A Diet Analysis of Wahoo (Acanthocybium solandri) From Pelagic and Hawaiian Nearshore Ecosystems Using Visual and DNA Metabarcoding Techniques

Abstract

Diet studies are an informative way to gather information on the ecology of a given organism, as well as the environment that organism inhabits. Wahoo (Acanthocybium solandri) is a globally popular commercial, sport, and recreational fish species but currently, detailed information is lacking on their diet composition. In the Central North Pacific we collected 233 stomachs from the offshore Hawaiian longline fishery, as well as 211 stomachs from the Hawaiian nearshore troll fishery from June to December 2014. Stomach contents can be difficult to identify when nearly digested, limiting the ability to identify prey items visually. To increase the taxonomic resolution of prey identifications, the CO1 region of the mtDNA genome was sequenced for individual prey items that could not be identified to species level visually. Clear spatial and temporal shifts in prey composition were observed in both fisheries. For nearshore-caught wahoo, juvenile pre-settlement reef species from various families (primarily Heteropriacanthus cruentatus (Priacanthidae) dominated the prey composition during the summer months, followed primarily by Decapterus macarellus (Carangidae), in the fall months. Gempylus serpens (Gempylidae), Remora brachyptera (Echeneidae), and Katsuwonus pelamis (Scombridae) were common prey taxa for wahoo collected from the offshore fishery. Clear spatial patterns were seen for two prey families. Ranzania laevis (Molidae) was a common prey item and was usually found in stomachs collected northeast of the Hawaiian Archipelago. Tetraodontiform reef fishes present in stomachs from the offshore fishery were Melichthys niger (Balistidae) and diodontids all known to have extended pelagic stages prior to reef settlement and were present in stomachs collected southwest of the Hawaiian Archipelago. The endoparasitic digenetic trematode Hirudinella ventricosa was observed in 98% of wahoo stomachs. The diet composition of wahoo was indicative of an opportunistic feeder and thus revealed dominant geographic and seasonal abundances of certain taxa from various ecosystems in the marine environment. Further, the addition of molecular barcoding to the traditional visual method of prey identifications allows for a more comprehensive range of the prey field of the predator to be elucidated.