Biological indicators of the timing and direction of warm-water advection during the 1997/1998 El Niño off the central Oregon coast, USA

Abstract

Unusual collections of several euphausiid, chaetognath, and copepod species help eluci- date the effects of the strong 1997/1998 El Nino off the central Oregon, USA, coast. Furcilia of Nycti- phanes simplex, a euphausiid typically found only as far north as central California, were collected in bi-weekly nearshore samples between December 1997 and November 1998. N. simplex was reported in summer 1998 as far north as the northern tip of Vancouver Island, British Columbia, Canada (51° N); our bi-weekly collections off Oregon allow us to use that species to help resolve the timing of arrival and disappearance of the biological signal of the El Nino, which was delayed by several months beyond the physical signal. Additionally, 2 species of euphausiid (Euphausia recurva and E. mutica), 2 species of chaetognath (Sagitta pseudoserratodentata and S. hexaptera), and 1 copepod (Centropages bradyi) that have never before been reported in coastal Oregon waters were collected in samples taken between 28 and 103 km off Oregon during the 1997/1998 El Nino. The 1997/1998 El Nino was one of the strongest on record and the occurrence of the unusual species may indicate the extent of the northward and onshore advection of warm water into the study area.