DISTRIBUTION, SIZE, AND ABUNDANCE OF MICROCOPEPODS 



IN THE CALIFORNIA CURRENT SYSTEM AND THEIR POSSIBLE 



INFLUENCE ON SURVIVAL OF MARINE TELEOST LARVAE 1 



David K. Arthur 2 



ABSTRACT 



The California Current system can be divided into onshore and offshore faunal zones by a copepod 

 indicator species, Mecynocera clausii. Near the outer edge of the onshore zone copepod nauplii densities 

 were higher than usual. There were about 3 times as many microcopepodids and 12 times as many 

 nauplii on the average throughout the onshore as in the offshore zone. Feeding habits of larvae of 

 sardines, anchovies, and jack mackerel may be adapted to the usual naupliar and copepodid concen- 

 trations of the zone in which they were spawned. The usual concentration of 56- /um and wider nauplii 

 in the onshore zone was about 3/liter with 17/liter the highest observed which indicates that for 

 nauplii of all sizes there were usually about 36/liter and with the highest density of 195/liter. These 

 concentrations are lower than has usually been reported to be required for rearing larval fish in 

 laboratories. Numbers of nauplii decreased exponentially with increasing size but a naupliar biomass 

 maximum was found to occur at about the 70 /xm width. Nauplii of this size are ingested at first 

 feeding by Pacific sardine, northern anchovy, and jack mackerel larvae. It is suggested that larval 

 feeding habits of these fish have evolved to utilize this important food resource at their first feeding. 



Copepods form the bulk of most zooplankton hauls 

 from the sea and are important because they are 

 the main convertors of phytoplankton into food 

 suitable for higher organisms (Marshall 1973). 

 Copepods are especially important as food for 

 planktonic larvae of pelagic marine teleosts. Food 

 of the larvae of commercially important marine 

 fishes has been widely reported as being primarily 

 eggs, nauplii, and copepodid stages of small cope- 

 pods. Yokota et al. (1961) found that food occur- 

 ring in the feeding larvae of all the 57 species 

 taken in their primarily coastal samples was 

 almost entirely small copepods, especially nauplii. 

 Duka and Gordina (1973) investigated the food of 

 larvae of 26 species of teleosts from the Medi- 

 terranean and adjacent areas of the Atlantic and 

 reported that copepod nauplii composed 90% of 

 all items eaten by small larvae (2.3 to 5.0 mm). 

 Stomach content analyses of fish larvae are also 

 corroborated by population dynamic studies of 

 plankton organisms. Fish ( 1936) noted that in the 

 Gulf of Maine a small copepod, genus Pseudo- 

 calanus, suffers a much higher predation rate 



■Based on a portion of a dissertation submitted in partial 

 satisfaction of the requirements for the Ph.D. degree at the 

 University of California, Scripps Institution of Oceanography. 



2 Senior Research Associate, National Academy of Science, 

 Southwest Fisheries Center, National Marine Fisheries Service, 

 NOAA, P.O. Box 271, La Jolla, CA 92038. 



Manuscript accepted January 1977. 

 FISHERY BULLETIN: VOL. 75, NO. 3, 1977. 



during the naupliar stages than does Calanus 

 finmarchicus whose eggs (140 /xm wide) and nau- 

 plii are too large to be. ingested by many fish 

 larvae. 



When it became apparent that the population 

 of Pacific sardine, Sardinops sagax, was in 

 serious decline, a research program [later to 

 become known as CalCOFI (California Coopera- 

 tive Oceanic Fisheries Investigations)] was initi- 

 ated in 1949 to investigate the ecology of this 

 important fish. One part of this investigation was 

 a study of the food and food resources of sardine 

 larvae and consisted of two main objectives: 

 1) determine what the larvae eat, and 2) to study 

 the abundance and distribution of these food 

 items. The ultimate purpose was to determine if 

 feeding conditions, especially for the first feeding 

 larvae, could be a contributing factor to the sar- 

 dine's decline, as was proposed by Hjort (1914) 

 to explain poor year class survival of fishes in 

 general. 



The identifiable food of first feeding sardine 

 larvae was primarily copepod nauplii ranging 

 from 25 to 80 fxm but mostly about 70 /xm wide 

 (Arthur 1976). Nauplii of this size are produced 

 only by small species of copepods, roughly less 

 than 1.5 mm long. The assemblage of these small 

 copepods is composed of many species. Several 

 genera have often been recorded as being abun- 



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