EXPLORATIONS OF EL NINO EVENTS AND ASSOCIATED BIOLOGICAL POPULATION DYNAMICS OFF CENTRAL CALIFORNIA

Abstract

During El Niiio events off central California, tem- peratures were elevated, salinities were depressed, and there was evidence of poleward and onshore advection. El Niiio conditions seemed to delay the annual phyto- plankton bloom, affect the distribution and abundance of invertebrates, improve recruitment of southern fish species, cause recruitment failures of rockfish (Sebustes spp.), and cause poor growth and condition of adult rock- fish. The 1992-93 El Niiio off central California was less extreme than the 1982-83 event, but much stronger than the 1986-87 event. Water temperatures in 1992-93 were similar to the 1982-83 event, but poleward advec- tion appeared to be weaker. Recruitment of southern species was higher in 1983 than in 1992; the condition of rockfish was better in the more recent event. Computer simulation indicated that fishery management practices can influence the intensity of El Niiio effects on a fish- ery for rockfish. Possible causes of rockfish recruitment failures during El Niiio events are discussed. INTRODUCTION Scientists familiar with waters off central California (figure 1) are aware that significant physical and biolog- ical changes are associated with El Niiio events. However, little of the extensive scientific literature on El Niiio events emphasizes central California. In this paper, we review some of the important papers dealing with El Niiio characteristics in the northeastern Pacific Ocean, and then explore El Niiio-related phenomena off cen- tral California, emphasizing the 1992-93 event, but also including the 1957-59, 1982-83, and 1986-87 events. We first examine physical oceanographic data, &om shore stations and from oceanic surveys. We next present bi- ological information for trophic levels ranging from pri- mary production to planktivores. Finally, we show results of a computer simulation of El Niiio effects on an ex- ploited population of rockfish. Most of the biological data come from research by the authors or close associates and have not been previ- ously published in the peer-reviewed literature. Because of the review nature of this paper and the wide scope of