Abundance and distribution of ichthyoplankton in the upwelling zone off Oregon during anomalous El Niño conditions

The abundance and distribution patterns of nearshore ichthyoplankton were investigated during a year of anomalously high sea temperatures off Oregon. Samples collected from 2 to 18 km offshore from April through September of 1983 showed increased occurrences and higher abundances of taxa usually found at distances offshore of 37 km in other years. The dominant species collected, comprising more than half of the total larval fish abundance, was the northern anchovy (Engraulis mordax). Larval anchovy have rarely been collected inshore in previous studies. Many of the dominant taxa normally found inshore, especially osmerids, were present in reduced numbers in 1983. Changes in the hydrographic conditions associated with onshore surface drift and reduced summer upwelling during the 1983 El Niño could explain the distributional patterns observed. The warm inshore waters apparently provided a substantial spatial and temporal expansion of the spawning habitat for E. mordax.