Behaviour and patterns of habitat utilisation by deep-sea fish. Analysis of observations recorded by the submersible Nautilus in "98" in the Bay of Biscay, NE Atlantic

Abstract

Analysis of video recordings performed by the submersible “Nautile” in the Bay of Biscay, NE Atlantic indicated that demersal fish species are associated to different types of deep-sea habitats. Four different dive transects were analysed with respect to environmental characteristics. A total of 19 fish groups were ordinated by means of canonical correspondence analysis, and the investigation was performed at the individual fish level. Microhabitat fauna was dominated by a diversity of suspension feeders indicating different gradients of bottom hydrology, particularly vertical and horizontal current flow. Physical, geological and biological factors revealed different strategies of habitat selection in fish. The most represented species, the orange roughy (Hoplostethus atlanticus) showed a clear association with complex bottoms, including coral reefs. Others, such as Coryphaenoides rupestris and Synaphobranchus kaupi, showed higher flexibility of adjustment to changing environments. These traits can be utilised in the study of the environmental impact of deep-sea fishing. Based on the same dives, the locomotory behaviour of 13 fish species was studied with basis on a qualitative analysis of selected individuals. The main swimming modes used in shallow waters were also detected in the demersal environment. Clear differences in locomotory behaviour were found among fish species, reflecting both convergence and diversity of strategies of utilization of the demersal niche space.