Larval fish assemblages and associations in the north-east Pacific Ocean along the Oregon coast, winter-spring 1972–1975

Abstract

Consistent patterns of larval fish distributions were found to occur along the Oregon coast between the Columbia River and Cape Blanco during winter-spring months for the years 1972–1975. Six data sets from March 1972, April 1972, March 1973, April 1973, March 1974 and March 1975 were analyzed using the pattern recognition techniques of numerical classification. Data included 306 bongo net samples containing 34 029 larval fish in 93 taxa. Coastal, transitional, and offshore assemblages (station groups) were present in each of the sampling periods. The region of transition from coastal to offshore assemblages roughly paralleled the shelf-slope break. Coastal and offshore species associations (species groups) were also always present. Species in the coastal and offshore groups never co-occurred. The consistency of these patterns is probably related to the spawning location of adults and to the predominate longshore coastal circulation patterns.

Differences in the extent of offshore distribution of the coastal assemblages among years reflected differences in local coastal wind patterns. Differences in the dominant taxa and their relative abundances within assemblages may reflect variation in timing of spawning and survival of larvae in the planktonic phase.

Despite the differences, the persistent occurrence of three major assemblages, coastal, transitional and offshore, and three major species groups from year to year supports the idea that these patterns of larval fish distributions are constant features over the continental shelf region off Oregon. The constancy of these patterns over four years suggests that transport may not be a major cause of larval fish mortality and recruitment failure in this region.