A COMPARISON OF LARVAL FISH ASSEMBLAGES IN THE TEMPERATE ZONE OF THE NORTHEAST PACIFIC AND NORTHWEST ATLANTIC OCEANS

Numerical classification is used to examine broad scale spatial patter ns in the larval component of the ichthyoplankton off the west and eas t coasts of the United States, based on data collected during extensiv e surveys over several years. The multispecies spatial patterns that e merged imply the existence of persistent and geographically distinct l arval fish assemblages off both coasts. Four assemblages were identifi ed off the west coast. They include a coastal assemblage that was rest ricted to coastal and continental shelf waters mainly off Washington a nd Oregon; a slope/transitional assemblage that occurred largely along the shelf edge and slope; a Columbia River plume assemblage that was associated with the Columbia River plume during summer; and an oceanic assemblage that prevailed in deep water beyond the shelf edge and for which northern and southern components were apparent during winter an d spring. The east coast assemblages include a Gulf of Maine and Georg es Bank assemblage; an oceanic assemblage that was associated with the continental shelf edge and slope; and a Middle Atlantic Bight assembl age that occurred along the shelf from Cape Cod, Massachusetts, to Cap e Hatteras, North Carolina, Northern, southern, inshore, and offshore components of the Middle Atlantic Bight assemblage were apparent at ce rtain times of the year. In general, the boundaries to the assemblages are fluid, and seasonal variation in occurrence and abundance of spec ies within assemblages is strong. The distribution of the larval fish assemblages reflects spatial structure in the oceanographic environmen t and, in some instances, can be related to specific hydrographic feat ures. Among the fish taxa in both regions, adaptation of the spawning patterns to the prevailing oceanographic conditions is apparent. Co-ev olution among the fishes' spawning strategies within the complex and v ariable marine ecosystems may have given rise to the high degree of st ructure observed in the ichthyoplankton spatial patterns and to the la rval fish assemblages themselves. It is not possible to conclude from this limited study that the multispecies larval fish assemblages are i ndependent ecological entities that enhance survival of the constituen t species. Further investigations of finer scale spatial patterns with in the larval fish assemblages and among different ontogenetic categor ies, as well as consideration of the zooplankton, of which fish larvae form only a small part, are necessary to understand fully the multisp ecies spatial patterns that prevail.