Quantifying habitat-dependent mortality risk in lacustrine fishes by means of tethering trials and survival analyses

Habitat features influence the ecological interactions and spatial distribution of fish species. For example, water transparency and macrophyte cover, as well as their interaction, can strongly influence predation risk and mortality. Tethering trials were conducted in Lake St. Pierre (Quebec, Canada) to assess the effects of water transparency and macrophyte cover on the mortality risk of eight abundant fish species; Brown Bullhead (Ameiurus nebulosus), Mooneye (Hiodon tergisus), Emerald Shiner (Notropis atherinoides), Golden Shiner (Notropis crysoleucas), Blacknose Shiner (Notropis heterolepis), Spottail Shiner (Notropis hudsonius), Trout-perch (Percopsis omiscomaycus), and Yellow Perch (Perca flavescens). Kaplan-Meier survival curves showed that mortality risk varied substantially among three groups of species having high, intermediate, or low survival rates. Species with spines appeared to have higher survival rates, consistent with the notion that spines deter predators. Cox regression models showed that mortality risk for six of the eight species was influenced by water transparency or an interaction of transparency with macrophyte cover. Mortality risk was generally greatest at low transparency. Variation in water transparency may generate spatial heterogeneity in fish abundance, either through direct effects, such as local reduction in prey numbers by predation, or indirect effects, such as behavioural avoidance of risky areas by prey.