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Mussel colonization is assumed to result from factors affecting recruitment and post-recruitment survival. Despite evidence of passive migration and habitat engineering by adult mussels, the contribution to population dynamics of these processes remains unknown. This research attempts to elucidate the relative importance and scale of (1) adult movement vs. recruitment and (2) of local habitat engineering vs. habitat heterogeneity, for colonization by the blue mussel, Mytilus spp., in the St. Lawrence Estuary, Quebec. Transplants of marked mussels were used to test these ideas. Our results support the hypothesis that colonization mostly occurs through disturbance-mediated adult movement. The scale of this displacement was quantified. Colonization was accelerated by topographic heterogeneity and engineered habitat propagation. These results counter the notion that mussel population dynamics are solely regulated by recruitment and growth, and suggest that distribution patterns are also upheld by adult aggregation and movement from the local scale to landscape level.

Recently, the assumption that marine populations are demographically open due to long-distance larval dispersal has increasingly been challenged. Here we present a large-scale, multi-year survey of blue mussel ( Mytilus spp.) abundance and recruitment along the Southern shore of the St. Lawrence Estuary, Quebec. Using spatial statistical tools we detected significant positive cross-covariance between upstream adults and downstream recruitment at a 14-35 km scale. Adult abundances in subsequent surveys proved to be best explained by past patterns of recruitment, rather than growth indices, or the local supply of recruits. Fucus spp., large macroalgae with much shorter planktonic periods, displayed no evidence of dynamic coupling. Recruitment was instead correlated with growth rate, indicating that local conditions may drive rates of reproduction by Fucus spp. plants. These results provide the first direct quantification of spatio-temporal demographic coupling between adult production and recruitment using survey data, with consequences for metapopulation and marine reserve design.

A prevalence of 76% and a mean intensity of 42.7 Anisakis simplex was found in harbour porpoises (Phocoena phocoena) (N = 78) by-caught in cod gill nets set by fishers from the Gaspe area in summer 1993. No young-of-the-year porpoises (N = 12) were infected. Prevalence and mean intensity among immature and adult porpoises as well as between sexes and length-classes were not significantly different. Anisakis simplex was present in the three stomach compartments of harbour porpoises. Adult stages were proportionately less abundant in the main and pyloric stomachs than the forestomach. Percent intensity of A. simplex was influenced by maturity of harbour porpoises. Gravid female A. simplex contained up to 818,000 eggs. Egg number was highly correlated with worm uttering volume. Density effects were not demonstrated, possibly due to high variability of egg number, total length, uterine and total worm volume between parasites from each stomach and between stomachs of harbour porpoise.

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No description available.

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No description available.

The objective of this study was to understand the pattern of variation in group structure and feeding behaviour of wintering Common Goldeneyes ( Bucephala clangula) on the Saint-Lawrence River, by comparing two major habitats for this species in the province of Quebec, one in freshwater and one in saltwater. Groups of goldeneyes were smaller in Montreal than in the estuary and consisted of twice as many males. Individuals spent a greater proportion of time feeding in Montreal than in the estuary. At Montreal, goldeneyes spent more time feeding under water. Temporal variables had a major influence on group structure and on diving time. At Montreal, time of day explained most of variation whereas in the estuary, tide was more important.

In the marine environment, export production leading to the traditional food chain is a relatively rare event taking place primarily in hydrographic features such as frontal areas. When export production persists, massive reproduction of herbivores is expected to occur. Since copepod eggs and nauplii are the main prey of a majority of fish postlarvae, the spawning of dominant fish species is expected to be associated with fronts. The aims of this study were to determine the influence of an estuarine plume front upon the phytoplankton dynamics (distribution and physiological status) and to assess the role of the cross-frontal circulation upon the distribution of fish larvae and their prey. The frontal area under study is located in the northwestern part of the Gulf of St. Lawrence, at the interface between a coastal jet (Gaspe Current) flowing along the Gaspe Peninsula and the Anticosti Gyre. In early June, maximum phytoplankton concentrations (up to 35 μg chl a L⁻¹) were found in the Gaspe Current. In the salinity gradient, a significant correlation was found between salinity and phytoplankton concentrations (and seston in general), indicating that physical processes (vertical and horizontal mixing) were more important in controlling the seston distribution than biological processes. The dominance of physical processes is probably due to the high current velocities and shear stress in the Gaspe Current in early June. Later during the season, the cross-frontal mixing was less vigorous due to the lower freshwater runoff, and the front acted as a retention zone for estuarine plankton. Maximum diatom concentrations (up to 50 μg chl a L⁻¹) were measured in the front per se. Measurements of nitrogen and silicate concentrations (ambient and intracellular) and uptake rates suggested that silicate generally limited diatom growth across the front. In June, estuarine larvae (capelin, Mallotus villosus and sand lance, Ammodytes hexapterus) were concentrated in the diatom-rich Gaspe Current and front where immature copepod stages were abundant. The five-fold increase in immature copepod concentrations between the gyre and the current/front resulted probably from a food-induced increase in copepod reproduction. Thus it appears that the dispersion strategy of the estuarine species in relation with local hydrography favours the exploitation of the resource-rich Gaspe current and front by the first-feeding postlarvae. The extrusion of redfish (Sebastes spp.) larvae appears to be synchronized with the copepod reproduction that followed the gyre April/May bloom. Later, redfish larvae were also found in abundance in the resource-rich front. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate