The Council requested the Independent Scientific Advisory Board (ISAB) to provide a review of the biological and economic impacts of native and non-native predators, the effectiveness of predator management control efforts currently implemented, and the potential impacts on the Columbia River Basin (Basin) from the introduction and spread of northern pike. The request included six science questions and two initial economic questions. This report addresses the science questions. The Council obtained the assistance of economists, who will address the economic questions in a separate companion report.
Review approach.
Brief answers to the Council’s questions
What information is needed to develop a common metric of impact across all predator species? To measure the impact of predation, we need to know (1) the total predation by a predator at each point in time or space where predation occurs; (2) the subsequent predation by all other predators at each point in time or space; and (3) the cumulative survival probability over the full life cycle of the fish or to a consistent point of reference (e.g., Bonneville Dam). An ecosystem-wide, multi-predator, multi-prey approach must be taken to fully understand predation impacts.What type and level of effort are needed? A system-wide, ecosystem-based approach for assessing and managing fish, avian, and pinniped predators collectively will create a more effective and consistent framework for developing and implementing control actions. Assessing impacts of all potential predators throughout the Basin will require integrated analytical tools, such as life-cycle models for salmon and steelhead, measurement of SARs, and density dependence analysis. This type of analysis would allow managers and policymakers to identify (a) locations where life stages of prey species are most susceptible to different predators and (b) the relative benefits of decreasing salmonid mortality at different life stages, making control efforts more biologically and economically effective.Would additional predator management be effective in improving focal species survival? Can we rank predator impacts and then rank which current management activities would be most effective in reducing impacts? Do we know what level of suppression (exploitation) is needed to reduce the northern pike population in Lake Roosevelt to a level sufficient to reduce risk of emigration? Based on the inexorable invasion by northern pike downstream over the past 65 years, it is likely that even with the best efforts in public education, early detection, and control or eradication, pike will eventually invade the anadromous zone. There is no simple estimable relationship between abundance and the probability of emigration from Lake Roosevelt because, for example, each individual female pike produces tens of thousands of eggs so emigration by even one male and one female pike could produce thousands of juveniles. Moreover, evidence indicates that about as many invasions have been caused by illegal stocking, often to distant locations, as by dispersal of pike themselves. It is essential to develop a monitoring program throughout the anadromous zone and a rapid response program to eradicate new invasions at their earliest stages when it may be possible. After populations become established, control efforts will need to be extensive, river-wide, and must continue indefinitely to be successful in reducing mortality of focal salmonids. Suppression in Lake Roosevelt could reduce risks of downstream establishment by reducing the number and (average) body size of downstream dispersers.What are the likely ecological impacts of northern pike should they enter the Basin’s anadromous waters? In this review, the ISAB made a number of conclusions regarding predation management and specific predator species in the Basin:
A coupled ecosystem/socioeconomics approach to predation management and metrics. ISAB 2016-1 ), compensatory mortality is the most important uncertainty to address when developing predation metrics or management plans. Compensatory mortality occurs when predation mortality at one life stage is offset to some degree by decreased mortality at the same or subsequent life stages. The costs and benefits of invasive species prevention, control, and eradication are critical to making sound policy decisions—including the ways in which people’s behavior can promote or frustrate those efforts. Given these high levels of uncertainty and often novel ecological interactions, quantitative evaluation of alternative management or policy responses is sometimes not possible, but a potential approach will be described in the forthcoming economic report.
Northern pikeminnow.
Northern pike.
Other non-native fish.
Avian predation.
Marine mammals.
Evaluating effectiveness.
An altered ecosystem.
