Segregation edaphique et bathymetrique chez le crabe des neiges,Chionoecetes opilio (0. Fabr.), dans le sud-ouest du golfe du saint-~aurent' Francis ~o u l o m b e ,~ lean-Claude F. BrOthes, Roxane Bouchard et Caston EIesrosiers3 Dgparternene d'Qs&ansgrapAie, Universitg du Quebec d Rirnouski, 300, avenue des Ursulines, Rimouski CQu4.1 C5L 3A 7 Coulombe, F., 8.X. F. BrGthes, R. Bouchard et 6. Desrosiers. 1985. Segregation edaghique et bathym6trique chez le crabe des neiges, Chionoecetes opilio (8. Fabr.), dans le sud-ouest du golfe du Saint-kaurent. Can. 8 . Fish. Aquat. Sci. 42: 169-180. Des observations skar une population de Chionoecetes opilio ont 6te effectuees au csurs des et6 1980 et 1981 dans B e sud-ouest du golfe du Saint-baurent, a Itentr6e de la baie des Chaleurs et de la baie de Gasp6. h%chantillonnage a 6t6 realis6 a I'aide d'un chalut a perche et de casiers appAtes, 5 des profondeurs variant de 45 a 125 m. bes largeurs de carapace des crabes des deux sexes ont kt6 mesur6es et la maturit6 physiologique determinee par indice biometrique. hes individus pr6matures des deux sexes se distribuent preferentiellement aux niveaux bathymbtriques superieurs sur des substrats h6terog&nes gravelovaseux tandis que les adultes sont rencontres surtout en profondeur sur les fonds de vase et de vase sableuse. On 6met Ithypoth&se que les jeunes crabes descendent vers les fonds de vase oh se produit B e recrutement 21 la peche. Ce deplacement serait concomittant I'apparition de la maturit6 physiologique. A population of Chionoecetes opblio was studied during the summers sf 1988 and 1981 in the southwestern Gulf of St. Lawrence, at the entrance of the Bay of Chaleur, and the Gasp6 Bay. Sampling was conducted with beam trawls and baited traps at depths ranging from 45 to 125 m. Crab shell width of both sexes was measured and maturity determined according to a biornetrical index. immature individuals of both sexes are essentially localized on the upper bathymetrical levels, on gravelly mud, whereas aduits are found mainly on mud or sandy mud bottoms. We hypothesize that young crabs move down to the muddy bottom where recruitment to the fishery occurs. This deplacement seems to be concomitant with physiological maturity. Can. J o Fish. A q u~t . Sci., Vol. 42, 1985 169 Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by McMaster University on 11/17/14 For personal use only. 170 Can. 9. Fish. A q~a r . Sci., Val. 42, 1985 Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by McMaster University on 11/17/14 For personal use only. 174 Can. 9. Fish. Aquar. Scb., V01.42, 1985 Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by McMaster University on 11/17/14 For personal use only. 146 Can. J . Fish. Aquar. Sci., V Q~. 42, 1985 Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by McMaster University on 11/17/14 For personal use only. 138 Can. J . Fish. Aquat. Sci., Val. 42, I985 Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by McMaster Univ...

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Time of hatching, abundance of recently-hatched larvae and their relative contribution from the Georges Bank and Nantucket Shoals spawning grounds, as well as mortality during the autumn-winter period are esti mated for eight spawning seasons on the basis of data from the ICNAF Larval Herring Surveys which were conducted during 1971-78. Indices show that the highest initial larval production occurred in 1973 and 1974 as a result of the large 1970 year-class and that there was a decline in production of about two orders of magnitude by 1976 and thereafter. The collapse of the fishery on Georges Bank in 1976 coincided with a deiay in peak spawning from mid-to late-October, a contraction of the spawning season, and a shift of the remaining spawning population to northwestern Georges Bank and Nantucket Shoals. Furthermore, the mean seasonal mortality rate of 5% per day, estimated over the first 6 months of life, varied significantly (3-7%/day) after the 1975 season. The initial larval production estimates are compared with abundance indices (age 3+ herring) from spring bottom-trawl surveys, and sources of bias are evaluated.

Size distributions of the exploited snow crab (Chionoecetes opilio) population in the southwestern Gulf of St. Lawrence were obtained from commercial landings in New Brunswick ports during 1977-82. The unexploited part of the stock was sampled during research vessel surveys in 1980 and 1981. The size distributions were analyzed by factorial analysis of correspondence. The trend in mean size was negative from 1977 to 1981 and positive thereafter. The analysis identified two periods of recruitment to the standing stock within each year: the first at the beginning of summer and the second in late summer and autumn. Growth of the previouslyrecruited crabs occurred between these two periods. Analysis of research vessel data indicated that many prerecruits inhabited areas outside the usual fishing grounds. The hypothesis is proposed of recruitment by platoons, with a part being due possibly to migration of crabs from shallow unexploited areas to deeper water where the commercial fishery occurs.

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