How To Stop Whales Getting Entangled In Our Nets

North Atlantic Right Whales are one of the most endangered whale species, but we may not have seen the end of them. Credit: Stephen Meese/Shutterstock.

Most of the world no longer hunts whales, and instead is trying to save them. Nevertheless, we often kill them accidently. Fortunately, new research shows an easy way to cut a major cause of death for one of the most endangered cetacean species.

Even without hunting, whales are killed in collisions with boats and by becoming entangled in nets and fishing gear. There are also concerns that the underwater noises we make are interfering with their ability to find each other over large distances

The North Atlantic Right Whale (Eubalaena glacialis) is so endangered that Amy Knowlton of the New England Aquarium is conducting a program to monitor and map the family tree of every surviving member of the species. An extraordinary 50,000 sightings have been cataloged, and samples taken from more than 75% of the members of the species.

All of these observations have revealed that entanglements are “The second most common cause of right whale death.”

However, Knowlton brings good news. In Conservation Biology she reports that the strength of rope makes a big difference to whether whales stay entangled. “Our results suggest that broad adoption of ropes with breaking strengths of 1700 lbs [773 kilograms] or less could reduce the number of life-threatening entanglements for large whales by at least 72%, and still be strong enough to withstand the routine forces involved in many fishing operations,” Knowlton and her co-authors write.

Knowlton and her colleagues reached this conclusion by examining 132 ropes retrieved from 30 entangled whales and measuring their strengths. The ropes averaged 1187 kilograms (2616 pounds) and were on average 26% weaker than at manufacture, suggesting that time in the water had affected their strength. However, this apparently was still too much for the whales.

Nevertheless, there was a difference in rope strength by species and age. “Right and humpback whales were found in ropes with significantly stronger breaking strengths at manufacture than minke whales,” the authors report, adding, “Adult right whales were found in stronger ropes than juvenile right whales.”

In other words larger adult whales were not caught in weaker ropes, not because those ropes are not being used, but because they were able to break them. Meanwhile juveniles and smaller species lacked the strength to break even the weaker ropes, and were killed by them.

Knowlton's prescription might do little for the smaller species, or even for young right whales, but it could still be enough to save the most endangered species, with the authors noting, “A reduction of this magnitude would achieve nearly all of the mitigation legally required for US stocks of North Atlantic right and humpback whales.”

One of the projects the New England Aquarium is running is to design fishing gear that will reduce the danger to whales and other non-target species.

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