Deep-Sea Fish Avoid The Dead

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Coryphaenoides armatus arrive to feed on bait (mackerel) set by ROBIO. Photo from here

A recent study by Barry and Drazen (open access)notes that some deep-sea fishes avoid the odor of dead conspecifics. Coryphaenoides armatus, the Pacific grenadier, is a prominent scavenger and typically one of the first fish to arrive at a food fall of a carcass. However, in caging experiments to test the effects of ocean acidification on seafloor organisms, cages where C. armatus died potentially due to cage-related stress, predation, or exposure to acidic waters, did not attract C. armatus. Figure 6 (below) from the paper demonstrates this clearly showing the number of individuals that visit per time unit. At time 0 hours, C. armatus dies in the cage. For over a week (200 hours) there are no visits of C. armatus despite the appearance of other scanvengers (the octopus Bentoctopus sp. and the snubnose eelpout Pachycara bulbiceps).

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Why did grenadiers avoid the cage? The authors suggest four possible hypotheses: 1) sensitivity to the acidification experiment, 2) inability to detect a weak odor plume or the odor was unappealing to scavengers, 3) quick departure from inaccessible a carcass (the dead grenadier was caged), and potentially the most interesting 4) avoidance of dead or dying individuals of the same species. 1 is unlikely as grenadiers were present at the initiation of the experiment. 2 is unlikely as other scavengers arrived at the cage. 3 is also unlikely because grenadiers were present at the cage when the original bait placed. Thus the questions is why do grenadiers avoid the dead and dying? One explanation is that the behaviour represents an adaptation to avoid potentially dangerous situations such as predation events, physiological taxing habitats, or diseased individuals.

Dr. M (1796 Posts)

Craig McClain is the Executive Director of the Lousiana University Marine Consortium. He has conducted deep-sea research for 20 years and published over 50 papers in the area. He has participated in and led dozens of oceanographic expeditions taken him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses on how energy drives the biology of marine invertebrates from individuals to ecosystems, specifically, seeking to uncover how organisms are adapted to different levels of carbon availability, i.e. food, and how this determines the kinds and number of species in different parts of the oceans. Additionally, Craig is obsessed with the size of things. Sometimes this translated into actually scientific research. Craig’s research has been featured on National Public Radio, Discovery Channel, Fox News, National Geographic and ABC News. In addition to his scientific research, Craig also advocates the need for scientists to connect with the public and is the founder and chief editor of the acclaimed Deep-Sea News (http://deepseanews.com/), a popular ocean-themed blog that has won numerous awards. His writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web.