During the winter fishing for herring in the fjords of Troms, there are often many whales around the fishing vessels. Photographer: A. Rikardsen/UiT

Scientists have found sounds that keep killer whales away from fishing boats

NORWAY
Thursday, May 23, 2024, 01:50 (GMT + 9)

But the humpback whales are worse.

"The sound signals that we have used worked very well on killer whales, but not so well on humpback whales. The orcas disappeared almost immediately from the area around the fishing boats whenever the sounds were played".

That's what marine researcher Maria Tenningen says.

More agile killer whales

During the winter fishing for herring in the fjords of Troms, the researchers tested various sound signals.

"Then there are huge numbers of whales around the fishing boats. So there is always a risk that they will be caught in the bill", says Tenningen.

"And it is important to avoid this for several reasons. If the whales are caught, there will be problems for both them and the fishermen. The whales can be injured or, in the worst case, drown, and the fishermen can lose their catch and have their gear destroyed", she adds.

It is the humpback whales that are the biggest problem for the fishermen.

"They get stuck in the net more often and are also more difficult to get out because of their size, the long pectoral fins and the wart-like bumps on the body. Killer whales don't end up in the news as often", says the marine researcher.

The final report is ready

The project "Mapping and testing methods to reduce interactions between fisheries and whales", which has been led by Tenningen, has now been completed.

Since the project began in 2021, the researchers have been trying to find the right sound signals that can keep killer whales and humpback whales away from fishing boats and whales.

The results have recently been published in a final report.

The humpback whales "dilted" after the killer whales

When Tenningen and his research colleagues tested different sound signals on the humpback whales, they got little response. Although the signals appeared to induce a short-term startle response, none of them managed to keep the whales away from the fishing boats.

Audio unit (a), underwater speaker (b) and battery (c) used in the exposure experiment. (Figure from Tenningen et al., 2023)

But when there were also killer whales in the area, the humpback whales behaved differently.

"Then the humpback whales reacted. It seems they were following the killer whales. But when the humpback whales were alone, they did not react to the sound signals," says Tenningen.

In the fisheries experiments, however, the researchers have only used sound signals with a frequency that is best suited for killer whales. The humpback whales hear lower frequencies, but they are not reproduced well enough without a more powerful speaker than was available when the experiments were carried out.

Experimental setup. Sound exposure and recording of whale blow was from a small boat positioned next to the fishing boat at a 90 degree angle from the bow of the fishing boat. The area where the registrations were made was divided into 4 zones (A, B, C and D). (Figure from Langstein, 2023)

Short and quick sounds

The sounds that worked on the killer whales can also be heard by humans, and were developed by researchers at the University of St. Andrews in Scotland.

"The sounds that were tested are based on the best available knowledge about the hearing of killer whales and humpback whales. The signals are very short, 200 milliseconds, and then they quickly increase in strength", says Tenningen.

The rapid rise in the strength of the sound is key, because it should produce an unconscious startle response that the animals cannot get used to over time. To further avoid that the animals can predict when the sounds will come, the sound signals were also played at random intervals and frequencies.

"The idea is that when the signals come quickly and are short, it creates an unconscious flight reaction", explains the marine scientist.

Small boat with the Institute of Marine Research written on the side on the sea with snow-capped mountains and orange sky in the background. One person in the wheelhouse, and two people on deck. One of these stands in the bow and lowers an apparatus down towards the sea.

Different sound signals were tested during the winter fishing for herring in the fjords in Troms. (Photo: Audun Rikardsen / Institute of Marine Research)

Counted number of whale blows

When the researchers tested the sound signals in the northern Norwegian fjords, they simply used a speaker that they lowered into the water. They did this either from an ordinary fishing boat or from a smaller boat next to it.

The researchers counted the number of whale blows around the fishing boat in a given time period before the sound was played, while the sound was being played and after the playback had finished. In this way, they could see changes in the number of whales present between the three periods.

Expected reduction in orca blow (%) in the various observation zones during sound exposure compared to before exposure based on the Generalized Linear Mixed Model (GLMM). Zones A and C are the two zones closest to the speaker (0-50m), while zones B and D are further away (50-100m). The circles are expected values ​​and the bars 95% confidence intervals (Figure from Langstein, 2023).

Must find the sounds that work on the humpback whales

The project, which has been a collaboration between the Institute of Marine Research, the University of St. Andrews and UiT Norway's Arctic University, is now being extended for a further two years.

The researchers will then, among other things, find more practical ways in which the fishermen can use this sound method, so that they release large speakers with lots of wires hanging down in the water from the boats.

- And then we will try to find the right sound signals that will keep the humpback whales away from the fishing boats. Even when they are alone - without help from the killer whales, says Tenningen.

Author: Anders Jakobsen / Institute of Marine Research (Havforskningsinstituttet) | Translated from original in Norwegian

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