Research Document - 2002/14
Assessment of the western Cape Breton snow crab fisheries (Areas 18 and 19) within the southeastern Gulf of St. Lawrence unit in 2001
By M. Hébert, E. Wade, and M. Moriyasu
Abstract
The assessment of the western Cape Breton snow crab fisheries, Areas 18 and 19, was done based on information collected from fishermen's logbooks, at-sea and port samplings, and post-season trawl survey.
In Area 18, a quota of 476 t was allowed despite of a very low biomass index, which resulted in the lean total landings slightly exceeding 50% of the quota. All available stock indices indicated a negative condition of immediately exploitable stock. The mean CPUE for the 2001 season was at the lowest level since 1985 (15.3 kg/trap haul). The mean size of commercially caught crab has been decreasing since 1995. However, the 2001 trawl survey results showed that the biomass/abundance indices of adult legal-sized males projected for 2002 and future recruitment slightly increased despite of very large confidence intervals. We attribute this increasing trend in biomass to the relative high abundance of large instars within the Area since 1999. The larger-sized adolescent groups started to appear in the catch in the 2001 season as soft/white crabs. The relative abundance of pre-recruits (R-2, R-3) was at the highest level since 1993. Therefore, there is a good potential for the growth in abundance of commercially exploitable crab in the near future (2-4 years), although this depends largely on the extent of fishing effort put in the adjacent fishing Areas (Areas 12 and 19) and also the seasonal movement of crab in and out of the area. This high abundance of pre-recruits may result in a high incidence of soft-shell/white crabs. For 2002, it is strongly recommended to follow the soft-shelled crabs protocol in order to protect the future recruitment to the fishery.
In Area 19, a quota of 3,912 t, the highest quota ever allocated in the history of this fishery, was caught. The fishery performance reacted positively resulting in a 28 % increase in CPUE (88.5 kg/trap haul) compared to the 2000 season. However, this level was lower than that observed in 1999 (the highest CPUE for the Area). The percentage of soft-shelled crab was below the mean over the last 5-yrs, but showed a slight increase since 1999. The mean size of commercially caught crab has been decreasing since 1996. The commercial biomass index projected for 2002 (5,214 t) decreased by 20% (although with a wider confidence limits) from the 2001 season. This may be due to a net decrease of recruitment to the fishery (2,927 t, representing 56% of the commercial biomass index) compared to the 2001 season (i.e., 4,614 t, representing 68% of the commercial biomass index). The relative abundance of pre-recruits (R-2, R-3) was at its highest level ever recorded since the beginning of the survey (1990). This high abundance of pre-recruit may result in a high incidence of soft-shell/white crabs during next couple of years. For 2002, it is, therefore, strongly recommended to follow the soft-shelled crab protocol in order to protect the future recruitment to the fishery.
Geographic distribution of females, adolescents, and adult males in the southern Gulf of St. Lawrence showed that the snow crab population is continuously distributed in all fishing areas. There was a tendency of movement of larger instars towards southeastern Gulf. In the southern Gulf of St. Lawrence, the abundance of multiparous females has been decreasing from 1990 and reached the lowest level in 1995 and peaked again in 1997-98. Currently, the primiparous females abundance is decreasing. In the southeastern unit, the same fluctuation pattern of primiparous and multiparous females is observed. The difference between the two sub-units is that the abundance of preprimiparous females is still high in the southeastern unit. However, there is no sign of immediate decline in the population's reproductive potential in both sub-units. An increasing population of primature (preprimiparous) and new mature (primipares) females suggested a necessity to protect (i.e. lower exploitation) the most reproductive group of adult males (carapace categories 3 and 4) to ensure a high stock reproductive potential.
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