Deep-sea fish characterization on Necker Island, Papahānaumokuākea Marine National Monument

Some seamounts harbor a high abundance and diversity of fishes. However, evidence is emerging that within any given seamount, these attributes may vary strongly depending on variability in the physical, chemical or geological... [ view full abstract ]

Some seamounts harbor a high abundance and diversity of fishes. However, evidence is emerging that within any given seamount, these attributes may vary strongly depending on variability in the physical, chemical or geological conditions. Necker Island, the second smallest island in the Papahānaumokuākea Marine National Monument (PMNM), includes a diversity of deep-sea habitats. Unlike seamounts further west in the PMNM, it has not been subject to commercial trawl fisheries. The relatively pristine nature of this site allows for baseline studies of deep-sea fish communities that can improve our understanding of the distributions of fishes on seamounts as well as inform management of sites throughout the Hawaiian Archipelago. Using 52,098 AUV photos we identified 18,515 fishes from three sides of Necker Island at depths of 200-700 m. The dominant fish orders identified were Stomiiformes, Aulopiformes, Gadiformes, Myctophiformes and Perciformes. Species richness showed significant differences among depths, sides of the seamount, and their interaction. Relative abundance was significantly different among sides, whereas Shannon diversity and Simpson dominance showed differences among depths and their interaction with sides. The highest richness was found at 500 m, in which diversity was also very high with low dominance. The highest values of dominance were observed at 250 and 700 m. Community structure was different among depths, sides, and their interaction, with a variation along a depth gradient. At deeper depths pelagic fishes were dominant, whereas shallower depths were dominated by benthic fishes. Based on DISTLM, fish community structure was most strongly correlated with depth and POC.