Spawning and early life-history characteristics of bull trout in a headwater-lake ecosystem

Abstract

Bull trout, Salvelinus confluentus, are in decline throughout their native range. Interaction with nonnative species is considered to be one of the drivers of bull trout decline. Bull trout exhibit a variety of life-history strategies and lacustrine-adfluvial bull trout seem to be particularly susceptible to population decline when nonnative lake trout, S. namaycush, invade or are introduced into lakes where bull trout are the dominant salmonid. Quartz Lake in Glacier National Park, Montana, provided a unique opportunity to gather information on the spawning and early life-history characteristics of a bull trout population prior to anticipated declines in bull trout abundance due to lake trout invasion. The objectives of this study were (1) to characterize the spatial and temporal dynamics of bull trout spawning migrations and associate areas of high redd accumulation to abiotic factors, and (2) to quantify the influence of abiotic factors on the distribution of subadult bull trout in tributary streams of Quartz Lake. Stream surveys were conducted to quantify physical habitat characteristics in the study area, backpack electrofishing was used to sample subadult bull trout rearing in lake tributaries, and redd surveys were used to investigate the spatial and temporal trends in the accumulation of bull trout redds. Bull trout redds and subadult bull trout were found throughout the study area; however, bull trout spawning and rearing appeared to be concentrated in lower Quartz Creek. This area was low gradient, and there was a high percent of gravel and cobble substrates. Bull trout spawning began in late September, peaked in early October, and concluded in mid-October. These data provide important information on bull trout life-history in headwater lakes and provide biologists with baseline data that will be useful for assessing the effects of lake trout suppression efforts that began in 2009.