Two Eastern Tropical Pacific Dolphin Species Recovering

For unknown reasons, dolphins swim with schools of tuna. Fishermen used them to locate the fish, then the dolphins were caught up in the nets along with the target tuna and drowned.

Since the early 1990s, however, the number of reported dolphin deaths has been low because of severe restrictions on the fishery that were accompanied by dolphin-safe tuna labeling laws. The labels were placed on cans of tuna caught without harm to dolphins, which were preferred by many consumers.

Even so, the dolphins have been slow to recover, according to scientists with the National Oceanic and Atmospheric Adminnistration, NOAA.

"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 National Marine Fisheries Service, one of the report's authors.

Spinner dolphins in the Eastern Tropical Pacific Ocean (Photo courtesy NOAA SFSC)

"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," he said.

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.

Today's report stems from a series of research cruises conducted since 1986 in a large area west of Mexico and Central America. It presents new estimates of abundance for 10 dolphin stocks for each survey year between 1986 and 2006.

The most abundant dolphins in the study area were short-beaked common dolphins, which numbered about 3.13 million in 2006.

The least abundant were rough-toothed dolphins, which numbered about 108,000 and Risso's dolphins, numbering 110,000 in 2006.

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.

"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 and co-author of this study.

"However, we have to be careful not to jump to final conclusions," she said. "We need to resolve the uncertainties around these estimates before we can definitively say these stocks are recovering."

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