1993. Density-dependent geographic distribution of Atlantic cod (Gadus rnorkua) in the southern Gulf of St. Lawrence. Can. j. Fish. Aquat. Sci. 50: 725-733.We tested effects of population sine on the geographic distribution of Atlantic cod (Gadus rnorhud) in the soutl~ern Gulf af St. Lawrence for age gro~rps 3-8 + over the period 1971 -90. Distribution was density dependent far all six age groups. Geographic range or stock area increased with abundance for each age group. Variation in abundance explained 63-94" of the variation in stock area. During periods of low abundance, the highest cod densities occurred in western regions sf the southern Gulf for all age gro~rps. Geographic distribution during these periods was nsore restricted for younger cod than for older cod. Density of age-3 cod was relatively high in only one of three western regions whereas densities of older cod were relatively high in ttzlo or all of these regions. As abundance increased, density increased slowly in the regions where cad were concentrated at low population sizes and more rapidly in surrounding regions. The greatest densities were found in the same area at low and high levels of abundance for younger cod but in different areas at these two abundance levels for older cod. We discuss this variation in geographic distribution in terms of density-dependent habitat selection and note its implications for stock assessment.Nous avans verifie les effets de la taille de la population sur la &partition geographique de la morue de IfAtlantique (Cadus ~norhua) dans le sud du golfe Saint-baurent; nous avons ktudie les groupes d'iges 3-8 + au cours de la periode 1371 -1 990. La distribution dependait de la densite pour les six groupes d'ige. L'aire de repartition des stocks a augmente avec I'abondance pour chacun des groupes d'ige. La variation de I'ahondance explique 63 a 94 % de la variation de I'aire de repartition des stacks. Durant les pkriodes de faible abondance, les plus fortes densites de morues ont 4te sbserv6es dans les regions occidentales du sud du golfe pour tous les groupes d'dge. Au cours de ces periodes, la repartition geographique est plus restreinte dans le cas des jeunes nlorues que dans celui des morues plus 2gees. La densite des morues d'ige 3 etait relativement elevee dans une seule des trois r6gions occidentales, tandis que la densite des morues plus agees etait relativement klevee dans deux ou dans l'ensemble de ces regions. Au fur et 2 mesure que I'abondance a a~rgrnente, la densite a augment6 lentement dans les regions ob la marue etait concentrke lorsque la taille de la population etait faible, et elle a augmente rapidernent dans les regions avoisinantes. Les densites les plus klev6es csnt 6te observees aux rn@mes endroits, que I'abondance ait kt6 faible au elevee, dans le cas des ieunes morues, mais dans des endroits differentes dans celui des marues plus dgees. Nous traitons de cette variation de la repartition geagraphique de la morue en termes de selection de I'habitat iiee a la densite et soulignons les implicatio...
The ideal free distribution (IFD), a hypothesis from behavioural ecology, predicts that fishery effort should map resource distribution better than catch-per-unit-effort (CPUE) when interference competition occurs in the fishery. We tested this prediction using data from the fishery and annual research survey for snow crab (Chionoecetes opilio) in the southern Gulf of St. Lawrence. Effort was positively correlated with the local abundance of crabs in all years. Correlations between CPUE and local crab abundance were also positive in some years, but negative in others. In the latter cases, CPUE and effort were also negatively correlated, suggesting intense competition in the fishery. In most years, CPUE tended to be equalized among areas compared with the distributions of effort and local crab abundance, as predicted by the IFD. In most years, differences in spatial distribution were more significant between CPUE and crab abundance than between effort and crab abundance. Although effort was the more reliable indicator of resource distribution, even it provided a distorted view of this distribution, as predicted given expected violations of IFD assumptions. For example, effort tended to be higher than expected on fishing grounds near home ports and lower than expected on distant grounds.
The effect of temperature on molting frequency and size-at-terminal molt of the snow crab Chionoecetes opilio was investigated and compared between 2 Canadian Atlantic ecosystems based on spring and summer surveys. We found that the size-at-terminal molt was directly related to temperature but that the effect of temperature was much clearer and occurred at smaller sizes for females than for males. By focusing on recently molted (new-shelled) crabs, we showed that size-at-terminal molt is conditioned by temperature over a variable number of instars and intermolt periods leading up to the terminal molt. Crabs of both sexes larger than about 50 mm carapace width (CW), on annual molting schedules, sometimes skipped a molt. The frequency of skip-molting differed between the areas and sexes, and was directly related to size and in versely related to temperature. We develop a hypothesis to explain the relationships of terminal size with temperature and molting frequency that is consistent with life-history theory and snow crab bioenergetics and considers differences between the sexes. The implications to natural mortality and recruitment to fisheries are also discussed.
The life history of the American lobster, Homarus americanus, has been studied in the Bideford River estuary, Malpeque Bay, on the northern shore of Prince Edward Island, Canada. Lobsters migrate into the bay in early summer and two distinct moultings take place in May-June and in September. Lobsters with missing claws moult in both seasons, while uninjured individuals mainly moult in May-June. Neither uninjured lobsters nor individuals with missing claws larger than 43 mm CL moult twice a year in the estuary. A high percentage (30-40%) of individuals has missing claws in summer and the percentage of animals with regenerated small claws increases towards October-November. After the regeneration of missing claws, lobsters appear to emigrate to deeper water outside the bay. The estuarine environment might be used as a moulting and regenerating area for injured animals in spring-fall. Conversely, this environment does not appear to sustain high reproductive activities, because a low prevalence of mature females is observed throughout the year in this environment. These findings reveal the diversity of habitats used by different stages and groups of lobsters, especially the importance of an estuarine environment for moulting of claw regenerating lobsters. Le cycle de vie du homard americain, Homarus americanus, a ete etudie dans l'estuaire de la riviere Bideford, Baie de Malpeque, au nord de l'Ile du Prince Edouard, Canada. Les homards migrent vers la baie au debut de l'ete et deux mues distinctes ont lieu en mai-juin et en septembre. Les homards depourvus de pinces muent aux deux saisons, tandis que les individus intacts muent principalement en mai-juin. Aucun homard intact, comme aucun individu sans pinces, de taille superieure a 43 mm (CL) ne mue deux fois l'an dans l'estuaire. Un pourcentage eleve (30-40%) d'individus ont des pinces manquantes en ete et le pourcentage d'animaux avec des petites pinces regenerees a augmente vers octobre-novembre. Apres la regeneration des pinces, les homards semblent emigrer en eau plus profonde en dehors de la baie. L'environnement estuarien pourrait etre utilise comme une aire de mue et de regeneration pour les animaux blesses entre le printemps et l'automne. En revanche, cet environnement ne semble pas soutenir une activite elevee de reproduction en raison d'une faible prevalence de femelles a maturite tout au long de l'annee. Ces resultats revelent la diversite des habitats utilises par les differents stades et groupes de homards, en particulier l'importance de l'environnement estuarien pour la mue et la regeneration des pinces.
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