Robert Gregory
Research Scientist, Fisheries & Ocean Canada, Northwest Atlantic Fisheries Centre
Coastal Nurseries
The importance of coastal nurseries to offshore fish production is mediated by habitat and environmental changes, affecting vital rates which are often habitat-specific and, therefore, influence population regulating processes such as growth and density-dependent survival. This project aims to investigate five hypotheses concerning the loss of coastal zone habitat, effects of temperature change on production of adult fish, possible effects of management intervention on cod population stability, and cumulative effects of habitat loss and temperature rise due to climate change by using seven extensive multiyear databases.
Coastal nursery habitats (e.g., eelgrass patches, Zostera marina) contribute fish to adult populations which may then be harvested by capture fisheries. It has often been assumed that the abundance of young originating from individual nurseries contributes proportionately to the adult population. Although this principle is intuitive, it has proven been difficult to test due to temporal and spatial disconnects between adult fish and their young. Coastal zone nursery surveys offer several attractive advantages to surveys of adult fish, including 1. early forecasting of recruitment; 2. effective spatial coverage; 3. enables collection of “vital rates” (i.e., growth, survival, dispersal) at earlier life stages that are typically influenced by fisheries; and, 4. allows early warning to pending changes in vital rates due to cumulative impacts from natural and anthropogenic stressors. The importance of coastal nursery habitats – e.g., eelgrass (Zostera marina), and other macrophytes – to offshore fish production is mediated by habitat and environmental changes, inducing changes in vital rates among fish species. These rates are often habitat-specific and affect population regulating processes such as growth and density-dependent survival, often in response to temperature.
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Simulation studies to estimate vital rates for the models of habitat-mediated dispersal and temperature effects on overwinter mortality and recruitment among age groups within cohorts are completed.
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Field studies to validate model assumptions are in progress.
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Modelling the effects of rising summer temperatures and their likely influence the spatial distribution of affected fishes on the Grand Bank of Newfoundland and the Eastern Scotian Shelf off Nova Scotia in progress.
