Thermal habitat utilization by northern pike (Esox lucius) in Tadenac Bay, Georgian Bay, Ontario, Canada

Abstract

<p>The northern pike <em>(Esox lucius</em>) is a recreationally and ecologically important top predator fish in the Laurentian Great Lakes, where there are still naturally reproducing populations, especially in the relatively undisturbed eastern arm of Lake Huron, Georgian Bay. I conducted a two-year study in a relatively pristine embayment, Tadenac Bay, located in eastern Georgian Bay to determine 1) how thermal habitat suitability changes both seasonally and annually and 2) how radio-tagged northern pike utilize different thermal habitats. During May and June in both years, water temperatures throughout the water column were favourable (13-21°C) for growth of northern pike adults, but during July and August, the surface to 5m was often above favourable temperatures. Yet in both years, during the middle of July (week 30), individual fish were tracked to areas with temperatures >27°C. During the warmer year (2011), the larger females used significantly deeper habitat (2.89±0.46m SE, n=9) than the smaller males (1.93±0.17m, SE, n=27) (one tailed t-test, t(45)=-2.00, p=0.035). During the cooler year (2012), females used deeper habitat (3.60±0.84m SE, n= 8) compared to males (2.45±0.32m, SE, n= 15) but the means were not statistically significant.</p> <p>A comparison of mean annual water levels of Georgian Bay with variation in global mean surface temperature show that the warmest years to date coincided with sustained low water levels in Georgian Bay since 1999. Global circulation models predict that these warming trends will continue and will lead to further reductions in water levels. Based on a bathymetric model for Tadenac Bay, a drop in water level of 1 m from current levels (2012) would result in 18% loss of existing habitat. The approach used in this study can be applied to other regions of Georgian Bay to quantify current and projected thermal habitat for northern pike.</p>