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Science 15 December 2006:
Vol. 314. no. 5806, pp. 1773 - 1776
DOI: 10.1126/science.1135347
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Reports

Biomass, Size, and Trophic Status of Top Predators in the Pacific Ocean

John Sibert,1* John Hampton,2 Pierre Kleiber,3 Mark Maunder4

Fisheries have removed at least 50 million tons of tuna and other top-level predators from the Pacific Ocean pelagic ecosystem since 1950, leading to concerns about a catastrophic reduction in population biomass and the collapse of oceanic food chains. We analyzed all available data from Pacific tuna fisheries for 1950–2004 to provide comprehensive estimates of fishery impacts on population biomass and size structure. Current biomass ranges among species from 36 to 91% of the biomass predicted in the absence of fishing, a level consistent with or higher than standard fisheries management targets. Fish larger than 175 centimeters fork length have decreased from 5% to approximately 1% of the total population. The trophic level of the catch has decreased slightly, but there is no detectable decrease in the trophic level of the population. These results indicate substantial, though not catastrophic, impacts of fisheries on these top-level predators and minor impacts on the ecosystem in the Pacific Ocean.

1 Joint Institute for Marine and Atmospheric Research, University of Hawaii, Honolulu, HI 96822, USA.
2 Oceanic Fisheries Programme, Secretariat of the Pacific Community, BP D5, Noumea 98848, New Caledonia.
3 Pacific Islands Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 2570 Dole Street, Honolulu, HI 96822, USA.
4 Inter-American Tropical Tuna Commission, 8604 La Jolla Shores Drive, La Jolla, CA 92037, USA.

* To whom correspondence should be addressed. E-mail: sibert{at}hawaii.edu

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