Author: Brett Michael Johnson

Publisher:

Published: 1993

Total Pages: 480

ISBN-13:

Tradicionaly recreational fishery management has focused on dynamics of individual fish populations. Attempts to improve fish populations center on manipulations of harvest or the population itself. However, outcomes of fishery management actions have been difficult to forecast. Ecological processes within fish communities and angler responses can produce unanticipated effects. This thesis documents my research on these processes in Lake Mendota to make fishery management a more holistic, predictive science. A food web manipulation began in 1987. This project used several fishery management tools to increase the biomass of piscivorus gamefish to evaluate food web manipulation as a water quality management tool. Forecasting and measuring direct and indirect effects of the manipulation were important objetives. To forecast how management would affect piscivore populations, and their consumption of prey, I combined two computer models: an age-structured population model and a bioenergetics model. This technique predicted how size, abundance, and consumption of piscivores changed with stocking rates and sire limits. A walleye stocking program that yielded 8,000 yearling/year doubled consumption demand; adding a 381-mm minimum size limit achieved another 50% increase. To predict consequences of piscivore management for prey populations, I studied predador and prey fish populations. Highley variable prey recuitment made forecasting impacts of piscivory difficult. Based on historic recruitment patterns, enhanced walleye populations could consume 65-100% of young-of-year perch biomass produced in low recruitment years. When recruitment was high walleyes consumed less than 5% of the biomass. Translating predicted piscivore consumption into perch dynamics was accomplished by incorporating prey recruitment uncertainty. Angler response to piscivore enhancements was intense. Angler effort increased four-fold and harvest rates doubled to 60% per year. As a result, forescasts of piscivore consumption demand and the effectiveness of food web manipulation dependend heavily on responses of sport anglers to piscivore populations. Hence, a better understanding of angler dynamics was required before ecological effects of fishery management actions could be predicted. I developed a predatory-prey model to study angler-piscivore interactions. This approach linked angler and fish dynamics, and provided the means to incorporate fish, anglers, and management actions within one framework.