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Study Shows Eastern Tropical
NOAA Study Shows Eastern Tropical Pacific Ocean Dolphin Populations Improving
Two Dolphin Stocks May Be Recovering from Tuna Fishing Practices
June 5, 2008
 The
numbers of northeastern offshore spotted
and eastern spinner dolphins in the eastern
tropical Pacific Ocean are increasing after being severely
depleted because of accidental death in the tuna purse-seine
fishery between 1960 and 1990, according to biologists from
NOAA’s Fisheries Service.
“These estimates are encouraging because
they are consistent with what we would expect to see if these
stocks are recovering, now that reported fishery mortality
has been dramatically reduced,” said Dr. Lisa Ballance, director
of NOAA’s Southwest Fisheries Science Center
protected resources division. “However, we have to be careful
not to jump to final conclusions. We need to resolve the uncertainties
around these estimates before we can definitively say these
stocks are recovering.”
Between 1960 and 1990, the northeastern
offshore spotted and eastern spinner dolphin populations
dropped to 20 percent and 30 percent, respectively, of their
pre-fishery levels when dolphins were caught and died in tuna
purse-seine nets. Since the early 1990s, however, the number
of reported dolphin deaths has been very low because of severe
restrictions on the fishery.
“We expected to see these populations begin their recovery years ago, because fishermen have been so successful at reducing dolphin deaths,” said Tim Gerrodette of NOAA’s Fisheries Service. “The new data are the first to indicate the beginning of a recovery, but these initial indications are not enough to be confident that the populations will continue to grow.”
 Researchers emphasize the need to continue to monitor dolphin populations at sea through comprehensive ecosystem research cruises, and to conduct an updated dolphin stock assessment that will include not only these most recent abundance estimates, but also additional information on dolphin life history, fishery mortality, and the ecosystem. This assessment will enable a more definitive interpretation of whether these abundance estimates indicate Eastern Tropical Pacific dolphins are recovering and the degree to which the fishery and other factors affect the conservation of these stocks.
Today’s report stems from a series of research cruises conducted since 1986. It presents new estimates of abundance for 10 dolphin stocks for each survey year between 1986 and 2006. These estimates may be found at http://swfsc.noaa.gov/prd-etp.aspx.
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