Retrospective Projection Using Monte Carlo Simulation: An Application of a Length-Based Model to Kachemak Bay Pink Shrimp

Retrospective Projection Using Monte Carlo Simulation: An Application of a Length-Based Model to Kachemak Bay Pink Shrimp

Caihong Fu, Terrance J. Quinn II, and Milo D. Adkison

Retrospective Projection Using Monte Carlo Simulation: An Application of a Length-Based Model to Kachemak Bay Pink ShrimpThis is part of Ecosystem Approaches for Fisheries Management
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Description

Pink shrimp (Pandalis borealis), the formerly abundant and commercially important species in Kachemak Bay, Alaska, has declined in population abundance since the mid-1980s. No sign of population recovery has been detected in recent years. This paper is a retrospective look at what the risk to a population would have been under various levels of harvest rate, incorporating uncertainty in natural mortality and recruitment. A lengthbased population dynamics model (Quinn et al., In press) was employed and Monte Carlo simulation was conducted to estimate the probabilities that various harvest strategies would have caused the shrimp population to fall below a threshold. Our results indicated that natural mortality was the most important factor controlling population dynamics, and the increasing trend in natural mortality in the 1980s resulted in the population crash. Because the pink shrimp population had a very high background
risk of extinction, all harvest strategies led to a similar population decline. More effort should be expended in studying the relationship between pink shrimp and its predators. The common assumption of constant natural mortality in stock assessment and population projection should be revisited for forage species like pink shrimp.

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