Scientists in Norway have identified sounds that discourage killer whales from approaching fishing gears, but keeping humpbacks away is proving more of a challenge.
‘The sound signals 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 vessels whenever the sounds were played,’ said marine researcher Maria Tenningen, who led the research team during the winter fishery in the Troms fjords to test a variety of sound signals.
‘There are huge numbers of whales around the fishing boats. So there is always a risk that they will be caught,’ she said.
‘It’s 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 commented that humpback whales present the greatest problems for fishermen.
‘They get caught inside 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 nets as often.’
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, and the results have been made available in a report.
The researchers tested different sound signals on the humpback whales, and although the signals appeared to induce a short-term response, none of these managed to keep the whales away from the fishing vessels. 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,’ Maria Tenningen said, adding that the researchers used sound signals with a frequency that is best suited for killer whales. Humpback whales tend to hear lower frequencies, but these would require a more powerful speaker than was available during the trials.
‘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,’ Maria Tenningen said.
The rapid increase in the strength of the sound is key, designed to produce an unconscious flight response that the animals do become accustomed to. These were also played at random imtervals, so as to prevent the animals being able to predict them.
The project, 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. This will include examining practical ways in which fishermen can use this sound method.
‘Then we will try to find the right sound signals that will keep the humpback whales away from the fishing vessels. Even when they are alone – without help from the killer whales,’ researcher Maria Tenningen said.
