Research Document - 2004/024
An Assessment of Newfoundland and Labrador Snow Crab in 2003
By
Dawe, E.G., D. Orr, D.G. Parsons, D. Stansbury, D.M. Taylor, H.J. Drew, P.J. Veitch, P.G. O’Keefe, E. Seward, D. Ings, A. Pardy, K. Skanes, P.C. Beck
Abstract
Resource status was evaluated, by NAFO Division, based on trends in biomass, recruitment prospects and mortality. Data were derived from the fall Div. 2J3KLNO multi-species bottom trawl survey, an inshore Div. 3K trap survey, and fishery data from logbooks as well as observer data. The fall multispecies survey is conducted near the end of the fishing season and so is considered to provide an index of the exploitable biomass that will be available to the fishery in the following year. Trends in biomass within Div. 2J3KLNO were inferred based on comparison of trends in the fall survey exploitable biomass indices with offshore fishery catch per unit effort (CPUE) trends. Short-term recruitment prospects were inferred from comparison of fall survey pre-recruit indices with an observer-based index of crabs discarded in the fishery. Long-term recruitment trends were based on annual progression of male size groups through standardized fall survey size frequency distributions. Mortality was inferred from exploitation rate indices, a fishery observer-based index of handling mortality and prevalence of Bitter Crab Disease (BCD). No fishery-independent data were available for Subdiv. 3Ps or Div. 4R. In Div. 2J trends in both the fall survey index and fishery CPUE indicate that the biomass has declined steadily since 1998. Both short-term and long-term recruitment prospects are uncertain and the exploitation rate as well as pre-recruit mortality will likely increase in 2004 if the current catch level is maintained. In Div. 3K, trends in both the fall survey indices and offshore CPUE indicate that the biomass has recently stabilized at a lower level relative to 1998. Inshore trap survey data suggest some recent increases inshore. Survey and fishery indices agree that recruitment is expected to remain relatively low in the short term, whereas long-term prospects are uncertain. The Div. 3K exploitation rate will remain relatively high if the current catch level is maintained but would not likely increase. In Div. 3L the trawl survey and the commercial CPUE biomass indices do not agree. Whereas the survey data suggest a decline since 1996, the fishery continues to perform at a high level. Recruitment is expected to remain relatively low in the short term, whereas long-term prospects are uncertain. The effect on the Div. 3L exploitation rate of maintaining the current catch level is unknown, because trends in biomass indices do not agree. In Div. 3NO trends in the exploitable biomass index are unclear, but the fishery continues to perform at a high level. In Subdiv. 3Ps CPUE has declined in recent years and recruitment is expected to change little in the short term. Assuming that CPUE reflects the exploitable biomass, and the declining trend continues, exploitation rate and pre-recruit mortality will likely increase if the current catch level is maintained. In Div. 4R CPUE has remained relatively stable in recent years and recruitment is expected to change little in the short term. Assuming that CPUE reflects the exploitable biomass, and remains stable in 2004, the Div. 4R exploitation rate will likely remain unchanged if the current catch level is maintained. There was a slight decline in the percentage of mature females bearing full clutches of viable eggs in Div. 2J3LN since 1995, but the significance of this trend and implications for future recruitment are unknown. Spatial and temporal trends in the prevalence of BCD are unclear and implications for mortality are unknown.
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