Washington, May 23 (Inditop) Sperm whales have been caught on camera stealing cod off fishing gear.
The unique video shot on CCTV cameras shows sperm whales’ ability to steal black cod off longlines of deep-sea fishing gear that features a main fishing line draped across the ocean and fastened with shorter lines bearing baited hooks.
Frustrated black cod fishermen began to realise that their longline fishing boats were attracting groups of whales, which typically forage alone, to their longlines, somehow alerting the animals like a dinner bell.
To help fishermen and scientists better understand this behaviour, Scripps Institution of Oceanography researchers deployed acoustic recorders on longlines in 2004 off Sitka, Alaska, as part of the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP).
The results helped identify the sounds that attract whales to the fishing vessels. Encouraged, researchers added video cameras to the fishing gear in 2006, which led to some unexpected results.
The resulting video, recorded using ambient light at 100 metres depth, not only successfully gave the fishermen a clear idea of how the thieving whales were stealing the fish.
They pluck the line at one end to jar the black cod free at the other end, somewhat like shaking apples from a tree-but it gave scientists a chance to match the animal’s acoustics with video depictions of its physical features.
Sperm whales typically dive to dark depths spanning 300 to 2,000 meters to catch prey, making it virtually impossible to capture such activity on video.
The fact that the animals produce foraging sounds at such shallow depths around fishing vessels is the main reason the Alaska footage is so unique.
The clicks emitted by the whales are produced more rapidly as they approach their targets of interest and are among the loudest and most intense sounds produced by any animal, according to Thode, associate scientist with Scripps Marine Physical Laboratory.
“The sounds can be louder than a firecracker,” said Thode. “But until this video recording was made, scientists had not been able to get a direct measurement of the size of the animal and the foraging sounds at the same time.”
The study was published in the May issue of the Journal of the Acoustical Society of America.
