An evaluation of the role of top piscivores in the fish community of the main basin of Lake Huron

Stocking of hatchery-reared fish has been widespread in Lake Huron since the mid-1960's, representing the majority of recruitment for several key predator populations including the introduced chinook salmon and the native lake trout. With recruitment dominated by hatchery plants, natural limitations on recruitment may not be able to prevent predator populations from exceeding the capacity of the forage base. Exceeding forage fish capacity can reduce predator growth, negatively affect predator survival, and delay or impair predator reproductive capabilities. The purpose of my research was to improve our understanding of the forage demand by the key predators in Lake Huron. This was accomplished by analyzing the temporal and spatial characteristics of the caloric content of Lake Huron fish species, using bioenergetics models coupled with age-structured stock assessment models to estimate annual population consumption, projecting future forage demand under different management scenarios; and parameterizing a functional response model for the dominant predator, chinook salmon.; The key predators in the open waters of the main basin of Lake Huron are burbot, lake trout, chinook salmon, and walleye. Estimates of their combined forage demand averaged nearly 36 million kg annually between 1996 and 1998. During this time, lake trout and chinook salmon were the major consumers, accounting for 74% of the total consumption of prey fish by the key predators. Based on estimates of prey abundance, consumption by the key predators may be approaching prey capacity, supported by recent evidence of declines in predator growth. Projections of forage demand resulting from various management actions suggest that changes to chinook salmon stocking and reductions in sea lamprey-induced mortality have significant effects on predator forage demand.; A functional response model relates the number of prey eaten to prey abundance. We used this model to explore how changes in prey abundance affect consumption and growth. Our functional response model suggested that variations in total consumption and growth have been only weakly tied to measured prey abundance. Age 1–4 chinook salmon were feeding above 60% of their maximum rate of consumption and variations in prey abundance explained little of the variation in observed growth. Model fitting results suggest that the decline in chinook salmon growth between 1974 and 1998 cannot be explained by variations in prey abundance so observed declines in growth must be related to other factors. (Abstract shortened by UMI.)...