Fishing net injury 'disables' minke whale

Matt Walker, BBC News 15 Jun 09;

An injured minke whale has provided a unique insight into the dangers posed to marine animals by fishing gear.

The minke whale was spotted off the coast of Quebec, Canada, with a huge scar around its throat thought to be caused by floating rope. What's more, it fed in a way never before recorded for minke whales, probably in response to its injury.

The sighting is one of the first to detail the handicaps that can be caused to animals that become entangled.

Earth News reports the development as part of a series of articles highlighting the dangers fishing nets pose to marine animals.

Previously, we described how

Now marine biologist Brian Kot of the University of California and colleagues working for the Mingan Island Cetacean Study non-profit research organisation have published details in Marine Mammal Science of a minke whale that has been badly scarred by fishing gear.

Spotted of the coast of Longue-Pointe-de-Mingan, Quebec, in the Gulf of St Lawrence, the minke whale had a deep laceration running the circumference of its feeding pouch, from near its throat up both sides of its head close to each eye.

The cut ran through the whale's skin and into its blubber, in parts exposing the muscle underneath.

"The width of the laceration was very similar to the ropes from crab pots that are set by fishermen in my study area," says Kot.

Crab pots set on the seafloor are baited and held by a rope leading up to the surface, which is attached to a buoy. Often a series of cages are connected by floating ropes that are thought to entangle whales.

Kot and his team observed and videoed the injured minke feeding on schools of capelin for over 80 minutes.

An analysis of the video showed that the minke, which lunged into the fish schools 50 times, had no problem accelerating into each lunge.

But the whale often breached in a way never before recorded among minkes.

On 18 of the 50 lunges, the whale breached at an angle of 30 to 45 degrees to the surface, feeding on its right side only, as can be seen in the picture above.

It would then rotate in the air to land upright on its chin. The researchers never saw the whale breach from its left side, or spin in mid air to land on its left. The whale was also unable to distend its feeding pouch as far as other healthy whales.

"The injury seemed to affect the expansion of the ventral pouch and I noticed a unique lunge-feeding behaviour that has not been previously described in the scientific literature," says Kot.

Despite often seeing the same whales repeatedly in his study area in the Gulf of St Lawrence, Kot has not seen the injured minke whale again, so he doesn't know what long-term impact the wounds had.

"We really don't know what happened to it. Perhaps the injured animal left the area and survived or perished some time in the future."

However, the sighting of the minke whale is valuable as it's "one of the first to show the effect of an entanglement-like injury in a live animal," says Kot.

By some estimates, fishing gear poses the greatest threat to whales.

Yet little is actually known about the impact fishing that gear has on the survival of these ocean giants.

In particular, almost nothing is known about the non-lethal impact caused by entanglement injuries.

"Cetacean entanglements involving various kinds of fishing gear have been a global concern for many years," says Kot.

"However, with the steadily increasing demand for food, fishing pressure in the world's oceans has increased the amount of gear that whales can potentially encounter."

And many coastal fisheries operate exactly where the smaller and more vulnerable species of whale and dolphin range.

"Some of the largest whales, such as blue or fin, can sometimes free themselves from entanglements due to their size and strength," Kot explains. "Smaller whales like minke likely don't have this ability."

And most small whales that do get trapped probably drown and sink, never to be found by anyone, including the fishermen who own the net, he says.