Research Document - 2008/009
An Assessment of Newfoundland and Labrador Snow Crab (Chionoecetes opilio) in 2006
By E. Dawe, D. Mullowney, D. Stansbury, D. Taylor, E. Hynick, P. Veitch, J. Drew, P. O’Keefe, K. Skanes, D. Fiander, R. Stead, D. Maddock Parsons, P. Higdon, T. Paddle, B. Noseworthy, and S. Kelland
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 multispecies bottom trawl surveys, inshore and offshore Div. 3KLPs4R 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 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). The fall multi-species surveys in Div. 2J3KLNO indicate a decline in exploitable biomass since 1998. However both the survey indices and commercial CPUE agree that the exploitable biomass has increased in the north (Div. 2J3K) in 2006 but continued to decline in the south. Recruitment has increased overall in 2006 due to increases in the north, while prospects have improved in the south. Longer-term recruitment prospects are uncertain but the persistence of a warm oceanographic regime implies poor prospects relative to the strong recruitment of the late 1990’s. In Div. 2J the fall survey exploitable biomass index has increased over the past four years but remains low. Commercial CPUE doubled from a record low level in 2004 to about the long-term average in 2006. Recruitment has increased since 2004 and prospects remain promising for 2007. The exploitation rate index has declined since 2003 while the pre-recruit fishing mortality index decreased to a very low level. An increase in exploitation rate in the short term that results in increased pre-recruit mortality could impair further recovery. In Div. 3K, the fall survey exploitable biomass index has increased since 2003 to the long-term average. Both offshore and inshore commercial CPUE increased in 2006 to their long-term averages. Recruitment has increased in 2006 and prospects remain promising for 2007. The exploitation rate index was unchanged from 2005 at about the long-term average whereas the pre-recruit fishing mortality index decreased sharply to its lowest level. Any increase in exploitation rate in the short term that results in increased pre-recruit mortality could impair recovery of the exploitable biomass. In Div. 3L the fall survey exploitable biomass index was at its lowest level in 2006. Offshore commercial CPUE has changed little in the past three years and remains below the long-term average but high relative to other divisions. Inshore CPUE increased in 2006, approaching the long-term average. Recruitment is expected to remain low in the short term. The exploitation rate index has changed little since 2001 while the pre-recruit fishing mortality index was about average. Maintaining the current level of fishery removals, in the short term, will likely result in some increase in the fishery-induced mortality rate. In Div. 3NO, survey indices are unreliable. Commercial CPUE has changed little over the past three years and remains high relative to other areas. Recruitment has been low in recent years and short term prospects are uncertain. The effects of maintaining the current catch level on the fishery-induced mortality rate are unknown. In Subdiv. 3Ps offshore and inshore CPUE increased slightly in 2006 from record low levels in 2005. Recruitment should increase over the next three years. Increased removals, in the short term, would likely impair recovery of the exploitable biomass. In Div. 4R, there are insufficient data to assess resource status. Throughout Div. 2J3KLNO, the percentage of mature females bearing full clutches of viable eggs has remained high since 1995 with no clear trend.
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