Tuna Nets Entangling Fewer Dolphinsff

Source: Discovery Channel

The most recent dolphin counts in the eastern tropical Pacific Ocean suggest that two species decimated by deaths in tuna fishing nets may be making a comeback.

Populations of the northeastern offshore spotted dolphin and the eastern spinner dolphin plummeted by 80 and 70 percent, respectively, between 1960 and 1990, as they were caught in nets set for tuna. More than six million dolphins have died this way since the late 1950s.

Thanks to increasingly strong regulations to prevent these deaths passed in the 70s, 80s and 90s, dolphin deaths have declined drastically, with fewer than 1,000 dolphins now dying a year in nets.

”Because they were so good at reducing the mortality, we’ve been expecting the population to recover for quite some time now,” said Jeremy Rusin, of the National Oceanic and Atmospheric Association’s Southwest Fisheries Science Center in La Jolla, Calif.

It took longer than expected to see improvement, but the latest survey, conducted in 2006, estimates the northeastern offshore spotted dolphin population at 857,884, up from 822,157 in 2003, and 636,780 in 2000. NOAA estimated the eastern spinner dolphin population at more than 1.06 million in 2006, compared with 673,943 in 2003.

Although the counts show an increase, Rusin emphasized that the results do not indicate a conclusive trend. The large area covered by the survey -almost the size of North America- means the estimates carry large uncertainty.

”We need additional surveys to be sure that the increases we’ve seen this year are real increases, and not just the reflection of statistical uncertainty,” Rusin said.

One group of dolphins, the western/southern spotted dolphins, continued to decline. This finding, coupled with the rise of the northeastern offshore spotted dolphin, may simply be explained by a migration of some individuals from one zone to another, Rusin said.

The fact that recovery has been slow may indicate that even with new measures in place, dolphins continue to suffer in other ways from the tuna fishery.

Yellowfin tuna swim with dolphins, so fishermen often use dolphin sightings to locate tuna. Then they chase and surround the dolphins with nets to capture the tuna beneath.

Previously, they would scoop up the dolphins along with the fish, but since the regulations took hold they drive their boat in reverse after surrounding the dolphins, to force the nets beneath the dolphins at the water’s surface. This approach, known as backdown, lets the dolphins out while still trapping the tuna inside.

But some other aspects of the chase may be slowing recovery.

”Even though the vast majority of dolphins caught in nets are now released alive, scientists believe that repeated chases and separation of mothers from calves continue to stress these dolphins and affect their ability to recover to pre-fishery levels,” said Vicki Cornish of the Ocean Conservancy in Washington, D.C.

In the United States, tuna cannot be labeled “dolphin safe” if dolphins are chased at all, even if the backdown method is used. But one of the main alternative methods -- using “fish aggregation devices” that, like dolphins, lure tuna to school beneath -- is not without problems, Cornish said.

”The problem with fish aggregation devices is there’s a higher bycatch on turtles and sharks and smaller tuna.”

”It’s encouraging to see that maybe the dolphin stocks are starting to bounce back,” she said. “We need to continue to find fishing techniques that do not affect other species.”