It seems that mesopelagic fish are smarter than we thought, and use the same avoidance reactions that protect them from their predators to give wide berth to the sampling nets used to estimate their abundance. Professor Stein Kaartvedt worked with colleagues from the University of Bergen, to monitor this avoidance behavior using echo sounders in one of Norway’s deep fjords. In a paper published as a feature article in the journal Marine Ecology Progress Series on June 7, first author Prof. Kaartvedt describes how the threat of a trawling net caused the fish to scatter in its path, leaving a void that persisted for several hours in the calm waters. This mirrors the flight behavior of smaller fish when they encounter predators seeking their next meal.
In both cases, the smaller fish seem to relax after the encounter, but their apparently lethargic pose belies their readiness to flee if threatened. The particular fish under observation, Benthosema glaciale, is the most common myctophid (lanternfish) in the northern Atlantic, and lanternfish are the most common mesopelagic fish worldwide. The study suggests that the population of mesopelagic fish in the world’s oceans could have been underestimated by at least 10 times because of their wily behavior, which could have huge significance.
No one is sure how the lanternfish detect predators, but it is thought to involve a combination of sensory stimuli; the fish’s large eyes are very light sensitive and can detect the bioluminescent flashes that a trawler moving through water would create, at distances of tens of meters.
2 comments
It appears the article link is incorrect.
The link has been corrected. Thanks for notifying us.