Whales are attracted to fishing boats in search of easy meals but sometimes get caught in fishing nets. Sounds that whales dislike may be the solution for both whales and fishermen.
By: Ellen Kathrine Bludd // UiT The Arctic University of Norway and Stine Hommedal // Institute of Marine Research
There are around 10,000 humpback whales and 15,000 killer whales in the Northeast Atlantic – and they are hungry. In Norwegian waters, these whales typically eat herring, mackerel, and capelin, which are also commercially fished. Norwegian fishermen catch about 1 million tonnes of these fish species each year.
Killer whales and humpbacks are attracted to the fishing boats, both in open waters and in some fjords, for easy food. But this means trouble for whales that inadvertently get tangled in fishing gear.
Fishing boat = Fast food
Researchers from the Institute of Marine Research, UiT The Arctic University of Norway, and the University of St Andrews in Scotland are working together with the fishing industry to find a way to keep the whales away from the herring fishery.
“Norwegian fishermen mainly use purse seines, where fish schools are caught and collected close to the ship’s side before the fish are pumped on board.”
Maria Tenningen, Institute of Marine Research.
Part of the fish school quickly ends up outside the net, either because it was not caught or because it was pushed out again. This is an easy catch for a whale. “The whale saves energy by avoiding doing the job of gathering the fish,” says Tenningen.
Bad for both whales and fishermen
On average, seven humpback whales and eleven killer whales are caught in Norwegian herring nets each year. Some die, but some whales can be disentangled and survive. However, getting the whale out alive is no easy task.
“If the fishermen get a whale in their gear, it’s not good for the whale or the fishermen. Often, the fishermen lose their catch and have their fishing gear destroyed, which can be expensive. They also lose valuable fishing time.”
Audun Rikardsen, professor UiT The Arctic University of Norway
Even if the whale survives, it is often injured, and some eventually die. Rikardsen explains that whale entanglement is therefore also an ethical issue. That’s why it is so important that such situations are reduced to a minimum.
“But keeping a hungry 30-tonne humpback whale or a smart 5-tonne killer whale away from a fishing boat is easier said than done,” says Rikardsen.
New trials show that sound may be the solution.
Fewer whales on fishing grounds
To test if sounds could keep whales away, the marine researchers went out during the winter fishing for Norwegian spring spawning herring in the fjords of Kvænangen in Troms County.
“The idea is that whales will steer clear of the boat and the nets if the boat emits a sound that the whales don’t like.”
Maria Tenningen
“We counted whales before, during, and after the fishing boat emitted sound. Each phase lasted five minutes. Together with the fishermen, we investigated this through 18 herring catches,” says Deanna Leonard, a technician at the Institute of Marine Research.
The number of observations of killer whales on the surface was reduced by 85 percent during the playback of the sound signals, compared to before playback.
A sound killer whales don’t like
The marine researchers used a method developed by the Scottish researchers and Genuswave AS to find sounds that killer and humpback whales perceive as unpleasant, but that don’t harm the animals’ hearing.
“We equipped killer and humpback whales with advanced satellite tags that both film and record the sounds of what the whales are doing underwater. The tags are attached with suction cups and measure other important things like depth and acceleration,” says Audun Rikardsen.
The tags fall off after a few hours and give the researchers a unique insight into how the whales react when exposed to the scare sounds.
“Watching the videos is almost like riding on the whales’ backs and becoming part of their herd,” says an enthusiastic Audun Rikardsen.
Whales returned when the noise stopped
Professor Rikardsen emphasises that the sound signals are in no way harmful to the whales and only work within a limited area around the fishing boat.
“When we stopped playing the sounds, the whales returned to the boats within a few minutes,” he says.
The effect of the sound signal decreased quickly with distance. It was clearly lower at 50–100 metres from the sound source than at 0–50 metres.
“This suggests that killer whales are not harmed by the sound signals and are not permanently scared away from the area,” says Maria Tenningen.
The results are more uncertain for humpback whales, who have a lower hearing frequency range than killer whales. Further research could help determine which sounds work best for both whale species, so that in the future, fishing boats can be equipped with systems that help whales – and fishermen – avoid entanglement.