Research Document - 2005/013
An Assessment of Newfoundland and Labrador Snow Crab in 2004
By Dawe, E.G., D.M. Taylor, D. Stansbury, H.J. Drew, A. Pardy, P.J. Veitch, E. Hynick, P.G. O’Keefe, P.C. Beck, D. Mullowney, and K. Skanes
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, inshore Div. 3KL trap surveys, 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 fall survey size frequency distributions. Mortality was inferred from exploitation rate indices, observer based indices 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 the exploitable biomass remains low but recruitment appears promising in the short term. The exploitation rate as well as pre-recruit handling mortality remained relatively high in 2004. Continued exploitation, in the short term, would likely impose a very high mortality on immediate pre-recruits that would seriously impair recovery of the exploitable biomass. In Div. 3K, the exploitable biomass remains low and offshore recruitment is expected to remain unchanged in the short term. The exploitation rate as well as pre-recruit handling mortality remained relatively high in 2004. Fishery-induced mortality is expected to remain high in 2005 if the recent catch level is maintained and current fishing practices persist. In Div. 3L the fall survey biomass index and the commercial CPUE do not agree. The survey data suggest a decrease since 1996, while the fishery continues to perform at a high level. Recruitment is expected to remain relatively low in the short term, while the exploitation rate index remains relatively high. The percent discarded in the fishery has declined since 1998, suggesting reduced handling mortality on pre-recruits. The effect on exploitation rate of maintaining the current catch level is unknown, because trends in the biomass indices do not agree. In Div. 3NO trends in the fall survey exploitable biomass index and pre-recruit index cannot be interpreted because of wide margins of error. However, the fishery continues to perform at a high level but observer data suggest that recruitment will remain relatively low in the short term. The effects of maintaining the current catch level on the exploitation rate are unknown but handling mortality on pre-recruits remains relatively low. In SubDiv. 3Ps both inshore and offshore CPUE have declined substantially 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 remain high if the current catch level is maintained. In Div. 4R, it is not possible to infer trends in exploitable biomass from commercial CPUE data because of recent changes in the spatial distribution of fishing effort. The observer data for this area are insufficient to estimate a reliable pre-recruit index or infer levels of handling mortality. The effects of maintaining the current catch level on the exploitation rate are unknown. The percentage of mature females bearing full clutches of viable eggs has remained high with no clear trend throughout Div. 2J3KLNO since 1995. Spatial and temporal trends in the prevalence of BCD are unclear and implications for mortality are unknown.
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