The Estuaries of Hudson Bay A Case Study of the Physical and Biological Characteristic of Selected Sites

Hudson Bay, which drains 47% of the Canadian land mass, is ringed by estuaries, which form wherever the numerous large and small rivers empty into the bay. General estuarine processes are illustrated by descriptions of five sites encompassing the range of estuarine environments: 1) the Nelson estuary, a well-mixed estuary of the southwestern lowlands; 2) the stratified Churchill estuary, also in the southwestern lowlands; 3) the La Grande estuary, a stratified estuary of eastern James Bay; 4) the partially mixed Eastmain estuary, also of eastern James Bay; and 5) Chesterfield Inlet, a partially mixed estuary within the northwestern tundra. The first four estuaries have been affected by hydroelectric development involving either an increase (Nelson and La Grande) or a decrease (Churchill and Eastmain) in flow. The estuaries and adjacent waters of Hudson Bay generally are nutrient poor and primary production based on phytoplankton appears to be relatively low. Organic debris appears to be an important basis for the estuarine food web. Densities of benthic animals generally increase from fresh to brackish waters. The location of peak benthic densities is variable and appears dependent on local conditions (e.g., variations in substrate, water flow). Estuaries are important to many species of fish which move from the rivers into these areas to feed. Anadromous lake cisco and lake whitefish are often the most abundant freshwater species in the estuaries. Marine species, such as capelin and sand lance, also frequent the estuaries but less is known about their distribution. Beluga whales occur in several of the estuaries during the summer; largest numbers occur in the Nelson estuary. The extensive studies conducted before and after hydroelectric development in the La Grande and Eastmain estuaries have not detected a change in the populations of anadromous lake cisco and lake whitefish, suggesting that neither flow decrease nor augmentation has affected these fish. By inference, the physical changes caused by hydroelectric development did not alter the food webs upon which these fish depend to the extent that the fish populations were affected. This conclusion is supported by studies of other portions of the food web in these areas.