Assessment of the lake whitefish fishery in Michigan waters of Lake Huron.

Abstract

Catch and catch per unit of effort (CPUE) data for lake whitefish (Coregonus clupeaformis) in Michigan waters of Lake Huron were analyzed with autocorrelation analysis to test for time lags and to develop forecasting equations. A 4-year time lag, corresponding to the age at maturity, was found for lake whitefish catch and CPUE. Relations among lake whitefish catch as well as CPUE, and environmental and biological data were investigated with cross correlation analysis. Cross correlation analysis indicated that lake whitefish catch was negatively correlated with freezing degree days; catch and CPUE were negatively correlated with monthly air temperature and sea lamprey abundance in previous years; catch was positively correlated with fishing effort in the present year and one year later; CPUE was positively correlated with fishing effort one year later. A new delayed reproduction time lag model was proposed and compared with the Schaefer model and the transitional delayed reproduction lag model developed by Hutchinson (1948). Three models coupled with sea lamprey predation were fitted to catch and effort data. The proposed delayed reproduction time lag model with a variable population growth rate and catchability coefficient gave the best description of the lake whitefish fishery. Simulations indicated that a reproductive time lag, fishing, and sea lamprey predation had large effects on lake whitefish populations. A bioenergetic population simulation model that coupled Larkin's predator-prey model, Ursin's bioenergetic growth model, Ivlev's feeding equation, and the exponential mortality mode was used to simulate the lake whitefish fishery and to examine the population compensation processes. Simulations with random food concentrations, age specific mortality, size dependent recruitment and maturity, and sea lamprey predation best described the observed yields. As fishing mortality increased, the abundance of fish decreased, size of individuals increased, maturity occurred at an earlier age, and more eggs were produced per individual. Analysis with the net reproductive rate showed that mortality before maturity and age at maturity were the two parameters that have the largest potential for compensation.