DISTRIBUTION OF ICHTHYOPLANKTON OFF SAN ONOFRE, 

 CALIFORNIA, AND METHODS FOR SAMPLING VERY SHALLOW 



COASTAL WATERS 



Arthur M. Barnett, 1 Andrew E. Jahn, 2 Peter D. Sertic, 1 

 and William Watson 1 



ABSTRACT 



Spatial abundance patterns of inshore marine fish larvae, together with day-night and ontogenetic changes in 

 these patterns, were investigated at a single site off the southern California coast using neustonic, midwater, 

 and epibenthic samplers. Fifteen of the nineteen most abundant taxa showed statistically significant abun- 

 dance patterns: Five taxa were principally in the inshore (<2 km from shore) epibenthos, one in the inshore 

 neuston, two in the neuston and midwater less than about 5 km from shore, three to midwater 2-5 km from 

 shore, and four in midwater offshore of about 3.5 km. Abundance patterns for the three most common taxa, 

 Engraulis mordax, Genyonemus lineatus, and Seriphus politus, shifted toward shore and toward the bottom 

 with increasing larval size. Comparison of E. mordax egg and larval abundances indicated a large excess of 

 larvae over eggs nearshore. Only two taxa showed statistically significant day-night pattern changes; both 

 were lower in the water column during the day. 



The existence of inshore abundance maxima implies significant survival value in occupying the nearshore 

 zone. The shallow waters of the southern California coast may represent a nursery area comparable in impor- 

 tance to the estuarine nurseries of the Atlantic coast of North America. 



Through the pioneering California Cooperative 

 Oceanic Fish Investigation (CalCOFI) work of the 

 late E. H. Ahlstrom and co-workers (Ahlstrom 1959, 

 1965), ichthyoplankton of the Southern California 

 Bight are generally well known. However, the 

 CalCOFI effort was concentrated on species found 

 principally offshore of the 100 m isobath, and the lar- 

 vae of most inshore fishes are rare or missing in the 

 published CalCOFI data. Recent studies of 

 ichthyoplankton in the Southern California Bight 

 inshore of the 100 m isobath (Brewer et al. 1981; 

 Gruber et al. 1982; Brewer and Smith 1982) have 

 indicated that many of these larvae are found in the 

 relatively shallow waters. 



In this paper we present methods for sampling 

 quantitatively the entire water column in shallow 

 waters (6-75 m) and describe the spatial abundance 

 patterns of the most commonly occurring larval 

 fishes. Of particular interest was the distribution of 

 larvae in the onshore-offshore vertical plane. 

 Ontogenetic pattern changes were investigated for 

 three abundant species: Engraulis mordax, Geny- 

 onemus lineatus, and Seriphus politus. 



'Marine Ecological Consultants of Southern California, 531 

 Encinitas Boulevard, Suite 110, Encinitas, CA 92024. 



2 Marine Ecological Consultants of Southern California, 531 

 Encinitas Boulevard, Suite 110, Encinitas, Calif.; present address: 

 Los Angeles County Museum of Natural Histoiy, 900 Exposition 

 Boulevard, Los Angeles, CA 90007. 



The study was done off San Onofre, Calif., (Fig. 1) 

 from September 1977 to September 1979. Unit 1 of 

 the San Onofre Nuclear Generating Station, a 500- 

 megawatt plant located 1.5 km northwest of the 

 sampling area, was operating continuously through- 

 out the course of the study. However, this plant has 

 been shown to have only very localized effects which 

 have not interfered measurably with the results 

 reported herein (Marine Review Committee 1979 3 ; 

 Bartlet et al. 198 1 4 ). This study was completed prior 

 to the beginning of operation of Units 2 and 3 of the 

 San Onofre Nuclear Generating Station. 



Our sampling methodology resulted from a pre- 

 liminary study in which we found that a combination 

 of sampling gear was necessary to estimate nearshore 

 larval abundance. The chief purpose of this paper is 

 to present these sampling methods. Results are 

 shown which verify the effectiveness of these 

 methods and further suggest some peculiarities of 

 the nearshore habitat. 



'Marine Review Committee. 1979. Interim report of the Marine 

 Review Committee to the California Coastal Commission. Part 1: 

 General summary of findings, predictions, and recommendations 

 concerning the cooling system of the San Onofre Nuclear Generating 

 Station. In Marine Review Committee Document 79-02, p. 1- 

 20. Marine Review Committee of the California Coastal Commis- 

 sion, 631 Howard Street, San Francisco, CA 94105. 



4 Barnett,A.M.,P.D. Sertic, and S.D. Watts. 1981. Final report: 

 Ichthyoplankton preoperational monitoring program. Marine 

 Ecological Consultants of Southern California, 531 Encinitas 

 Boulevard, Encinitas, CA 92024, 8 p. 



Manuscript accepted June 1983. 



FISHERY BULLETIN: VOL. 82, NO. 1. 1984. 



97 



