Fishing Gear Entrapments Leading Cause of Atlantic Whale Deaths

crabFrom Science Magazine

On Christmas Day 2010, an aerial team of wildlife spotters saw a whale in distress off the eastern coast of Florida. Her head, mouth, and fins were tangled in 132 meters of commercial fishing rope. Marine veterinarians and biologists untangled the whale, diving into the water and cutting the lines that had wrapped around her upper jaw and cut into her flesh. But the damage had been done. Weeks later, the giant mammal was found floating at the surface, the victim of a shark attack. The incident, according to a new study, shows that whales’ fight against fishing gear can kill them long after they’ve been freed from it.

Researchers already know that heavy-duty commercial fishing lines and lobster and crab traps, connected to the surface by long ropes, pose a formidable threat to whales in the North Atlantic, by inflicting deep wounds and sapping their energy reserves. Accidental entrapment is the leading cause of death for Atlantic whales in records going back to 1970. The National Marine Fisheries Service reported 25 sightings of entangled whales in 2010. Five did not survive the encounter. Many of the surviving whales were described as thin and weak.

The whale spotted on Christmas, a 2-year-old female right whale cataloged as Eg 3911 (Eg for the species’ scientific name, Eubalaena glacialis), tangled with a fishing trap line sometime between February and December 2010. By the time researchers rescued her on 15 January 2011, she was 20% thinner than other right whales her age. The team suspects she wasn’t able to dive deep enough to reach the plankton and crustaceans she’d normally feed on.

Once liberated, Eg 3911 began swimming faster and diving deeper, but she had no way to bulk back up. Right whales normally feed in cool northernrope waters during the summer, and Florida’s winter waters offered no food sources. “You’re tired, you’re hungry, you’re really skinny, and there’s nothing for you to eat,” says Julie van der Hoop, a marine mammal biologist at the Woods Hole Oceanographic Institution in Massachusetts and lead author of a new paper documenting the incident. Eg 3911 was found dead in the water on 1 February, sporting lethal shark attack wounds. Van der Hoop suspects that the whale was lethargically bobbing at the surface when she was bitten.

Following Eg 3911’s death, van der Hoop and colleagues wondered how much the gear taxed the emaciated whale’s energy reserves. Scientists lowered some of the very fishing gear removed from Eg 3911 into the water behind a moving skiff to estimate how much drag the lines and buoys generated, and how much energy the whale would have to expend to compensate. They estimated that Eg 3911 was burning up to twice as much energy while entangled. Their results appear online this week in Marine Mammal Science.

The team doesn’t know how long Eg 3911 was entangled—it could have been only weeks, or closer to a year. Whales can live with the tight, cutting, restricting lines for 6 months to a year before succumbing to injury, infection, or starvation, van der Hoop says. “That is a really long time to be subject to this type of injury.”

Long-term consequences may linger long after entrapment, even when whales return to health. Marine mammal biologist Scott Kraus of the New England Aquarium in Boston, who was not involved in the study, says that he plans to use these results to reexamine the life history of whales postentanglement. “We’ve tended to think that entangled animals either get free or die,” he says. “The sublethal effects of entanglement have not been considered.”

Kraus says that he’s learned a sobering lesson from Eg 3911’s story—whales are not home free once they’re loosed from entangling lines. “The impact of humanity on these creatures does not end when they go out of sight.”

Categories: Entangled Marine Mammals, Fisheries, Fishing Lines, Ghost Nets, Marine Mammal Rescue, Whales

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