Temperature influence on commercial lake whitefish harvest in eastern Lake Michigan

Lake whitefish (Coregonus clupeaformis) support the largest commercial fishery in Lake Michigan, yet relatively little is known of the thermal ecology of free-ranging lake whitefish. In 2000 six commercial trap nets were instrumented with self-recording temperature data loggers to examine the relationship between lake whitefish harvest, water temperature statistics, and fishing effort. Several variables including surface water temperature (SWT), bottom water temperature (BWT), difference between SWT and BWT, and fishing effort were used in both a backward and forward stepwise regression model against fishing harvest. Both the backward and forward results generated similar R-2 statistics of 0.62 and 0.58 respectively, with the backward model suggesting BWT, variance of BWT, and the difference between SWT and BWT as the best regression model. The forward regression results suggested that SWT alone was the best model. Subsequent ANOVA tests support selecting the simpler model for describing the lake whitefish dependence on temperature, which was: y = 21,000e(-0.366T) where y is dressed lake whitefish harvest (kg) and T is SWT (degreesC). This model worked well for surface water temperatures between approximately 10 and 20degreesC The success in describing the fish harvest with surface water temperatures is most likely the consequence of warm surface water intrusions into the hypolimnion from coastal downwellings being the dominant factor controlling lake whitefish distribution.