© 2004 International Council for the Exploration of the Sea
Balancing exploitation and conservation of the eastern Scotian Shelf ecosystem: application of a 4D ecosystem exploitation index
a Fisheries and Oceans Canada, Science Branch PO Box 1006, Dartmouth, Nova Scotia, Canada B2Y 4A2
b Food and Agriculture Organization, Sub-regional Office for the Caribbean PO Box 631-C, Bridgetown, Barbados
*Correspondence to A. Bundy: tel: +1 902 426 8353; fax: +1 902 426 1506. e-mail: bundya{at}mar.dfo-mpo.gc.ca.
Few indicators exist that measure the effects of fishing at the whole-ecosystem level. A 4D ecosystem exploitation index is proposed that integrates four measures of ecosystem status: (i) the trophic balance of exploitation, (ii) the intensity of exploitation, (iii) species richness, and (iv) disturbance of the trophic structure. The central concept is that fisheries should extract yield in proportion to the productivity at each trophic level, at sustainable exploitation rates, with minimal disturbance to the trophic structure, and with no loss in species richness. The ecosystem exploitation index is tested on simulated ecosystem data and applied to data from the eastern Scotian Shelf, Canada. The model simulations provided consistent results that should facilitate cross-system comparisons of exploitation and ecosystem status. When applied to actual observations, the results were less coherent, likely attributable to lag effects and environmental impacts. All fisheries likely alter the trophic structure of ecosystems, and the rate and trophic pattern of exploitation determines the level of change. Exploiting all trophic levels equally would always result in less change to trophic structure than top-heavy exploitation. Further testing is required to determine lag effects and sensitivity to various assumptions.
Keywords: disturbance index, ecosystem exploitation index, ecosystem indicator, species richness, trophic balance index, trophic level
Received 1 April 2004; accepted 29 November 2004.
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