Humpbacks cannot hear you - a message for sailors

The humpback cannot hear you
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Research round the world suggests that the number of whales in the world is increasing, and it certainly seems true on the Australian east coast. Now new research in Southeast Alaska suggests the number of collisions between boats and whales is on the rise, perhaps caused by the inability of humpback whales to hear through echo-location or sonar.

The growing humpback population in the region might explain the increase. These collisions are dangerous not only for whales, but can also be a frightening experience for smaller boats plying the waters of Alaska.

The owner of a 50-foot yacht, Loreley, tells the story of their collision with a whale. The boat was moving at about eight knots down the middle of Chatham Strait in Alaska in June this year when it stopped very suddenly.

'Everything was thrown forward,' said Viktor Grabner, 'All drawers, forward-facing opened up. We came to a halt, seemingly within a boat length. We just didn’t know what to think. I immediately looked at the depth sounder thinking we hit a reef or a rock, but we were in Chatham Strait and the depths were greater than 1000 ft.'

He rushed to the engine room to check for leaks. No visible damage. Up in the wheelhouse, his wife Diane searched for the cause of their abrupt stop. A humpback whale surfaced and flipped a bloody tail at the boat.

'It didn’t even occur to me that we could have hit a whale.'

These strikes can be dangerous for small boats, according to National Park Service wildlife biologist Janet Neilson.

'In some cases that can be a serious collision for the whale as well, but in many cases it’s more serious for the vessel. A whale can do a lot of damage to a smaller vessel and it’s becoming a public safety issue. The operators of smaller vessels that are colliding with whales are in many cases getting injured by those collisions.'

Neilson says strikes often occur because humpback whales cannot hear fast-moving vessels.

'A lot of people are under the perception that humpback whales and other baleen whales can detect vessels on the water through echo-location or sonar, but baleen whales do not have the ability to echo-locate like toothed whales. So they’re often relying on passive hearing and they do have a difficult time detecting fast-moving vessels because they did not evolve in an environment with fast-moving underwater sound. So it’s difficult for them to locate the sound. So the best thing to do is slow down and keep a sharp lookout.'

Neilson and NFMS’ Jensen are co-authoring a study on whale strikes in Alaska, along with another Park Service biologist and a researcher at UAS. The study shows that since 1978, one hundred and nine whale strikes have been reported, with more in recent years. However, Neilson says only a fraction of collisions are reported, complicating the question of whether they are actually on the rise.

'But we would expect to see an increase in the number of strikes because the humpback whale population is on the rise. It’s estimated to be increasing about 5% per year in Southeast Alaska. So with more and more whales around, there’s just more chances of them getting hit.'

An estimated 3,000-5,000 humpback whales feed in Southeast Alaskan waters during the summer months.

Grabner, who hit the whale in Chatham Strait, says he keeps a closer eye on whales near his boat than he used to.

'We saw one yesterday and it causes a little minor alarm aboard when we see one because we are now extra cautious, now having learned that you can run into them. Or they run into you, depending… But any way, it kind of changed our attitude towards taking a whale sighting much more seriously than we have in the past.'