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Fisheries impacts on marine ecosystems and biological diversity : the role for marine protected areas in British Columbia

University of British Columbia

This research examines the impacts of fishing on marine ecosystems and marine biodiversity in British Columbia, Canada and examines the role of marine protected areas (MPAs) in mitigating these impacts. A variety of ecological approaches are taken to understand fisheries impacts. First, a catch database of historical landings in British Columbia was assembled covering the years between 1875 and 1996 for all species in all fisheries. It was shown that combined landings of all species have been very high for nearly 80 years, but the composition has changed dramatically primarily due to overfishing. Using the catch database, an assessment of large-scale ecosystem changes from overfishing was determined by a mean trophic level analysis and an estimation of marine primary productivity requirements to sustain the fishery. The mean trophic level of the catches in British Columbia's fisheries has steadily declined since the 1950's indicating an erosion of ecosystem structure from the systematic removal of long-lived, non-migratory, high trophic level species. Primary productivity requirements of the fishery as a whole has remained very high, although the relative contributions of each species group has changed significantly demonstrating fishing impacts on biodiversity and ecosystem structure. Two ecosystem models of the Strait of Georgia, one of present day and the other of 100 years ago, were developed using Ecopath software to demonstrate fishing induced changes at an ecosystem level. Results show that many species have been depleted to a point where they no longer have a functional ecosystem role in the Strait. Overall, the ecosystem is considered to be quite mature due to a substitution of higher valued commercial fish, to low value under-exploited fish occupying the same trophic niche. This was demonstrated by a trophic level analysis which indicated that virtually no high trophic level, resident species are found in present day fisheries landings. Marine protected areas were examined as tools to rebuild ecosystem structure by performing field-based studies on two severely depleted species found in the Strait, northern abalone (Haliotis kamtschatkana) and lingcod (Ophiodon elongatus). It was shown that populations of both species respond positively to the absence of human harvest in a defined area. These findings suggest that other species, and entire ecosystems may benefit from the creation of MP As. It was concluded that fisheries have had enormous impacts on marine ecosystem structure in British Columbia waters and that MP As offer one tool to restore, protect, and conserve marine resources.

Thesis/Dissertation

application/pdf

2009-07-03

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http://hdl.handle.net/2429/10080

Resource Management and Environmental Studies

University of British Columbia

UBCV

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