Information identified as archived is provided for reference, research or recordkeeping purposes. It is not subject to the Government of Canada Web Standards and has not been altered or updated since it was archived. Please contact us to request a format other than those available.
Cannibalism occurs in snow crab and has been observed both in the wild and in the laboratory, but crabs larger than 60 mm CW are not killed by large male adult snow crabs either in the wild or in laboratory experiments. We tested the hypothesis that cannibalism failed to occur as smaller snow crabs became large enough to resist the force of larger male snow crabs. Chela force and resistance of the cuticle to loading were compared. Chela, merus, and carapace cuticles differed markedly in mechanical properties. The Chela was hard compared to the merus which was the most flexible cuticle. Strength of the cuticle generally increased with size of crab, but decreased markedly at molting and remained low for several months past molting. The mechanical advantage (MA) of the chela was larger in adult than in non-adult snow crabs of similar size. The force of the Chela was calculated from MA and previously documented size and contractile force of the closer muscle. Closing force at the first denticle on the dactyl of large male adult snow crabs was large enough to break the cuticle of non-adult and adult snow crab of any size. Only crabs less than 60 mm CW, however, were vulnerable to forces delivered at the tip of the dactyl of large adult, but not of large non-adult, snow crab. Factors other than strength of the cuticle may explain size-selective cannibalism.©2000 The Crustacean Society
CASTONGUAY, M., C. ROLLET, A. FRÉCHET, P. GAGNON, D. GILBERT, J.-C. BRÊTHES, 1999. Distribution changes of Atlantic cod (Gadus morhua L.) in the northern Gulf of St. Lawrence in relation to an oceanic cooling. ICES J. Mar. Sci., 56: 333-344 .
TRIPPEL, E.A, M.J. MORGAN, A. FRÉCHET, C. ROLLET, A. SINCLAIR, C. ANNAND, D. BEANLANDS, L. BROWN, 1997. Changes in age and length at sexual maturity of northwest Atlantic cod, haddock and pollock stocks, 1972-1995. Can. Tech. Rep. Fish. Aquat. Sci., 2157, 120 p .
In 1993, Fisheries and Oceans Canada formed a Maturity Working Group in the Atlantic Zone to undertake the task of developing long-term trends in age and length at sexual maturity for several principal gadid stocks. This report presents these findings and comments on their potential application to fishery science and related conservation issues. Substantial declines in age and length at sexual maturity have occurred in the majority of Northwest Atlantic gadid stocks since the mid-1980s and in particular since 1990. Generally, more northerly cod stocks matured at older ages and larger body sizes than southern stocks, though in recent years these differences have narrowed. Within a stock, females generally matured at older ages and larger body sizes than males. Research recommendations are made to support new initiatives that would assist in maintaining the maturity time series for these fish stocks.
FRÉCHET, A., Y. GAGNON, P. SCHWAB, D. D'AMOURS, J.-D. DUTIL, Y. LAMBERT, L. BOURASSA, C. ROLLET, 1994. Revue de l'état du stock de morue du nord du golfe du Saint-Laurent (3Pn, 4RS) en 1993 ; Review of the status of the northern Gulf of St. Lawrence cod stock (3Pn, 4RS) in 1993. MPO, Pêches de l'Atlantique, Document de recherche ; DFO, Atlantic Fisheries, Research document, 94/29, 50 p .
The 1993 fishing season was conducted with many problems. The fishing season started late because of problems linked with enforcement, the fisheries were stopped many times because of small fish. The initial TAC for 1993 of 31,000 t was reduced at the end of August to 18,000 t on the recommendation of the FRCC. This TAC was based on results of last year's assessment and corresponds to a fishery at the F0.1 reference level. Landings for 1993 were of 18,171 t. There are no directed nor sport fisheries on the 3Pn, 4Rs cod stock in 1994. All available indices indicate a large decline in the last year. The mobile gear catch rates drop by 37 % between 1992 and 1993. The population estimates derived from the 1994 January groundfish research vessel survey represent only 51 % of those estimated in 1993. The population estimates from the summer groundfish survey dropped by 65 %. Catch rates from the Index Fishermen declined in certain cases and maintained themselves in others. For the first time, a calibration of SPA was attempted incorporating results from both the summer and winter surveys. The summer survey series is now long enough to be of interest (4 years) and the winter series will be discontinued in 1995. The 3+ population numbers would have gone from 546 million individuals in 1980 to as low as 95 million individuals in 1993 and the biomass of mature fish (7+) in 1993 could be as low as 10,000 t. Because of problems linked with the quality of the research vessel survey information, the calibration with ADAPT produces anomalously high fishing mortalities. The analysis is thus presented for illustrative purposes only and no projections were done. Biomass is expected to be very low.
- Date modified: