Research Document - 2010/113
Assessment of the LFA 41 Offshore Jonah Crab (Cancer borealis) (NAFO 4X and 5Zc)
By D.S. Pezzack, C.M. Frail, A. Reeves, and M.J. Tremblay
Abstract
The offshore Jonah crab fishery began in 1995 when a 720t Total Allowable Catch (TAC) was established for the Lobster Fishing Area (LFA) 41 lobster fishery. The species is fished as a by-catch in the lobster fishery and by vessels targeting the crab. The offshore lobster fishery (LFA 41), established in 1972, fishes from the 50 nautical mile line (92 km) out to the upper continental slope. While LFA 41 includes parts of NAFO areas 4Vs, 4W, 4X and 5Z, historically fishing only occurs in 4X and 5Zc.
The status of the Jonah crab stocks in LFA 41 was last assessed in 2000, and the Jonah crab fishery presently operates under the 2006-2010 Integrated Harvesting Plan as a male only fishery with a minimum size of 130mm Carapace Width (CW) fished by 8 licences and a TAC of 720t. Since the 1960s, Jonah crab stocks have been exploited as a trap by-catch to inshore and offshore lobster fisheries. Accurate landings are not available from these early fisheries. In the early 1980s, an experimental Jonah crab fishery concentrating in LaHave and Emerald basins on the Scotian Shelf lasted only two years, before poor economic conditions resulted in the fishery closure.
The development of the LFA 41 Jonah crab by-catch fishery in 1995 resulted in more widespread fishing activity within the traditional offshore area as vessels fished further east where crab concentrations were present. An experimental Jonah crab fishery took place in 4W between 1999 and 2002. Inshore Jonah crab fisheries also developed in LFAs 33 and 34. After initial high landings these fisheries have declined since 2000 with little or no activity in 2007 or 2008.
The 720t Jonah crab TAC was obtained or nearly obtained between the 1996-1997 and 2000-2001 seasons. Landings then declined sharply with 14t landed in 2007. At present there is no directed fishery.
The abundance indicators (standardized and non-standardized Catch Per Unit Effort (CPUE)), suggest that Jonah crab abundance in LFA 41 has declined since the fishery began in 1995. Adjusted mean stratified number per tow in the DFO Research Vessel (RV) bottom trawl surveys also show a general declining trend in all the strata fished in LFA 41. This is in contrast to the lack of a declining trend in areas adjacent to LFA 41. The decline is sharpest in the 1999-2002 period in the strata corresponding to Crowell Basin and Georges Basin. The time series of the trawl surveys is short (1999-present) and issues of catchability, trawlable bottom and the variance around the mean values needs to be further evaluated.
The time series of at-sea samples and DFO RV surveys are too short to evaluate production or recruitment trends for Jonah crab in LFA 41
The causes of the decline in Jonah crab abundance indicators cannot be given with certainty, but it appears that low (relative to most fisheries) fishing pressure has contributed to a substantial reduction in the biomass that was present at the start of the fishery and the TAC of 720t set in 1995 does not appear to have been sustainable. Future Jonah crab fisheries will have to rely on annual recruitment and growth. Females are not allowed to be retained regardless of size and, therefore, the potential reproductive capacity of females is protected as long as there are sufficient males available and discards are low. At present there is no directed fishery, and the abundance indices from the DFO RV survey will be used to follow the recovery. Other information sources may also be examined, including by-catch recorded in the offshore lobster fishery and water temperature over the shelf.
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