Are southern elephant seals attracted by the bioluminescence of lantern fishes in the deep dark of thesouthern Ocean?

Bioluminescence, the emission of visible light by living organism, is mostly found in the deep ocean where it is used to avoid or help predation as well as communication between conspecifics. This work is based on the hypothesis that bioluminescence could also be used by predators, here the southern elephant seals (SES), to locate their prey. It has been shown that SES are endowed with a vision adapted to low light intensity with a peak sensitivity at 479 nm, matching not only the wavelength of natural light at depth but also the bioluminescent spectrum of most mesopelagic organisms. Lantern fishes represent the biggest biomass in the southern ocean and are known to be SES’s main prey. In this work, we aimed to reveal that Prey Catch Attempts (PCA) might be related to bioluminescent events. By stimulating the bioluminescence of lantern fishes trawled during Mycto 3D expedition (MD197) and by analysing diving behaviour of three satellite-tracked females equipped with high sampling rate Time-Depth-Light 3D-accelerometers and magnetometers recorders (MK10-X and DDT) we were able (i) to link the number of Prey Catch Attempts (PCA), assessed from the processing of accelerometer data, with the number of detected bioluminescence events; (ii) to assess if SES modified trajectory and performed PCA in relation to bioluminescence events; (iii) to measure bioluminescence characteristics of several lantern fishes species. Results revealed that lantern fishes produced a blue luminescence (450nm) and although PCA could take place in absence of bioluminescence events, we found that PCA was positively related to bioluminescence events which provide strong support that bioluminescence represents a key element in predator-prey interactions