Quantifying Pelagic Habitat Use by Myctophid Fishes in the Northern Gulf of Mexico

Deep pelagic ecosystems are some of the largest on Earth but are amongst the least understood. As human impacts on the deep oceans continue to increase, there is an urgent need to understand the processes that influence pelagic fauna, particularly in deep waters. One of the most globally-important taxa are the myctophid fishes, which are a ubiquitous component of the deep-pelagic micronekton and play key roles in the vertical and horizontal transfer of energy between ecosystems. In the present study, we analysed quantitative, depth-stratified trawl data to assess the distributions of the dominant myctophid species in relation to physical and chemical environmental variables in the northern Gulf of Mexico (GoM) during summer 2011. The data were collected through the NOAA-supported Offshore Nekton Sampling and Analysis Program. The vertical distributions of the myctophids were strongly correlated with diel cycles relating to their vertical migration behaviours, but correlations with other environmental variables were generally weak, suggesting limited horizontal structure across the northern GoM. These results suggest that other processes such as migration, random dispersal, population growth or interactions between species may be more important in structuring myctophid communities at this spatial scale than physical or chemical changes in their environments.