In an ecological key, nature almost always advances with two protagonists: the hunted and the hunter. We call this game of cat and mouse with a mixed ending for each person’s interests predation, and in WorldOfSoftware we have told several stories with wolves, sharks or hyenas, among others. However, no scene resembles the one observed in the North Atlantic. Scientists have captured an impressive and unusual massacre on the high seas.
Unprecedented death. Every year, millions of capelin (anchovy-like) fish migrate to the coast of Norway to spawn (release their eggs), attracting a host of predators along the way. During one of these migrations, MIT scientists witnessed what has been the largest predation activity ever recorded, one where millions of cod attacked a large school of capelins, consuming approximately 10.5 million of these fish in just four hours.
This event, fascinating for different reasons, has been the subject of a study published in Nature that allowed researchers to observe the population dynamics of both species, fundamental activities for the marine ecosystem in the North Atlantic.
The capelin and his role. The capelin, the reluctant protagonist of this story (Mallotus villosus) is a small fish that feeds on plankton and krill in the cold and productive waters of the North Atlantic. The species plays an essential role in the oceanic food chain, similar to that of anchovies in warmer waters.
Although their abundant population has suffered declines in the past, they have a trick that saves their demographics: the large number of eggs they produce allows them to recover quickly compared to other species. However, this abundance also makes them highly vulnerable to predation, especially during that migration to spawning areas in the gravel of the ocean floor, at depths between two and 100 meters.
Science and monitoring. As reported by MIT, the researchers used advanced sonar technology, called Ocean Acoustic Waveguide Remote Sensing (OAWRS), with which they were able to follow the movements of these fish over a wide area in real time. They say that in the early hours of February 27, 2014, the OAWRS revealed how the capelins, initially dispersed, grouped into a gigantic school of 23 million individuals.
This grouping phenomenon allowed scientists to observe the natural behavior of capelins, who manage to coordinate their movements when they reach a critical density.
OAWRS shows how capelin and cod came together and then dispersed in unison
The banks and the predators. As we said, although forming schools allows capelins to save energy and, in some cases, avoid predators, this concentration also makes them a very attractive target.
Thus, as soon as the massive school of capelin formed, a group of cod, one estimated at 2.5 million fish, began the “hunt.” The scientists observed that the density waves moving through both populations appeared synchronized, showing a dynamic interaction between hunters and prey on an unprecedented scale.
Why does it matter? An event as unique as the one recorded is very important. Although this type of mass predation does not pose a direct threat to capelin populations, as their annual migration in the region includes billions of individuals, scientists express some concern about the impact of climate change.
The reason? Apparently, the loss of spawning areas due to rising global temperatures could limit safe spaces for this type of species, which, in turn, could have serious consequences for the entire North Atlantic marine ecosystem in that wheel that It’s nature.
Bonus ball: understanding marine life. The sonar technology used, the OAWRS, is capable of distinguishing between species by their different resonance frequencies, and has allowed scientists to precisely identify the signals of each type of fish.
As Nicholas Makris of MIT explained, fish swim bladders emit bell-like resonances. Thus they deciphered that those of cod are deep, while those of capelins produce high-pitched sounds. This distinction has been key to the detailed study of these massive predation phenomena and opens the door to a better understanding of marine ecology.
Image | POT, Nicholas Makris, et al
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