Research Document - 2014/047

Indicators of Pelagic Habitat Status in the Northwest Atlantic

By Catherine Johnson, Pierre Pepin, K. Alexandra Curtis, Gordana Lazin, Benoit Casault, Eugene Colbourne, Peter S. Galbraith, Michel Harvey, Dave Hebert, Gary Maillet, and Michel Starr

Abstract

Regional changes in pelagic (i.e. water column) habitat, including the physical and chemical environment and plankton abundance and community composition, may influence productivity of fisheries at regional scales. The analysis presented here used principal component analyses (PCA) to characterize the dominant patterns of variability in zooplankton communities and the environment at the scale of the Canadian northwest Atlantic continental shelf system from the Labrador Shelf to the eastern Gulf of Maine. The analyses used data collected by the Atlantic Zone Monitoring Program in Fisheries and Oceans Canada’s Newfoundland, Gulf, Québec, and Maritimes regions. As a case study on using pelagic habitat status indicators to understand variability in fishery status, the principal component scores, climate indices and sub-regional-scale environmental and plankton metrics were compared with interannual changes in the distribution, condition, and recruitment of eastern Gulf of Maine and Scotian Shelf herring. The zooplankton PCAs in spring and fall identified depth and cross-shelf associations as the dominant mode of community variability, followed by temperature and seasonal associations and regional differences between the Gulf of St. Lawrence and open shelf communities. The environmental PCAs in spring and fall identified variability in nutrient inventories as the dominant mode of variability, with high values in the northwest Gulf of St. Lawrence in both seasons and north of the Grand Bank in spring. The second mode of environmental variability generally differentiated warm, salty deep water from shallow water with higher excess nutrients in both seasons, while the third mode was associated with higher chlorophyll and lower excess silicate in cooler waters and differentiated the Newfoundland Shelf and Grand Bank from the Gulf of St. Lawrence in spring and from the Scotian Shelf in fall. Herring condition metrics in the Scotian Shelf subregions were positively correlated to one another and negatively correlated to herring distribution on the Eastern Scotian Shelf. Scotian Shelf herring were generally in better condition under cooler, higher nutrient environmental conditions consistent with increased outflow from the Gulf of St. Lawrence onto the Scotian Shelf. Eastern Gulf of Maine herring metrics had few consistent correlations to environmental factors, suggesting that the condition and recruitment of these stocks, sampled on their spawning grounds, did not have a common response to large scale pelagic habitat variability. However, the dominant copepod species Pseudocalanus spp. and, to a lesser extent, Calanus finmarchicus, known to be important prey for herring, were positively correlated to many herring metrics in ordered factors correlation analyses, which emphasize extreme values of the herring and environment metrics. The influences of large-scale and regional processes on the shelf system were evident in the patterns that emerged from the zooplankton and environmental multivariate analyses. The short time series available had low power to identify relationships between pelagic habitat and herring metrics, but allowed the identification of relationships that could be further examined using longer time series of representative environmental metrics.

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