Seasonal habitat use of white sucker Catostomus commersonii in a small Boreal lake

Abstract White sucker ( Catostomus commersonii ) is a large-bodied benthic fish species that is found across a broad geographic region in North America. Often overlooked, white suckers are an integral component of aquatic ecosystems in their role as the dominant nearshore benthivore in many lakes. Few detailed field investigations on habitat use and thermal occupancy of white sucker exist, limiting our ability to predict the risk of habitat loss from development and climate warming for this cool-water species. Here we investigated seasonal depth, temperature and spatial occupancy patterns of white suckers in a lake located in northern Ontario, Canada. Using a combination of positioning acoustic telemetry and environmental data, we determined depth and space use patterns, seasonal temperature preference indices, and the affinity of white sucker to the lake bottom (i.e., benthic habitat) over a year long period. We found that the white suckers were consistently observed in shallow waters (< 10 m depth) and near the lake bottom across all seasons but were positioned slightly deeper in the winter. The tagged white suckers showed a strong temperature selection preference for thermal habitat between 10 and 16 °C during the open-water seasons and tended to avoid cold (< 6 °C) thermal habitat. Space use patterns, calculated using kernel utilization distributions, and daily movement rates were surprisingly consistent across all seasons, with regular occupancy of only some nearshore areas. This study highlights a highly restrictive pattern of habitat use by white sucker that is consistent across seasons, suggesting that this generalist species may be more vulnerable to anthropogenic disturbance than previously thought.