Proposed Assessment and Decision-Making Framework to Inform Scaup Harvest Management

摘要

Pursuant to a request from the Service Regulations Committee (SRC), we synthesized existing monitoring data, developed an assessment framework, and derived a state-dependent harvest strategy to inform scaup harvest management decisions. Within this framework, the harvest strategy prescribes an optimal harvest level given an observed breeding population size and an explicit harvest management objective. In addition, we analyzed historical harvest data to develop predictive, Flyway-specific harvest models and to calculate a Flyway-specific proportional harvest allocation. The Bayesian assessment resulted in an estimate of maximum sustainable yield (MSY) for scaup of 0.389 million birds. We then used the estimates from the Bayesian assessment to generate optimal harvest strategies with stochastic dynamic programming while considering a large number of different models in the optimization. We derived state-dependent harvest strategies for a set of objective functions that ranged from 100 percent of the maximum long-term cumulative harvest to 90% MSY. Given the current status of the scaup population, contemporary scaup harvest estimates exceed the optimal harvest levels specified under each strategy regardless of the objective function used during the optimization. We then characterized possible regulatory alternatives that would be expected to achieve Flyway-specific target harvest levels in relation to a range of optimal, allowable harvest totals. For the 2007 regulations cycle, we propose that this assessment framework be used to calculate an optimal scaup harvest level under an objective to achieve 95% of MSY. The historical harvest allocation would then be used to determine Flyway-specific, allowable harvest levels, and the harvest modeling results would subsequently be used in developing a set of scaup harvest regulations for consideration during this years regulations cycle.