According to a new study by the Technical University of Catalonia in Barcelona, squid and other cephalopods are affected by sound waves similarly to marine mammals such as whales and dolphins. Although it has been hypothesized to be the case, it had never before been observed in cephalopods until this study was done.
The most important outcome of this study so far is that it provides an explanation for what caused the deaths of giant squid in the early 2000’s in Spain’s Asturias province. Several dead giant squid were observed in this province shortly after ships had transmitted low-frequency sound pulses. Some of these ships were involved in oil and gas prospecting.
Scientists who had studied the dead squid at the time observed that their muscles were bruised and their mantles were reduced to pulp. Lesions also affected their statocysts, organs which are located behind the eyes of giant squid and help to maintain their balance. However, scientists could not conclusively tie these deaths to sound waves at the time and needed time to research the possibility.
The experiment some of them eventually conducted in Catalonia involved 87 individual cephalopods. These individuals came from two species of squid, one species of octopus, and one species of cuttlefish. They were exposed to sound for two hours with frequencies ranging from 50 to 400 Hertz and intensities between 157 and 175 decibels. These frequencies were chosen because they are commonly heard in noise-producing activities such as military sonar tests or tests to detect oil and natural gas beneath the seabed.
Some of the cephalopods were killed immediately after listening to these frequencies, but others were allowed to live longer, up to 96 hours. Scientists then examined their tissues to see the extent of the damage. These cephalopods were primarily impaired through losing the use of certain hairlike structures in stratocyst cells that help them balance in water. They became crippled through these structures, and those that were allowed to live longer developed visible holes in their tissues. In their final minutes, it is said that they “moved a little bit, but they were not swimming, eating, or mating” according to Michel André, a marine bioacoustician at the Technical University of Catalonia.
There was also a control group of about a hundred cephalopods who were raised in the same aquariums under the same conditions as those who were tested, but were not subjected to the sound waves. This group remained healthy and did not show any of the symptoms mentioned above. Both groups of cephalopods were healthy before the testing occurred.
Although these cephalopods were smaller than giant squid, experts say that these results were also applicable to them. However, the damage to the giant squid was far more extensive than to the cephalopods. This was because the giant squid were exposed to the sound waves for a much larger period of time, at a greater intensity, and from multiple sources.
The giant squid could have died in one of two ways: either from the direct impact of the sound waves or by getting disoriented from an impaired sensory organ. If a giant squid got disoriented, it could surface, not knowing that it could not handle the rapid change in temperature and pressure.
The idea that the squid were disoriented is supported by studies showing that when whales are exposed to sonar, they suffer symptoms similar to what divers call “the bends.” These symptoms occur when a diver is surfacing too rapidly. The extreme pressure change makes nitrogen bubbles form in the blood and vital organs. If not treated properly, it can cause fatal damage to the brain and lungs.
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