The Gulf of St. Lawrence Is closed to commercial navigation for nearly five months each year due to ice conditions. In order to lengthen the shipping season, greater knowledge of the behaviour of the ice is necessary. A step in this direction was the inauguration in 1940 of aerial ice surveys in the gulf during the breakup season. The surveys have continued annually for the past thirteen years. Based primarily on the data provided by these surveys, maps were drawn showing the limits of the main ice areas in each breakup season. Although the maps enabled the isolation of several distinct patterns and rates of breakup, they revealed that the behaviour of the ice was extremely variable. The factors influencing ice conditions, including tides, ocean currents, temperature, and wind, were examined with the aim of discovering the causes of the breakup patterns. A number of factors were found to be important in determining the fundamental behaviour of the ice, bat the meteorological factors of temperature and wind appeared to be the chief agents in causing the variable behaviour from year to year. In spite of these variations, it was possible to trace average conditions throughout the Ice season. The chief characteristics of the ice season may be stated briefly. The Gulf of St. Lawrence is never completely covered with ice, but rather, it is partly covered with fields of shifting pack ice between which lie broad stretches of open water. The southern part of the gulf is an area of accumulation where ice conditions are most serious. The clearing of ice from the gulf begins slowly in January and February and becomes accelerated in March and April. The bulk of the ice moves through Cabot Strait to the open Atlantic rather than remaining inside the gulf until it melts. Generally, the ice either withdraws from west to east, passing through Cabot Strait directly, or it stagnates in the southern part of the gulf toward the end of the season. By the first of May the gulf is usually clear of ice which constitutes a hinderance to navigation. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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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.

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Surface water and sediments from the St. Lawrence River system (Quebec region) were analysed for genotoxicity using nonlinear SOS Chromotest parameters, as well as for their chemical concentrations of polycyclic aromatic hydrocarbons and heavy metals. Additionally, sediments chlorobenzenes, polychlorinated biphenyls, organochlorinated pesticides, ammonia and nitrites concentrations were determined. Organic contaminants were extracted dichloromethane. For surface water, fifteen extracts of filtered water and seven of particulates, and for sediments, one extract of pore water and three of particulates proved to be weakly genotoxic. All but one of the genotoxic responses observed in the surface water were obtained from samples taken from the highly industrial portion of the St. Lawrence River system, with the strongest responses observed in Lake St-Louis. Surface water genotoxicants partitioning favors the particulate fraction. Bottom particulates genotoxicity was one thousand fold weaker than suspended particulates. Additionally, whole sediments were extracted with a 10% dimethylsulfoxide-saline solution. Genotoxicity of hydrophilic contaminants was detected in all extracts. The observed distributions of genotoxicity values did not correlate with observed concentrations of demonstrated SOS inducers, mutagens and/or carcinogens, nor with the presence of other toxic chemicals.

Freshwater ecosystems worldwide are being altered by multiple stressors. One of the most important stressors is biological invasion---the introduction of exotic species, which can contribute to the loss of native species. The effects of an introduced species are correlated with its abundance and typically vary across ecosystems, suggesting that its impact on native species is mediated by its environment, i.e. the physical habitat and the recipient community. However, there are few studies that explore the effects of environment on the interactions between exotic and native species. My thesis examines the influence of physical habitat variables and community interactions on the relative abundance of exotic and native freshwater crustaceans in the St. Lawrence River. / The Eurasian amphipod Echinogammarus ischnus invaded the Great Lakes-St. Lawrence River system in the mid-1990s and has replaced the native North American Gammarus fasciatus as the dominant amphipod in littoral areas throughout Lake Erie and Lake Ontario.

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No description available.