FIELD CRITERIA FOR SURVIVAL OF ANCHOVY LARVAE: 



THE RELATION BETWEEN INSHORE CHLOROPHYLL MAXIMUM 



LAYERS AND SUCCESSFUL FIRST FEEDING' 



Reuben Lasker^ 



ABSTRACT 



Northern anchovy larvae, Engraulis mordax, produced by laboratory-spawned fish, have been used to 

 detect concentrations of larval fish food in situ along the California coast. First-feeding larval 

 anchovies, whose development was controlled by temperature manipulation aboard ship, were placed in 

 samples of Los Angeles Bight water taken from the surface and from chlorophyll maximum layers. 

 Feeding by larvae in water from the surface was minimal in all experiments but extensive feeding 

 occurred in water from the chlorophyll maximum layers when these contained phytoplankters having 

 minimum diameters of approximately 40 ju,m and which occurred in densities of 20 to 40 particles/ml. 

 In March and April 1974, the chlorophyll maximum layer along the California coast from Malibu to San 

 Onofre (a distance of about 100 km) consisted chiefly of a bloom of the naked dinoflagellate Gym- 

 nodinium splendens, a food organism known to support growth in anchovy larvae. Copepod nauplii and 

 nonliving particles were never in high enough concentration or of the proper size to be eaten by the 

 larvae. A storm which caused extensive mixing of the top 20 m of water obliterated the chlorophyll 

 maximum layer and effectively destroyed this feeding ground of the larval anchovy. 



Probably the major problem confounding fishery 

 scientists interested in rational management of 

 fisheries is an inability to predict recruitment 

 failure (Gulland 1973) despite the vast amount of 

 laboratory and field work on food chain analysis 

 leading to fish production which has occupied 

 many workers in marine studies for the past two 

 decades (Steele 1970). Gulland (1973) asks the most 

 pressing question, "Can a study of stock and 

 recruitment aid management decisions?" and in 

 the same article answers "No." This pessimistic 

 reply is given because, as he says, "there is no 

 method which is likely to be generally successful, 

 [because] the most promising depends on lengthy 

 and costly collection of data, probably extending 

 over a long period." The work reported in this 

 paper suggests an approach which has not been 

 previously used in fishery research as far as I am 

 aware, and which, I believe, makes the answer 

 Gulland has given somewhat less pessimistic than 

 when he made it. 



However, it is generally agreed among fishery 

 biologists that large spawning populations of fish 



'MARMAP (Marine Resources Monitoring, Assessment, and 

 Prediction) Contribution No. 17. 



Southwest Fisheries Center La Jolla Laboratory, National 

 Marine Fisheries Service, NOAA, La Jolla, CA 92037. 



Manuscript accepted November 1974. 

 FISHERY BULLETIN: VOL. 73, NO. 3, 1975. 



do not ensure subsequent large year classes, and 

 conversely, small spawning populations oc- 

 casionally give rise to exceptionally large classes 

 (Hjort 1926). Hjort (1914) postulated that these 

 variations in year class strength are probably due 

 to differential mortality of the larvae. He 

 believed, for example, that the larvae of the Nor- 

 wegian herring, Clupea harengus, suffered huge 

 mortalities resulting in small year classes when 

 there was a lack of food for the first-feeding lar- 

 vae. The attractiveness of this hypothesis has 

 generated a number of laboratory studies (see, for 

 example, Lasker et al. 1970) which have shown that 

 the density of larval food must be higher than that 

 usually found at sea in order to obtain even 

 moderate larval growth and survival. For an in- 

 depth discussion of the larval "critical period" as 

 affected by food see May (1974), and for a review 

 of laboratory attempts to rear fish larvae, refer to 

 May (1971). The conclusion that the mean density 

 of larval food organisms in the ocean is generally 

 too low to support reasonable survival of fish lar- 

 vae through metamorphosis, is also substantiated 

 by data from field surveys (Beers and Stewart 

 1967, 1969). Thus, despite extensive efforts in 

 quantitative marine food chain analysis, it is yet 

 to be demonstrated whether, where, and to what 

 extent there are rich feeding areas in the sea for 

 larval fishes. 



453 



