Fine Scale Movement of the Lustrous Pomfret (Eumegistus Illustris) at Cross Seamount

Abstract

Aggregations of fish are believed to be supported by trophic subsidizing mechanisms resulting from bio-physical interactions at seamounts that lead to increased micronekton abundances or concentrations. Tracking individual fish behavior is one way to prove this is occurring however until recently tagging studies have not been conducted for deep seamount fish species. Using advanced acoustic and archival tags we successfully tagged Eumegistus illustris individuals inhabiting an isolated Hawaiian seamount at depths down to ~600m. We tracked 26 individuals and compared their movements to existing micronekton surveys at Cross Seamount in the context of feeding ecology and accepted trophic subsidizing mechanisms and estimated residence time. Fish displayed strong diel vertical migration behavior, swimming into the water column at night at depths consistent with feeding on mesopelagic boundary community micronekton and became primarily benthic associated around dawn as the shallow scattering layer compressed along the summit of the seamount. Depth distributions varied between individuals. One individual with an archival tag left the seamount after being tagged and remained away for 90 days suggesting movement between isolated habitats is possible. Fish had a strong association with the seamount and were present 97% of the days they were tracked, on average. Average residence time was 103 days (SD = 162) but this was confounded by indications of high post release mortality.