Patterns in micronekton diversity across the North Pacific Subtropical Gyre observed from the diet of longnose lancetfish (Alepisaurus ferox). (July 2017)

• Record Type: Journal Article
• Authors: Portner, Elan J.; Polovina, Jeffrey J.; Choy, C. Anela
• Is Part Of: Deep sea research. Volume 125(2017)
• Page Start: 40
• Page End: 51
• Publication Date: 2017-07
• Subjects: Pelagic ecology -- Trophic dynamics -- Mesopelagic predator -- Diet analysis -- Biological sampler -- Lancetfish -- Micronekton -- North Pacific Subtropical Gyre -- Midwater communities -- Classification and Regression Trees; Oceanography -- Periodicals; Océanographie -- Périodiques; 551.4605
• DOI: 10.1016/j.dsr.2017.04.013
• Languages: English
• ISSNs: 0967-0637

Abstract

Abstract: We examined the diet of a common midwater predator, the longnose lancetfish ( Alepisaurus ferox, n=1371), with respect to fork length, season, and capture location within the North Pacific Subtropical Gyre (NPSG). While A. ferox fed diversely across 97 prey families, approximately 70% of its diet by wet weight consisted of seven prey families (fishes: Sternoptychidae, Anoplogastridae, Omosudidae, Alepisauridae; hyperiid amphipods: Phrosinidae; octopods: Amphitretidae; polychaetes: Alciopidae). Altogether, these micronekton prey families constitute a poorly known forage community distinct from those exploited by other pelagic predators and poorly sampled by conventional methods. We demonstrate ontogenetic variation in diet between two size classes of A. ferox (<97 cm fork length="small", ≥97 cm fork length="large"). Large A. ferox consumed more fish and octopods, fewer crustaceans, and were more cannibalistic than small A. ferox . Ontogenetic shifts in vertical foraging habitat were observed as the consumption of larger and more mesopelagic prey with increasing fork length. Spatial and seasonal variation in the diet of A. ferox is consistent with expected patterns of variation in prey distribution with respect to oceanographic features of the NPSG. Within both size classes, the diets of specimens collected from the oligotrophic core of the NPSG were more diverse than those collected near the boundaries of the gyre and appeared to track seasonal variation in the position of the northern boundary of the gyre. Our data suggest seasonal and spatial variability in the composition of midwater forage communities exploited by A. ferox across the NPSG, and demonstrate that sustained monitoring of diet could provide valuable insights into long-term changes in these understudied communities. Highlights: Lancetfish consume a high diversity of poorly known micronekton prey. Diet varies in a predictable way across the North Pacific Subtropical Gyre. Unique prey and cannibalism may help explain prevalence of lancetfish in North Pacific. Lancetfish are useful biological samplers of midwater prey communities.