Trophic Ecology and Mercury Sources for Hawaiian Bottomfish

Jacks and snappers are some of the most valuable bottomfishes in Hawaii.  Despite their importance, little is known about their trophic ecology or where the mercury (Hg) that ultimately resides in their tissue originates.  We investigated these topics by analyzing tissue samples for trace Hg content, nitrogen, carbon and amino acid specific isotopes in five species of bottomfish distributed across different depths from the Northwestern Hawaiian Islands (NWHI) and the Main Hawaiian Islands (MHI).  Species had significantly different sources of nitrogen and carbon, particularly shallow water species, which had isotopic values suggesting benthic sources.  High trophic level snappers that foraged in deep water, benthic environments generally had higher Hg levels. These results suggested that benthic Hg methylation is an important source of Hg for shallow benthic feeders, while deepwater sources of methylmercury may be important for those with food derived from the pelagic environment.  Models and Hg levels did not differ between the MHI and NWHI suggesting freshwater sources of Hg methylation were not a major source of Hg in snappers.  Understanding Hg sources and more detailed information on feeding ecology will improve our knowledge of trophic pathways and dietary partitioning within the bottomfish assemblage in Hawaii.