Trophic Ecology of Meso- and Bathypelagic Predatory Fishes in the Gulf of Mexico

The trophic ecology of eight circumglobal meso- and bathypelagic fishes ( Anoplogaster cornuta , Chauliodus sloani , Coccorella atlantica , Gigantura chuni , G. indica , Omosudis lowii , Photostomias guernei , and Stomias affinis ) with contrasting vertical migration habits (vertical migrators vs. non-migrators) were examined using stable isotope analysis (SIA). Mean δ ¹³ C values of these predators were similar among species, ranging from –18.17 to –18.99 ‰, suggesting that all species are supported by a similar carbon source. This finding was supported by mixing-model analysis; all of these deep-living predators received the majority (>73%) of their carbon from epipelagic food resources. Mean δ ¹⁵ N values of the predators ranged from 9.18 to 11.13 ‰, resulting in trophic position estimates between the third and fourth trophic level, although significant shifts in δ ¹⁵ N with increasing body size suggest that some of these species undergo ontogenetic shifts in trophic position. Bayesian standard ellipses, used to estimate isotopic niche areas, differed in size among species, with those occupying the highest relative trophic positions possessing the largest isotopic niches. These results, which provide the first trophic descriptions using dietary tracers for several of these species, offer insight into the trophic structure of deep-sea ecosystems and will help inform the construction of ecosystem-based models.