Research Document - 2002/127

Biological decision rules for the assessment and management of directed fisheries on Pandalus hypsinotus, Humpback Shrimp.

By Dunham, J.S., Boutillier, J.A., Rutherford, D., and Fong, K

Abstract

This paper examines options for assessing and managing recruitment overfishing in existing and new commercial humpback shrimp fisheries in BC. The biological parameters used in this review are based on a study of a humpback shrimp population in Drury Inlet that was surveyed by Shellfish StAD in November 2001 and March 2002 with trawl and trap fishing gear. In addition, bycatch issues associated with habitat and different gear types used in targeted fisheries are examined.

Aspects of humpback shrimp biology important in this review include estimates of age structure, sexual condition, fecundity, and natural mortality. The humpback shrimp population was composed of 3 age classes, approximately 32% of the shrimp being female. Mean fecundity was 880 eggs per female; however, larger, older female shrimp typically produced a greater number of eggs. Humpback shrimp experienced high natural mortality (mean M=2.0).

Significant variations in population structure estimates were observed depending on the type of fishing gear used. In general, trawl catches of humpback shrimp were more representative of the population, in terms of age and sexual condition, compared to trap catches, which were biased towards larger, older female shrimp. Trends in trap CPUE were more obvious when measuring numbers-at-age rather than weight of shrimp.

Using the information from the Drury Inlet pilot study, three options for assessing and managing recruitment overfishing in directed commercial humpback shrimp fisheries are discussed. These options include: 1) a fixed harvest rate model based on fishery independent shrimp biomass information, 2) a fixed harvest rate model based on fishery dependent CPUE information, and 3) a fixed escapement model based on egg production information.

It was concluded that the management option using a fixed harvest rate with fishery independent assessment procedures is appropriate for both trawl and trap fisheries. In contrast, options using a fixed harvest rate with fishery dependent biomass indices and fixed escapement are only appropriate for a trap fishery. Recommendations on the conservative decision rules associated with these management options are discussed, as well as variations in bycatch in the two fishing options. Recommendations were made on a process for determining humpback shrimp fishing areas where these assessment and management options should be implemented.

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