Seasonal fishery dynamics of a previously unexploited rainbow trout population with contrasts to established fisheries

Although predator-prey interactions between anglers and fish populations are well studied and understood, little is known about whether these interactions differ between lightly and fully exploited populations. Furthermore, within-season shifts in catch rates are poorly understood. These differences have been thought to be due in part to changes in fish behavior after catch and release, which reduces the overall catchability of the population. To address these questions, angling was introduced to a previously unexploited population of rainbow trout Oncorhynchus mykiss and the within-season fishery dynamics were contrasted with those of fully exploited populations. We found that catch rates rapidly decreased after the introduction of angling; moreover, once this had occurred, angler effort decreased. Catch per unit effort (CPUE) and catchability of the lightly exploited population, were initially quite high compared with most exploited populations but quickly decreased throughout the summer to levels similar to those of fish populations that have been open to angling for decades. Therefore, the differences in catch rates are transitory and the unexploited population quickly becomes indiscernible from fully exploited populations. Seasonality in CPUE was observed in all lakes, with significant decreases in CPUE throughout the summer. These changes in CPUE reflected changes in catchability throughout the season. Although the relative effects of harvest and possible behavioral shifts in fish after catch and release accounted for some variation in catchability, the effects were insufficient to explain total seasonal decreases in catchability in the previously unexploited population. These findings demonstrate that any potential shifts in fish behavior subsequent to catch and release are inadequate to explain seasonal shifts in catch rates. Apparently, seasonal changes in CPUE are driven more by ecological processes than by the fishery.