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MEPS 291:1-21 (2005)
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Abstract
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Non-recovery of two spotted and spinner dolphin populations in the eastern tropical Pacific Ocean
Tim Gerrodette1,*,**, Jaume Forcada1,2
1NOAA Fisheries, Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, California 92037, USA
2Present address: British Antarctic Survey, Natural Environment Research Council, Madingley Road, Cambridge CB3 0ET,
UK
*Email: tim.gerrodette@noaa.gov
**Order of authorship determined by flip of a coin.
ABSTRACT: Populations of northeastern offshore spotted dolphins Stenella attenuata attenuata and eastern spinner dolphins S. longirostris orientalis have been reduced because the dolphins are bycatch in the purse-seine fishery for yellowfin
tuna in the eastern tropical Pacific Ocean (the 'tuna-dolphin issue'). Abundance and trends of these dolphin stocks were assessed from 12 large-scale pelagic surveys carried out between 1979 and 2000. Estimates of abundance were based on a multivariate
line-transect analysis, using covariates to model the detection process and group size. Current estimates of abundance are about 640 000 northeastern offshore spotted dolphins (CV = 0.17) and 450 000 eastern spinner dolphins (CV = 0.23). For the whole
period from 1979 to 2000, annual estimates of abundance ranged from 494 000 to 954 000 for northeastern offshore spotted dolphins and from 271 000 to 734 000 for eastern spinner dolphins. management actions by USA and international fishing agencies over 3
decades have successfully reduced dolphin bycatch by 2 orders of magnitude, yet neither stock is showing clear signs of recovery. Possible reasons include underreporting of dolphin bycatch, effects of chase and encirclement on dolphin survival and
reproduction, long-term changes in the ecosystem, and effects of other species on spotted and spinner dolphin population dynamics.
KEY WORDS: Bycatch · tuna-dolphin issue · abundance · eastern tropical Pacific · Stenella attenuata · Stenella longirostris · Population recovery · fishery interactions
Full text in pdf format
Published in MEPS Vol.
291
(2005) on April 28
Print ISSN: 0171-8630; Online ISSN: 1616-1599.
Copyright © Inter-Research, Oldendorf/Luhe, 2005
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