EFFECTS OF AN EL NINO EVENT ON THE FOOD HABITS OF 



LARVAL SABLEFISH, ANOPLOPOMA FIMBRIA, 



OFF OREGON AND WASHINGTON 



Jill J. Grover^ and Bori L. Olla^ 



ABSTRACT 



The effect of El Nino conditions on the food habits of larval sablefish, Anoplapoma fimbria, was examined 

 by comparing the diet of larvae collected off Oregon and Washington during the 1983 El Nino event 

 and during 1980, a year in which conditions were not anomalous. While differential utilization of appen- 

 dicularians, pteropods, and amphipods was seen in the 2 years, the most notable difference was that 

 small copepods contributed significantly more to the diet in 1983 than in 1980. Dietary data for 1983 

 were generally supported by independent plankton observations, especially with respect to the pre- 

 dominance of Paracalanus parvus, a small calanoid copepod. Because adult sablefish live and spawn 

 in deep water, changes in the food habits of neustonic larvae may represent one of the principal effects 

 of the El Niilo conditions on this species. 



Larvae represent a precarious stage in the life 

 history of marine fishes as they are highly vulner- 

 able to fluctuations in oceanographic conditions and 

 food resources. Their survival is dependent on suc- 

 cessful feeding, avoidance of predation, and favor- 

 able transport (Sinclair et al. 1985). The relative 

 importance of these factors is difficult to assess since 

 each varies with species, developmental stage 

 (Hewitt et al. 1985), and environmental conditions. 

 Additionally, these sources of mortality are inter- 

 active insofar as the transport of larvae into areas 

 with suboptimal feeding conditions may result in 

 starvation, and starving larvae are at greatest risk 

 for predation. Because survival past the larval and 

 early juvenile stages clearly depends on successful 

 feeding, understanding the success of larval popula- 

 tions requires a thorough knowledge of feeding 

 ecology. As a result, in recent years a number of 

 studies have provided detailed descriptions of the 

 food habits of marine fish larvae (e.g., Laroche 1982; 

 Cohen and Lough 1983; Govoni et al. 1983; Gadom- 

 ski and Boehlert 1984; Brewer and Kleppel 1986), 

 and a few studies have documented the occurrence 

 of starvation under natural conditions (O'Connell 

 1980; Hewitt et al. 1985; Grover and 011a 1986; 

 Theilacker 1986). The present study examined the 

 food habits of larval sablefish, Anoplopoma fimbria, 



collected during 2 years of differing oceanographic 

 conditions. 



As oceanographic conditions are manifested 

 through changes in zooplankton assemblages, 

 between-year comparisons of the diet of larval fishes 

 can reflect differences in oceanic conditions. Such 

 comparisons are of particular interest when they in- 

 clude periods characterized by highly anomalous 

 conditions. One such oceanographic anomaly, an El 

 Nino event, occurred in the eastern Pacific Ocean 

 off North America from the fall of 1982 through late 

 summer 1983. 



The magnitude of El Nino-induced anomalies in 

 physical conditions appears to be greatest in surface 

 waters, with anomalous conditions having the great- 

 est effect on those life stages of fishes that occupy 

 the upper water column. Adult sablefish inhabit deep 

 slope waters and spawn at depths in excess of 300 

 m (Mason et al. 1983), and therefore may be rela- 

 tively insulated from El Nino conditions (Bailey and 

 Incze 1985). Their eggs may also be insulated, as 

 they hatch in water deeper than 400 m (Mason et 

 al. 1983). However, larvae ascend to surface waters 

 where they reside through early juvenile stages 

 (Shenker and 011a 1986; J. M. Shenker^). During this 

 neustonic phase they are most vulnerable to anom- 

 alous oceanographic conditions. While El Nifio con- 



'College of Oceanography, Oregon State University, Hatfield 

 Marine Science Center, Newport, OR 97365. 



^Cooperative Institute for Marine Resources Studies, Northwest 

 and Alaska Fisheries Center, National Marine Fisheries Service, 

 NOAA, Hatfield Marine Science Center, Newport, OR 97365. 



^Shenker, J. M. Oceanographic associations of neustonic lar- 

 val and juvenile fishes and Dungeness crab megalopae off Oregon. 

 Manuscr. in prep. University of California, Bodega Marine 

 Laboratory, Bodega Bay, CA 94923. 



Manuscript accepted August 1986. 



FISHERY BULLETIN: VOL. 85, NO. 1, 1987. 



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