MEPS 404:289-302 (2010)  -  doi:10.3354/meps08443

Ecosystem models clarify the trophic role of whales off Northwest Africa

Lyne Morissette1,2,*, Kristin Kaschner3, Leah R. Gerber2

1Institut des sciences de la mer de Rimouski, 310, Allée des Ursulines, C.P. 3300, Rimouski, Quebec G5L 2Y9, Canada
2School of Life Sciences, Arizona State University, Box 874501 Tempe, Arizona 85287-4501, USA
3Evolutionary Biology & Ecology Lab, Institute of Biology I (Zoology), Albert-Ludwigs-University Freiburg, Germany

ABSTRACT: There is global concern about the interaction between whales and fisheries, and in some countries, great whales are viewed as a threat to fisheries by potentially eating fish species that could be exploited for human consumption. We developed an ecosystem model to explore the trophic interactions between cetaceans and fisheries off Northwest Africa and to examine the potential impact of a reduction in the abundance of baleen whales on fishery yields. This allowed us to characterize the structure and function of the ecosystem in terms of biomass, mortalities, consumption rates, food habits, and fisheries. Faced with sparse data for our study area, we explicitly accounted for uncertainty in ecosystem structure, model accuracy, and input data and conducted an extensive sensitivity analysis. We tested model performance with time series of biomass and catches for important species of the system. Our results indicate that the overlap between prey species consumed by cetaceans and species targeted in fisheries is low. Furthermore, for a wide range of assumptions about whale abundances, diet composition, and food consumption in breeding areas, we found that whale consumption is several orders of magnitude lower than total fishery catches and 2 orders of magnitude lower than the amounts taken by other trophic groups. Finally, simulations of substantial reductions of whale populations did not influence the biomass of commercially important fish, nor any other species of the foodweb. These results suggest that fisheries yields would not benefit from the removal of whales in this area.

KEY WORDS: Competition · Ecopath with Ecosim · Cetaceans · Predation · Trophic impacts · Marine mammal-fisheries interactions . Ecosystem modeling

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Cite this article as: Morissette L, Kaschner K, Gerber LR (2010) Ecosystem models clarify the trophic role of whales off Northwest Africa. Mar Ecol Prog Ser 404:289-302

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