Research Document - 2003/046

Halibut on the Scotian Shelf and Southern Grand Banks - Current Estimates of Population Status

By Zwanenburg, K., Wilson, S., Branton, R., and Brien, P.

Abstract

• FRCC recommended increases in TAC in 2000 and 2001, resulting in a current 2002 TAC of 1150t.
• White hake, cusk, cod, dogfish, and a range of other species, are caught in association with halibut. This has management implications in an ecosystem context. In the Industry-DFO halibut longline survey, the average non-halibut by-catch (% weight of all species) has ranged from 76 to 88% in the fixed station phase to between 46 and 69% in the commercial index stations. The latter would be more indicative of bycatch rates in the fishery as a whole.
• According to industry, there has been an increase in the amount of unreported halibut catch, particularly in 2002.
• Adult halibut have a low catchability to the DFO summer RV survey, resulting in highly variable estimates of adult abundance. The RV survey provides information on incoming recruitment (fish < 81cm) and overall spatial distribution. The RV survey shows below average recruitment in 2002; and has been relatively stable over the past decade.
• The halibut longline survey provides the capacity to monitor the halibut population. It has now been in place for five years, is internally consistent (rankings of high, medium and low strata are consistent, fishing grounds are consistently identified, and the commercial and fixed station indices give similar trajectories), and does not suffer from the high variability observed in the RV survey series.
• The halibut longline survey indicates lower recruitment numbers in 2002 for the stock area as a whole. Recruitment estimates for SA3 are relatively high in 2001 and 2002 which suggests that SA3 may be a more important recruitment area than previously thought. However; survey coverage in SA3, particularly 3NO, remains problematic mainly due to the costs involved in getting there and management restrictions related to cod bycatch limits.
• Halibut longline survey commercial index and fixed station estimates of biomass (cpue) show a relatively stable overall population size from 1998 - 2002. Individually, the sub-components of the main survey areas (3Ps4VWX) also appear stable over this period.
• The halibut population biomass appears to be relatively stable even with a 35% increase in TAC and landings since 1998.
• The continued operation of the longline survey to effectively monitor population status, is essential to the management of this fishery.

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