Missing the target: uncertainties in achieving management goals in fisheries on Fraser River, British Columbia, sockeye salmon (Oncorhynchus nerka)

Abstract

In sockeye salmon (Oncorhynchus nerka) fisheries, management targets are rarely achieved exactly, thereby creating uncertainties about outcomes from implementing fishing regulations. Although this type of uncertainty may be large, it is seldom incorporated into simulation models that evaluate management options. One objective of this study was to quantify the deviations that occur between realized and target mortality rates (i.e., the target fraction of adult recruits that die each year during return migration, mostly due to harvesting) in fisheries for sockeye salmon from the Fraser River, British Columbia. We found that for some sockeye stocks, realized mortality rates were higher than targets when recruitment was low (resulting in conservation concerns) and lower than targets when recruitment was high (resulting in foregone catch). Scientists and managers can at least partially account for effects of such deviations between realized and target mortality rates (outcome uncertainties) by choosing target harvest rules that reflect typical patterns in those deviations. We derived a method to permit modelers to incorporate those patterns into analyses of management options.

Consideration of uncertainties in environmental science and management with examples from Pacific salmon

“…Deviations from targets may be state dependent and biased. For instance, Holt and Peterman (2006) found that at low salmon abundance, percentage mortality rates were higher than the target more often than below it (Fig. 2).…”

“…Such management-derived errors are generally referred to as implementation errors. The general term "outcome uncertainty" encompasses all three causes described above (Holt and Peterman, 2006). Similar to natural variability and observation error, outcome uncertainty can be represented by a variance term in models.…”

“…Thus, even this simple change in how scientists present results about probabilities could enhance their communication with decision makers and the public. Anderson (1998Anderson ( , 2001 Holt and Peterman (2006).…”

Distinguishing benchmarks of biological status from management reference points: A case study on Pacific salmon in Canada

“…However, it is widely recognized that regulatory control is imperfect because of lack of enforcement and/or the relationships between harvest control measures and desired outcomes are not well understood (Dichmont et al 2006;Fulton et al 2011). Furthermore, decision-makers may deliberately deviate from agreed upon reference points in response to immediate social or political pressures when faced with difficult options, such as closing a fishery (Dichmont et al 2006;Holt & Peterman 2006;Fulton et al 2011).…”

Retrospective bioeconomic analysis of Fraser River sockeye salmon fishery management

“…Note that we include no stochastic elements in our simulations, e.g., in the implementation of harvest strategies, which can sometimes be problematic (Holt and Peterman, 2006). We recognize that this deterministic approach glosses over some potentially important implementation difficulties.…”