Seasonal and spatial patterns of ichthyoplankton abundance in Elkhorn Slough, California

Abstract

Seasonal and spatial patterns in abundance of fish eggs and larvae are described from 323 samples collected from September 1974–September 1976 in Elkhorn Slough, a shallow, tidal embayment in Monterey Bay, California. These included 3645 larvae of 29 taxa that were numerically co-dominated by gobiid and clupeoid larvae. Ninety-four percent of the total catch comprised seven species, and included, in rank order abundance, Gillichthys mirabilis, Engraulis mordax, Clevelandia ios, Hypomesus pretiosus -osmerid, Leptocottus armatus, Genyonemus lineatus , and Clupea pallasii . Eggs of E. mordax, Citharichthys spp., and G. lineatus accounted for 73% of the catch. Two seasonal groups of larvae were evident. E. mordax and the gobiids ( G. mirabilis and C. ios ) formed a summer-fall group. While more speciose, a winter and early-spring group comprised of larval L. armatus, H. pretiosus -osmerid, Atherinidae and Ammodytes hexapterus was not as abundant as the summer–fall assemblage. Egg densities were overwhelmingly high in summer, due almost entirely to E. mordax . Similarity in species composition was greatest between collections from the most inland stations; larval assemblages from near-ocean stations were least similar to the inland slough assemblages. These distributions are attributed to reproductive specializations (egg type and spawning origin of adults) and hydrographic conditions.