Change in trophic structure of a shelf ecosystem in the northwest Atlantic during a period of increased fishing pressure
Multi-species and ecosystem modelling are increasingly touted as essential approaches in the future of fisheries management. These methodologies can involve the amalgamation of data on the landings, biomass, consumption, production, and diets of many species or species groups in current time, the fu...
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| Format: | Thesis |
| Language: | English |
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Memorial University of Newfoundland
2005
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| Online Access: | https://research.library.mun.ca/10064/ https://research.library.mun.ca/10064/1/Alcock_Erin.pdf |
| Summary: | Multi-species and ecosystem modelling are increasingly touted as essential approaches in the future of fisheries management. These methodologies can involve the amalgamation of data on the landings, biomass, consumption, production, and diets of many species or species groups in current time, the future and in the re-examination of the past. The Ecopath approach was used to construct two mass balance ecosystem models for the southern Labrador Shelf, Northeast Newfoundland Shelf and Grand Bank in Northwest Atlantic Fisheries Organisation (NAFO) Divisions 2J+ 3KLNO the first for the time period 1954-1956 and the second for 1968-1970. Our models increased the temporal resolution of ecosystem models developed by The Fisheries Centre at the University of British Columbia. The start (1950s) and rapid expansion (1960s) of industrial harvesting by factory freezer trawlers during these time periods resulted in massive increases in fishing effort, the total catch increased by 30%, and there was extensive spatial intensification and expansion, particularly on the Labrador Shelf. Biomass declines in adult and juvenile Atlantic cod, harp seals, and their main prey species capelin and sandlance were evident. A change in predator/prey relationships between the two time periods was expected, but not found. An increase in the biomass of some invertebrate species groups was expected, but not evident, possibly due to sparse historical data. System ratios and indicators pointed to the latter ecosystem as nearer to a state of being 'fished down', perhaps indicating the onset of the trophic shift evident in the late 1980s and 1990s. |
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