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Publication year : 0
Thematic : Fisheries
Language : English
Note
Pelagic fisheries in the Pacific Ocean target both large (Thunnus spp.) and small tunas (juveniles of Thunnus
spp; Katsuwonus pelamis) but also take billfishes (Xiphias gladius, Makaira spp., Tetrapturus spp., Istiophorus
platypterus) and sharks (Prionace glauca, Alopias superciliosus, Isurus oxyrinchus, Carcharhinus longimanus,
Galeocerdo cuvieri) as bycatch. We developed a multispecies model using the Ecopath with Ecosim software that
incorporated time-series estimates of biomass, fishing mortality, and bycatch rates (1952–1998) to evaluate the relative
contributions of fishing and trophic impacts on tuna dynamics in the central Pacific (0°N to 40°N and 130°E to
150°W). The Ecosim model reproduced the observed trends in abundance indices and biomass estimates for most large
tunas and billfishes. A decline in predation mortality owing to depletion of large predators was greatest for small
yellowfin tuna and could possibly account for apparent increases in biomass. For other tunas, however, predicted
changes in predation mortality rates were small (small bigeye) or were overwhelmed by much larger increases in
fishing mortality (skipjack and small albacore). Limited evidence of trophic impacts associated with declining apex
predator abundance likely results from the difficulties of applying detailed trophic models to open ocean systems in
which ecological and fishery data uncertainties are large.
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Keywords : Rhinolophus sinicus
Encoded by : Pauline Carmel Joy Eje
