.5 ºC) and Lake Whitefish (25.1 m; 10.2 ºC). If maximum depths of gill nets were regulated seasonally to between 25 and 35 m, ≥ 50% of the Lake Whitefish population would be vulnerable while avoiding 89% or more of Lake Trout. Lake Trout percentages targeted under such regulations would be lowest in late July (GLO = 8% and FLO = 11%) and early August (GLO = 4% and FLO = 7%). However, archival tags measure fish depth and not location or bottom depth, and modal depths of gill‐net effort for Lake Whitefish (38 to 57 m) exceeded those from the Lake Whitefish archival tag data. This discrepancy suggests that many Lake Whitefish might be pelagic above the reach of bottom‐set gill nets, so depth restrictions could be less effective in reducing Lake Trout bycatch than suggested by our data. A further implication is that use of gill nets suspended above the bottom to target pelagic Lake Whitefish could also reduce bycatch while potentially increasing Lake Whitefish harvest.Received August 19, 2015; accepted February 21, 2016 Published online June 28, 2016