US GLOBEC Newsletter 14: Marine Nekton

| Effects of the 1997-98 El Niño on Marine Nekton Off Oregon by William G. Pearcy
Also in This Issue .... LTOP in the NEP Zooplankton in OR Coastal Zone El Niño Affects Marine Nekton GLOBEC Studies in the CGOA GoMex Workshop - Summary Cod & Climate Change Program Notes From the Field .... Sea Scallop Fishery Closures
The 1997-98 El Niño, like the 1982-83 event, was very strong. Both of these El Niños had dramatic effects on the physical oceanography and biology along the Oregon coast, but the biological response to the 1997-98 event was very different from the earlier El Niño. During the late summer and fall of 1997, warm-water, oceanic fishes were commonly caught or sighted off the Oregon coast. The first record was of a dorado, Coryphaena hippurus, in late July, followed by yellowtail, Seriola lalandi, yellowfin tuna, Thunnus albacares, and striped marlin, Tetrapturus audux, in September. In addition, albacore (tuna), Thunnus alalunga, were caught in commercial quantities in the warm water very close to shore, and some individuals were exceptionally large, over 50 pounds. Pacific markerel (Scomber japonicus) and jack mackerel (Trachurus symmetricus) were other warm water species found close to shore and even in estuaries along the coast. All of these fishes are strong migrators that are usually associated with warm surface waters. The influx of uncommon epipelagic animals during the 1997-98 El Niño .... was quite different from the preponderance of unusual epibenthic animals during the 1982-83 event .... The most unusual nektonic animal that invaded Oregon waters was the jumbo squid, Dosidicus gigas. This large, voracious squid has been reported off California during previous large El Niños, but this is the first record as far north as Oregon. It was so common off Oregon during September through December of 1997, that commercial trawlers were targeting it for a lucrative squid market in southern California. Except for a striped marlin, epipelagic nekton were not reported during 1998. Instead, several species of coastal and demersal fishes were caught from April through June. These species included the lumptail searobin, Prionotus stephanophyrs, the popeye catalufa, Pseudopriacanthus serrula, and the California barracuda, Sphyraena argentea. Based on these observations of nektonic animals, the influx of large oceanic fishes and squid from July through September 1997 was related to the advection of warm oceanic waters from offshore due to atmospheric forcing rather than coastally-trapped Kelvin waves along the coast, which did not arrive until later in the year, as indicated by the deep pool of warm water and northward advection (see GLOBEC's LTOP in the NEP). The coastal and benthic fishes found in 1998, as well as the occurrence of the euphausiid, Nyctiphanes simplex (see Zooplankton in the OR Coastal Zone), however, could be the result of coastal transport from California waters. These observations for the 1997-98 El Niño are quite different than those for the 1982-83 event. During 1982-83 most of the unusual animals, including eight of nine range extensions, were for coastal, epibenthic animals presumably transported by coastal currents from the south (Pearcy & Schoener, 1987). In contrast, in 1997-98 most of the unusual sightings were of large migratory, offshore, epipelagic animals that moved into coastal waters that were exceptionally warm because of onshore transport and lack of effective coastal upwelling. During the 1983 El Niño, unprecedented mortality of coho salmon occurred off Oregon and California, and the mean size of adult salmon was markedly reduced. Such dramatic changes were not obvious during 1998. Ocean survival of hatchery coho salmon from Oregon has been very low (< 1%) since 1993, which is even lower than the rate of ocean survival for 1983. The mean length of Oregon coho salmon was low in 1983 and 1992, and has increased in recent years, suggesting density-dependent growth. Literature Cited: Pearcy, W.G. and A. Schoener. 1987. Changes in the marine biota coincident with the 1982-1983 El Niño in the northeastern subarctic Pacific Ocean. J. Geophys. Res. 92, No. C13: 14417-14428. Last updated: 14 October, 1999 Please address any comments, suggestions or questions to: GLOBEC Webmaster