Research Document - 2004/132
Development of a New Fishery for Tanner Crabs (Chionoecetes tanneri Rathbun, 1893) off British Columbia: 2003 Status Report
By Gillespie, G.E., K.H. Fong, A.C. Phillips, G.R. Meyer, J.A. Boutillier
Abstract
This paper presents new information gathered since the previous report on offshore Tanner crab (Chionoecetes tanneri) fishery development in 2000. Results of DFO trap and trawl surveys, Industry trap surveys, landings from an experimental trap fishery and bycatch from groundfish trap and trawl fisheries were used to examine distribution of Tanner crabs off the coast of British Columbia (B.C.) and identify areas with potential to support a commercial fishery. Abundance increased from the B.C.-Washington border to peak abundance off central and northern Vancouver Island, then decreased off the mouth of Queen Charlotte Sound and off the Queen Charlotte Islands.
Landings and observer data from the experimental fishery were used to examine impacts of a directed trap fishery on Tanner crabs and other species caught incidentally. Bycatch rates were relatively low and the primary bycatch species were scarlet king crabs (Lithodes couesi) and sablefish (Anoplopoma fimbria). Concern was noted at the relatively high catch rates of female and undersize male Tanner crabs.
Landings from the experimental fishery and other offshore fisheries were used to describe impacts of these fisheries on the Tanner crab resource. Bycatch of Tanner crabs from the groundfish trawl fishery increased from 30 t in 1996 to 133 t in 2002. Limited data from observer trips and DFO trap surveys suggest that Tanner crabs are regularly encountered in the sablefish trap fishery.
New information was used to critically examine the existing assessment framework and verify biological assumptions used to date. Preliminary biomass estimates were calculated from catch rates in the Industry trap survey and swept-area abundance estimates from DFO trawl surveys. A proposed depletion experiment was not successful as fishers moved gear when catch rates dropped to an economic threshold which led to unrealistic stability in catch-per-unit-effort.
Bitter crab disease, infection of crabs by the parasitic dinoflagellate Hematodinium sp., may play a role in determining year-class strength in Tanner crabs. Prevalence ranged from 1-13% of Tanner crabs examined in a limited number of tows during DFO trawl surveys.
Recommendations included initiation of annual assessments using trawl gear in the experimental fishery area and an unharvested control area; restriction of fishery development to the west coast of Vancouver Island; continuation of an experimental fishery to examine productivity from a limited area of the coast; development of an ecosystem-based management framework for fisheries on the continental slope; examination of the feasibility of tagging studies for Tanner crabs; effort standardization studies to examine the relationship between soak time and catch rate; evaluation of gear modifications to exclude females and undersize males in the trap fishery; and completion of the trawl survey off the Queen Charlotte Islands.
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