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Evaluating Benchmarks of Biological Status for Data-limited Populations (Conservation Units) of Pacific Salmon, Focusing on Chum Salmon in Southern BC.

author Holt et al.
published year 2018
document type government
species chum
location British Columbia
subjects recruitment, Wild Salmon Policy, benchmarks, data limited, productivity
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Status assessments for Chum Salmon (Oncorhynchus keta) under the Wild Salmon Policy (WSP) have been limited, in part because recruitment time-series required to calculate stockrecruitment based benchmarks are not consistently available. Alternative benchmarks have been proposed for data-limited Conservation Units (CUs) using percentiles of the observed spawner abundance time-series. However, these benchmarks have not been evaluated against stock-recruitment benchmarks currently used to assess status on abundances for data-rich CUs. Our goals were to evaluate percentile-based benchmarks against stock-recruitment based benchmarks accounting for high uncertainties and possible biases in spawner abundances, catches, recruitment estimates, and age-at-maturity. We used two approaches to evaluate benchmarks based on a retrospective comparison through the historical record and a prospective simulation model under numerous hypothetical future scenarios. We demonstrate an approach for providing assessments that accounts for uncertainties in benchmarks, and provide advice on the applicability of percentile-based benchmarks for data-limited CUs of Chum Salmon relative to stock-recruitment benchmarks used for data-rich CUs. In general, our results support the application of percentile-based benchmarks for data-limited CUs of Chum Salmon when productivity is moderate to high (>2.5 recruits/spawner) and harvest rates are low to moderate (≤40%). However, we suggest further evaluation of percentile benchmarks (and the consideration of alternatives) when productivity is expected to be low and/or harvest rates high. Under these conditions, concurrent declines in abundances and percentile benchmarks can results in status assessments that are more optimistic than those from stock-recruitment benchmarks due to a shifting baseline.