For the first time in about 30 years, dolphin populations endangered by fishing practices are springing back, due to an Agreement on the International Dolphin Conservation Program (AIDCP).
“We expected the populations to recover earlier,” said Jeremy Rusin, deputy director for Protected Resources, National Oceanic Atmospheric Administration (NOAA), Southwest Fisheries Science Center (SFSC), La Jolla. “It’s a little bit later than we expected, but the dolphin population is recovering so we’re optimistic.”
La Jolla scientists announced results from an ongoing study that said two dolphin species “” the spinner and spotted dolphins “” seem to be recovering from damage the tuna industry inflicted on them beginning in the 1960s and ’70s. The populations of those two species dropped 20 and 30 percent between 1960 and 1990, when dolphins were caught and died in tuna purse-seine nets, said a NOAA press release. Since then, the number of reported dolphin deaths has been very low because of severe restrictions on the fishery, NOAA reported.
Scientists and researchers from the NOAA fisheries at La Jolla began studying the dolphin populations in 1986, seeking reasons for the species’ decline, Rusin said.
Yellowfin tuna have a symbiotic relationship with many species of dolphin in the tropical waters of the Eastern Pacific, according to NOAA. Because of the “dolphin-tuna bond,” fishermen use a technique they call “porpoise fishing.” The tuna fishermen spot dolphins and, because of their association with tuna, chase, capture and then release the dolphins using a backdown procedure “” while keeping the tuna inside the net.
According to NOAA, after officials began regulating the tuna industry, they saw a significant change in the dolphin mortality rate; by the end of the 1970s, the number of dolphins killed was reduced from 500,000 to 20,000 per year.
“The issue with dolphins being depleted was a U.S. fishery issue at one time, then it became an international issue,” Rusin said.
According to Rusin, independent observers working for the U.S. government began to accompany tuna fishermen, counting the number of dolphins killed on fishing trips. The observer program established annual limits on dolphin mortality, whichs provided an incentive for fishermen to release dolphins unharmed, using the backdown procedure that involves towing the net in reverse until dolphins were safely out, Rusin said.
Rusin attributes the species’ rise to tuna fishermen and their willingness to take part in the AIDCP.
“The fishermen deserve a lot of credit for reducing the number of dolphins killed in the fishery,” Rusin said. “One of the ways they’ve reduced dolphin deaths is through their ingenuity ” for example, through the backdown procedure.”
In addition to tuna industry procedures, the AIDCP initiated the observer program, the annual dolphin mortality limits and the dolphin safe tuna program, which has different standards in various countries, Rusin said. The agreement includes the countries Costa Rica, Ecuador, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, Peru, United States, Vanuatu and Venezuela; Bolivia, Columbia and the European Union are also “applying the agreement provisionally,” Rusin said.
Despite results from the new study, researchers are apprehensive about affirming that dolphin populations are recovering. La Jolla scientists continue to study the species during routine research trips.
Scientists from the SFSC at La Jolla depart from San Diego every three years on research vessels “” two NOAA ships “” for 240 sea-days. They head toward the Hawaiian Islands, then to Peru and along the coast of the Americas, into the tropical waters of the Pacific Ocean where they study 21 million square kilometers (8.1 million square miles) of ecosystem and dolphin populations.
“We look at where we see dolphins in the ecosystem and changes in the ecosystem,” Rusin said. “It helps us see the effects of the fishery on dolphin populations. When we were looking at why they were not recovering like we expected, we asked if it was something else.”
The teams studied the ecosystem, trying to determine if another cause was deterring the dolphin populations from recovering, but they did not come to that conclusion, Rusin said.
Researchers are asking why dolphins have taken this long to recover. They said they have a lot of questions and aren’t stating for certain the populations are home free just yet.
Biologists from the fisheries at La Jolla will study dolphin numbers again next year, when another mission is scheduled.
“Because we have this time series of data, we want to avoid saying these dolphins have recovered,” Rusin said. “We’re working with the fishermen to reinforce what they’re doing is a good thing.”