By Andrea Barthelemy
The sound of the cutters approaching to gather fish caught in pre-laid nets has long functioned as a kind of dinner gong for the sperm whales that populate the Gulf of Alaska. Sperm whales, which are an endangered species and protected under the Marine Mammal Protection Act, are in many ways still a mystery to humans. The world’s largest toothed predators can grow to more than 20 metres long and can easily dive to 1,500 metres below sea level.
The resourceful creatures have learned to follow the sound of the boats, flocking to the surface and swimming in their wake before stealing the fish right from under the noses of the fishermen. They then proceed to gorge themselves on the fish that have been caught by the long fishing lines, which have up to 4,000 hooks. Researchers and fishermen are now working together to find a way of addressing the problem.
The unusual behaviour of the whales was first observed more than two decades ago, when the rules regarding fishing for pollock in the Gulf of Alaska were changed - from 10 days a year, with no limits on how many fish could be caught, to eight months, but with quotas. The whales were quick to catch on to the fact that a buffet was available to them nearly three-quarters of the year along the fishing lines, which lie approximately 700 to 1,100 metres below the surface.
“The most experienced whales found they could bite and shake their leash - the same way you shake apples off the tree,” said Aaron Thode, a marine mammal expert for the Scripps Institute of Oceanography in California, in an interview at the time.
He had observed the animals with underwater cameras. Since the pollock fell quite easily from the line due to their soft mouths, the whales were able to avoid injuring themselves. However, there was still a risk that they could be injured by the lines or the boats.
According to the North Pacific Fisheries Association, the whales’ behaviour was leading to losses of more than 1,000 dollars a day per boat. The fishermen were regularly losing a quarter - and sometimes as much as 100 per cent - of their catch, the association says.
That’s why, since 2003, local fishermen have been working with environmental researchers from the National Oceanic and Atmospheric Administration (NOAA) on a project known as SEASWAP.
Whales can hold their breath underwater for up to 100 minutes and often re-emerge huge distances away. To this day, the purpose of the massive spermaceti organ in their bulbous heads remains unclear. Does it simply serve as a battering ram? Or is it used for echolocation? The first thing the researchers wanted to establish was what exactly was attracting the whales. “It was not just any part of the equipment, it was the way the fishermen drove the boats,” said Thode.
They did a dummy run with no catch, where a boat accelerated and then stopped, shaking up the water and generating air bubbles as it would during a catch. “In less than 10 minutes, we had 12-metre whales around our boat,” said Thode. In calm conditions, the animals can hear the boats from up to 25 kilometres away.
Plan A - to lure the sperm whales away from the fishing boats with an acoustic “food gong buoy” - didn’t work out. The animals quickly caught on that there was no food at the buoy and stayed away.
Plan B - to fish in whale-free waters - has been more successful. The researchers have tagged some of the animals with tracking devices, and a web app now shows where they are swimming. The fishermen can then choose to lay their lines elsewhere.
In addition, the fishermen report individual whale sightings to a central office, which passes on the information to everyone. In 2017, Alaska’s fisheries council also approved a new method for catching pollock in baskets, much like lobsters - a method that is much safer for whales. However, the method is too expensive for many fishermen.
Whale avoidance therefore remains the best strategy for outwitting the clever creatures. Nevertheless, 5 percent of the annual catch still ends up in their huge stomachs.– DPA
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