Variation in locomotion behaviour in northern cutthroat eel (Synaphobranchus kaupi) on the Bay of Biscay continental slope

Based on the analysis of video sequences recorded during four dives with a manned submersible in the Bay of Biscay, NE Atlantic, evidence is provided that the northern cutthroat eel Synaphobranchus kaupi shows marked variations in abundance and in the adoption of three locomotion behaviours—forward movement, station holding, and drifting—among six ecologically different habitats. Furthermore, significant variations in association with the bottom and disturbance responses to the submersible were found. Two swimming velocity measures taken from eels during forward movement were significantly correlated with both depth and temperature. The behavioural variations observed partly occurred also between adjacent habitats that were crossed during the same dive. These results and additional observations of instantaneous fluctuations in hydrological conditions suggest that these deep-sea eels are able to adjust to ecological variability at small spatial and temporal scales in a flexible and adaptive way.