Larger Predatory Fishes of the Meso- and Bathypelagic Domains: Linking the Planktivores and Top Predators

Mesopelagic fish biomass has been estimated at 7–10 billion metric tons, an order of magnitude higher than previous estimates. This upscaling has resulted from the acoustical quantification of net avoidance, particularly avoidance of smaller, research-sized nets such as rectangular midwater trawls (RMTs) upon which previous estimates were based. Net avoidance by fishes is size-dependent, thus our greatest underestimation is likely that of the larger deep-pelagic fishes. Here, we present results from a research program in the Gulf of Mexico that used a large, dual-warp pelagic trawl in concert with an opening-closing RMT to sample from 0-1500 m depth. A total of 129 quantitative samples were obtained with the large trawl, representing over 337 million cubic meters of water filtered. Results showed a stark difference in both the size class and taxonomic composition of fishes collected with the two gears. Some of the larger, predatory deep-pelagic fishes collected were dragonfishes, anglerfishes, great swallowers, pelagic eels, and snake mackerels. Aspects of faunal composition, abundance, biomass, and size distributions will be presented. These larger deep-pelagic fishes are preyed upon by top predators such as sharks, billfishes, tunas, toothed whales, and deep-demersal fishes. Thus, data from this study will help improve our understanding of the links between zooplanktivorous micronekton and apex predators. The inclusion of large deep-pelagic fish biomass should dramatically improve ecosystem modeling efforts aimed at understanding carbon flow in the deep ocean interior. http://www.deependconsortium.org