Epipelagic nekton of the North Pacific Subarctic and Transition Zones

During the 1980s and 1990s, scientific research cruises and commercial gill net operations with scientific observers aboard were conducted throughout m uch of the Subarctic and Transition Zones of the North Pacific Ocean, These studies produced one of the most extensive databases ever collected on the relative species composition and trophic structure of epipelagic nekton of the Subarctic and Transition Zones in the North Pacific Ocean. Data from J apanese high-seas gillnet research surveys (1981-1991) were examined using multivariate analytical techniques to analyse community structure of nekton ic cephalopods, elasmobranchs, and teleosts in the North Pacific Subarctic and Transition Zones during the summer months, emphasizing differences betw een the eastern and western Subarctic Gyres, Species diversity generally in creased going from west to east, which was apparently associated with the g reater range of temperatures in the east. Discriminant analysis was able to correctly classify about half the catch locations into their respective re gions. Catches from multinational drift gillnet commercial fisheries operat ions in 1990-1991 mainly in the Transition Zone were also examined, Classif ication techniques were employed to determine species associations and mult ivariate analyses were used to examine relationships of these assemblages t o environmental data. We found that some species are often captured in the same gillnet sets and form species associations that are distinct in ordina tion space, but these associations are loose and map vary appreciably from year to year, We review recent studies on the feeding habits and daily rati on of the dominant species and construct food webs for the eastern and west ern Subarctic and Transition Zone systems emphasizing the role that nekton play in these pelagic ecosystems. (C) 1999 Elsevier Science Ltd. All rights reserved.