May 22, 2013
Whale’s Slow Death Caused By Fishing Gear
Brett Smith for redOrbit.com — Your Universe Online
While bans against whale hunting have greatly reduced the direct threat fishermen pose to the marine mammals, a new study in the journal Marine Mammal Science points to a deadly indirect threat — potential entanglement in fishing lines.
In the study, the research team tracked Eg 3911´s movements before, during, and after at-sea disentanglement operations with an attached cellphone-sized device called a Dtag.
“The Dtag opened up a whole new world of Eg 3911´s life under water that otherwise we weren´t able to see,” said lead author Julie van der Hoop, a graduate student in the MIT/WHOI Joint Program in Oceanography.
A tangled and gaunt Eg 3911 was first spotted by an aerial survey team on Dec. 25, 2010, near Jacksonville, Florida. At the time, the female right whale had fishing gear wrapped around her mouth and both pectoral fins.
Rescue teams attempted to remove the fishing gear on December 29 and 30, but were unsuccessful because the whale was uncooperative. Before trying again on Jan. 15, 2011, another team applied a Dtag. Next, they administered a sedative, allowing the team to cut away almost all the fishing equipment.
After being released, the whale was observed making 152 dives over six hours.
“The near-complete disentanglement of Eg 3911 resulted in significant increases in dive duration and depth,” the study authors wrote. “Together, the effects of added buoyancy, added drag, and reduced swimming speed due to towing accessory gear pose many threats to entangled whales.”
“Most significant, however, is the energy drain associated with added drag,” they added.
To calculate the potential energy drain, the scientists towed three types of fishing gear from a boat and used tension meters to measure the resulting drag forces. They then determined how much more energy would be required by the whales to overcome drag caused by the fishing equipment.
The team found that entangled whales expend significantly more energy, either requiring 70 to 102 percent more power to swim at the same speed or slowing down by 16 to 20.5 percent.
Unfortunately, an aerial survey observed Eg 3911 dead at sea on Feb. 1, 2011. She would later be towed to shore for a necropsy.
“We showed up on the beach that night. I remember walking out there and seeing this huge whale, or what I thought was huge,” van der Hoop said. “She was only 10 meters long. She was only two years old. And all these people who had been involved in her life at some point, were there to learn from her what entanglement had caused.”
The results of the necropsy pointed to complications from chronic entanglement as the cause of death.
“No fisherman wants to catch a whale, and I wish no fisherman a hungry day,” said study co-author Michael Moore, director of the Marine Mammal Center at WHOI. “There needs to be a targeted assessment of how the fishery can still be profitable while deploying less gear so we can reduce the risk of marine mammals encountering fishing gear in the first place.”
“At WHOI, we have hosted workshops talking with fisheries managers and fishermen about what might change so that they can continue to catch fish and stop catching whales,” he added.