Recording sperm whales gives suggestions for sound research in fish and fishing strategies

For decades, scientists have been fascinated by the diverse sounds emitted by sperm whales, in part because of the popular theory in the scientific world that these sounds contain information about jacks. fish ruler. But until now, there has been virtually no proof that these sounds can reveal information about the physical characteristics of this great marine animal. Now, researchers at Scripps Institution of Oceanography at the University of California in San Diego have solved some of the secrets surrounding the sounds of sperm whales.

In an article in the Journal of the Acoustical Society of America in May, Delphine Mathias and Aaron Thode of Scripps Oceanographic Institute first described a direct comparison between the sounds of sperm whales and those fish head characteristics, including head size and internal organ structure.

The study offers suggestions for a new approach to sound-based biological investigations, and possibly an accurate investigation of the number of individuals of this species.

The origin of this study dates back many years in Alaska, after the sperm whale developed the ability to steal the black cod from the fishing line, offshore fishing equipment has a main line dropping along the sea, and a shorter string to tie the hook with bait. Black cod fishermen began to realize that their fishing boat had attracted every flock of sperm whales - who just went to feed alone - to their fishing lines.

To help fishermen and scientists better understand the problem, in 2004, the Scripps Institute's research teams placed tape recorders along the coast of Sitka, Alaska. This is part of the SEASWAP (Southeast Alaska Sperm Whale Avoidance Project) project. The results helped identify the sounds that attracted this fish to the fishing vessels. Encouraged, in 2006, the research team installed additional cameras on fishing gear, and from there obtained unexpected results.

Photo taken from a video filming a sperm whale at the coast of Sitka, Alaska on May 31, 2006 (Photo: Scripps Oceanographic Research Institute, University of California at San Diego)

The video was recorded at a depth of 100 meters (328 feet) that gave fishermen a thorough answer on how to steal the sperm whales - they shook one end of the string to wobble the black cod and make it falls off the other end of the rope, like when we shake the apples from the tree - and at the same time gives scientists the opportunity to pair the sounds with the fish's physical characteristics in the video. Sperm fish often dive to dark waters at depths of 300 to 2000 meters (ie 984 to 6,500 feet) to catch prey, so most of us cannot record their activities. The fact that these fish emit a sword feed in such shallow water around fishing boats is a special feature of the footage captured in Alaska.

According to Thode, a research associate with Scripps Institute's Marine Physics Laboratory, sounds from sperm whales are emitted more and more faster as they get closer to the target, and this is one of the sounds The deepest, biggest bar in the world of animals.

'This sound may be louder than a cannon,' said Thode. 'But before this video was shot, scientists never directly measured the size of the fish, as well as the sound it emitted when feeding.'

Alaska video allowed Mathias and Thode to not only match the size of fish heads with negative signals, but also deduce the size of the fish oil secretion, a white substance with a waxy texture that was once used. used as candles and ointments, as well as parts called 'wax tissue' inside the fish head. This wax tissue is a large part believed to play a role in transmitting sound from fish heads.

Thode said this study could be the first step to using the sounds collected to calculate the number of sperm whales in addition to the naked eye count. Currently it is difficult to find the relationship between the amount of recorded sound and the actual number of fish. The ability to separate sounds of each sperm whale is a basic step to solve the problem.

'It is interesting that you identify each individual by the sound it produces, and this is what people have been longing for,' said Thode. 'Humans only need to use a negative character to identify each person when talking on the phone, but this is many times more difficult when applied to animals.'

Thode said the recording also helped fishermen deal with the situation that sperm whales attacked their fishing lines. Besides economic losses, this also poses a risk for both humans and fish in case the sperm whale is caught in the fishing line. Thode said the recording encouraged the National Fisheries Service to begin installing sound recorders in black cod surveys on the Alaskan coast to assess the level of sperm whale issues.

The research is supported by the National Geographic Association and the North Pacific Research Commission.

References:
Delphine Mathias, Aaron Thode, Jan Straley, and Kendall Folkert.Relationship between sperm whale (Physeter macrocephalus) click structure and size derived from videocamera images of a depredating whale (sperm whale prey acquisition).The Journal of the Acoustical Society of America, 2009;125 (5): 3444 DOI: 10.1121 / 1.3097758