In a paper recently published by the British Journal of Natural History, the relationship between the fierce Antarctic predators - the giant squid and toothfish - are called "Alien vs. Predator". Scientists were able to confirm that these deep-water predators are dangerous for each other, attacking the weak or insufficiently strong individuals.
In general, scientists are limited by very sparse sources in the study of the cold and the dark depths of the ocean, restoring the lifestyle and behavior of its inhabitants using the remains and traces of committed "crimes". For example, giant Mesonychoteuthis hamiltoni squid - the largest of the cephalopod of the Earth - was discovered less than a hundred years ago by the fragments found in the stomach of a sperm whale harpooned by whalers.
Until now, such "circumstantial evidences" remain the main source of information about these shellfishes. They have been caught as a whole just a few times and have never been observed in the wild at a depth of 500 to 2,000 meters by anyone.Giant Antarctic squid on the deck of the Russian "Eurica" research ship. Photo Copy Copy Right Alexander Remeslo
Meanwhile, a giant (sometimes called "colossal") squid is one of the most common predators of mesopelagic and bathypelagic areas of the Southern Ocean. Its weight can reach half a ton, and the size of the mantle reaches 2.5 m. The preys correspond with the predator: it is believed that the Antarctic seas giant squid hunt on other cephalopods (including their own tribesmen) and local fishes, including the Dissostichus mawsoni Antarctic toothfish - exceptionally large commercial percoid whose size can reach up to 2 m.
The giant squid and the Antarctic toothfish are predators that occupy some of the highest levels of the food chain. Strong adults can be caught by the sperm whales, in which stomachs their remains are found, although it is assumed that not reached full power - or simply relaxed - squid or toothfish may be affected by one another. On the other hand, the squids are not fast enough to try to catch up and grab with fishes reaching more than 100 kg: most likely, they prefer "ambush" hunt type, grabbing nearby victim with tentacles studded with powerful hooks.
Because of the exceptional difficulties in studying these deep sea giants, much of their way of life remains unclear, so every work in this topic draws a lot of attention.
"The interest we received in response, turned out to be a big surprise - Alexander Remeslo, one of the authors of a new study, a senior fellow at the Atlantic Research Institute of Fisheries and Oceanography, said in an interview with STRF. - Right now I have accumulated dozens of applications about this article from professionals from different countries".
Researchers spent several fishing seasons onboard the South Korean vessels engaged in fishing in the southern Antarctic seas, and analyzed more than 8 thousand toothfishes caught. Scientists have noted the wounds left by suction cups and hooks of giant squid tentacles at 71 fishes, and fragments of mollusks themselves in the stomachs of 57 fishes. According to the researchers, the number of toothfishes damaged by squids in catches ranged from 0.15% to 2.27%.
The highest frequency of attacks was recorded in the Davis Sea and the Commonwealth Sea near the east coast of the Antarctic, while they are much less likely to have occurred in the Ross Sea located much far to the west. "In this case, it is almost impossible to determine the depth at which the attacks took place - Alexander Remeslo adds. - Most likely, squids attack a fish on hook while lifting the layers in the water column as rotten part of toothfishes flesh as a rule does not exceed 3.1 kg".
Even more difficult to say how fragments of squid tentacles of very impressive size got in the stomachs of some of toothfishes where they are found - it is unlikely that the fishes might attack the victims several times larger than themselves. Scientists suggest that toothfishes attack only greatly weakened M. hamiltoni squids, eating meat of dying and dead animals, not disdaining the remnants of the feast of larger predators.