NEUSTONIC ICHTHYOPLANKTON IN THE WESTERN GULF OF ALASKA DURING SPRING

Species diversity and abundance of fish eggs in shelf waters of the we stern Gulf of Alaska were similar in both surface neuston net tows and subsurface bongo net tows, but a unique group of fish larvae appear t o be associated with the neuston in this region. The dominance of larv ae of an osmerid, several hexagrammids, cottids, bathymasterids, Anopl opoma fimbria, Cryptacanthodes aleutensis, and Ammodytes hexapterus in this group resembles the neustonic assemblage of fish larvae found in the California Current region along the U.S. west coast and most of t hese taxa are considered obligate members of the neuston. Several taxa , however, appear to be abundant in the neuston only at night suggesti ng a facultative association with the neuston through a diel pattern o f vertical migration. The facultative association of certain species o f larvae with the neuston varies with larval size. The distribution pa tterns observed for most taxa of fish larvae in the neuston during thi s study suggest that during spring, spawning and emergence of larvae i nto the plankton and subsequently into the neuston take place mainly a round Kodiak Island (except along the seaward side) and along the Alas ka Peninsula to the southwest. Analysis of multispecies spatial patter ns using recurrent group analysis and numerical classification did not reveal the existence of more than one neustonic assemblage of fish la rvae in the study area. Apart from perhaps Pleurogrammus monopterygius larvae, which are known to occur throughout the Gulf of Alaska, and t o a lesser extent A, fimbria and Hemilepidotus hemilepidotus, members of this neustonic assemblage of larvae are not commonly found in the o ceanic zone. The ecological significance of a neustonic existence for larvae of fish that are primarily demersal spawners in the Gulf of Ala ska is considered to be trophic in nature. Neustonic fish larvae seem to be able to exploit to their advantage the unique feeding conditions which exist at the sea surface.