Since original construction of the Windsor Causeway across the Avon Estuary in 1970-1,a salt marsh-mudflat system has accumulated on its seaward side. The mudflat continues to grow down the estuary, but near the causeway has stabilized, and portions of the
mudflat appear to have become important feeding grounds for migratory birds and fish. Expansion of the Windsor Causeway to accommodate twinning of Highway 101 may involve construction affecting a significant portion this mudflat, with important shortterm
ecological consequences. Present knowledge is insufficient to assess the degree of impact of the expansion on biophysical processes and biological resources in the estuary. In the summer of 2003, the Acadia Centre for Estuarine Research conducted research on
the fish populations above and below the Windsor Causeway. Additional studies were made together with Dr. Danika van Proosdij (Saint Mary’s University, NS), on salt marsh growth, and invertebrate populations of the marsh-mudflat complex that has developed
on the seaward side of the Causeway, and the first investigation of a second intertidal mudflat (the Newport Bar), that has formed on the seaward side of the St. Croix outflow channel.
The present study focused on the following aspects:
a) Occurrence of diadromous fish in the Avon Estuary, Pesaquid Lake and the lower
Avon River;
b) Occurrence of larval fish in Pesaquid Lake and the lower Avon River;
c) Fish utilization of the channels and mudflats on the seaward side of the Windsor Causeway;
d) Physicochemical conditions in Pesaquid Lake and the lower Avon River, and flow conditions at the Causeway gates.
1. A total of 763 fish were captured in the West and Causeway Channels on the seaward side of the Causeway, using gill nets, a fyke net, and eel pots, between 22 May and 30 July 2003. These represented six species: alewife (Alosa
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pseudoharengus), blueback herring (Alosa aestivalis), striped bass (Morone
saxatilis), white perch (Morone americana), tomcod (Microgadus tomcod) and American eel (Anguilla rostrata).
2. The gaspereau run, which consisted of both alewife and blueback herring, lasted from before 22 May, when the nets were first set, until the first week of July. The first part of the run consisted mostly of alewives, whereas blueback herring were
more common than alewives during June. The age of migrant fish was three to seven years for alewives, and three to six years for blueback herring.
3. Striped bass were only captured on the seaward side of the Causeway. They ranged from two to five years of age, and were not engaged in a spawning run. Stomach contents indicated that they feed on epibenthic animals, especially the
shrimps Crangon septemspinosa and Neomysis americana.
4. Gill net and seine collections above the Causeway in Pesaquid Lake and the lower Avon River were carried out from late May to early October. More than 2,000 fish were taken in total, representing 11 species. The only anadromous species
caught above the Causeway were alewife, blueback herring, and white perch. No salmonids (salmon or trout) or smelt were captured by any technique.
5. Young of the year gaspereau were captured by seine in Pesaquid Lake until early October, but numbers declined sharply in September when fish either moved away from shore or out to sea.
6. Length—weight relationships and seasonal changes in body length of the most abundant species – banded killifish, alewife and blueback herring – suggest that growth conditions in the Lake and its tributaries are good.
7. Physico-chemical studies in the lower Avon River and Pesaquid Lake provided no information of eutrophication – nutrient enrichment that results in a decrease in water quality – in spite of land use (agriculture, golf course maintenance, residential development) in the watershed of the Lake. Although nitrogen and phosphorous levels in Pesaquid Lake were higher than in the main river inflows,
these were not sufficient to trigger excessive plant growth. Plankton studies, however, indicated that the Lake is quite productive.
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8. Measurements of flow through the Causeway gates when opened to facilitate fish passage, indicated that peak velocities in excess of 7 metres/second were reached in the middle of the gate opening. Such velocities exceed the swimming capacity of gaspereau, but their upstream migration was successful in part because there were lower velocities for a period of many minutes following gate opening, and
possibly because velocities near the side of the canal were significantly lower than in the centre. It is suggested that a study of when migrating gaspereau approach the gates on the rising tide would enable development of an optimal plan for gate operation that would facilitate upstream movement.
9. A preliminary survey of the Newport Bar, a mudflat that is separated from the Windsor Causeway marsh—mudflat by a channel of the St. Croix Estuary, indicated that it has a well developed benthic fauna that is dominated by Corophium volutator. Abundance of Corophium on this bar approaches the higher values associated with other productive mudflats in Minas Basin that are frequented by migratory shorebirds. Observations indicated that this bar has become the principal feeding area for semipalmated sandpipers in the upper Avon
Estuary. However, patches of salt marsh (Spartina alterniflora) have become established on the bar, and, unless removed by ice or other forces, it is expected that the patches will coalesce and the bar undergo succession to a salt marsh in the same way as the area adjacent to the Causeway.