Research Document - 2006/031

An assessment of Newfoundland and Labrador snow crab in 2005

By Dawe, E.G., D. Mullowney, D. Stansbury, D.G. Parsons, D.M. Taylor, H.J. Drew, P.J. Veitch, E. Hynick, P.G. O’Keefe, and P.C. Beck

Abstract

Resource status was evaluated, by NAFO Div., based on trends in biomass, recruitment prospects and mortality. Data were derived from the fall Div. 2J3KLNO and the spring Subdiv. 3Ps multispecies bottom trawl surveys, inshore Div. 3KL trap surveys, and fishery data from logbooks as well as at sea 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 survey size frequency distributions. Mortality was inferred from exploitation rate indices, pre recruit mortality indices and prevalence of Bitter Crab Disease (BCD). No fishery independent data were available for Div. 4R. In Div. 2J the exploitable biomass indices increased slightly in 2005 and recruitment is expected to increase in 2006. Fishery induced mortality, on the exploitable as well as the pre recruit populations, has decreased since 2003. Although fishery induced mortality has decreased, the exploitable biomass remains low. Increase in exploitation in 2006 may impair further recovery. In Div. 3K, the exploitable biomass remains low and offshore recruitment is expected to remain unchanged or increase slightly in the short term. The exploitation rate index, as well as pre recruit mortality index, were similar in 2005 to the long term average. Any increase in exploitation in 2006 would further impair recovery. In Div. 3L the fall survey biomass index and the commercial CPUE do not agree. The exploitable biomass index declined from 1996 2000 and remained relatively low thereafter. Offshore CPUE decreased between 2002 and 2004 and changed little to remain at a high level in 2005 relative to other divisions. Inshore CPUE decreased in 2003 and has changed little since. Recruitment is expected to remain relatively low in the short term. The exploitation rate index increased from 1996 to 2000 and has since changed little. The pre recruit mortality index increased gradually to 2001, doubled to 2003, and then decreased to the 2001 level. The effect on exploitation rate of maintaining the current catch level remains unclear because trends in the exploitable biomass index and CPUE do not agree. However, the current level of fishery removals would not likely result in increased mortality on either the exploitable or pre recruit population. In Div. 3NO, estimates of the fall survey exploitable biomass and pre recruit indices have wide margins of error. Therefore, no inferences about trends can be made from these data. Commercial CPUE has remained high in recent years relative to other areas, but decreased by 31% between 2002 and 2005. The percentage of the total catch discarded in the fishery has remained steady during the last 4 years at a low level, implying little wastage of pre recruits. The effects of maintaining the current catch level on fishery induced mortality are unknown. In Subdiv. 3Ps CPUE trends indicate that the exploitable biomass has become depleted but recruitment prospects have improved. Exploitation, in the short term, would likely impair recovery of the exploitable biomass. 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 the percentage of the catch discarded. The effects of maintaining the current catch level on the exploitation rate or pre recruit mortality 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.

Complete document (PDF, 3982 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.