glass side and a capacity of about 1 ,500 liters were de- 

 signed. These tanks were painted matte green inside to 

 reduce liglit retlection in the corners. The aquaria are 

 filled with sea water from the main laboratory supply, 

 and a slow upwelling of water is induced in each by a 

 fine airstream. Only distilled water to replace evapora- 

 tion is added. 



Sardine and anchovy larvae prefer high levels of 

 illumination during the first week of feeding, and they 

 aggregate in areas of highest light intensity until they are 

 about 15 mm. long, when they move gradually deeper in 

 the aquarium. Four lOO-watt (or 24,000 lumen) mer- 

 cury vapor lamps produce sufficient light with low heat. 

 Continuous illumination is used to allow the larvae to 

 feed uninterruptedly. 



A bloom of Chhrella-Wke species of algae is per- 

 mitted to develop in the aquarium several days before 

 eggs are stocked. The primary purpose is to provide food 

 for the large numbers of copepod nauplii and copepodites 

 added later, when the fish are ready to feed. 



Sardine and anchovy eggs, together with those of 

 other species, are collected at sea off La Jolla by towing 

 a 1-m. plankton net close to the surface. Up to 20,000 

 eggs are put in each aquarium, and very higli percentages 

 of them hatch successfully. 



When the larvae are ready to feed, collections of 

 food organisms are made each day with a fine-meshed 

 tow net in Mission Bay, San Diego. Collections are re- 

 turned to the laboratory in buckets, larger organisms are 

 removed by straining the catch through a 260 micron 

 plankton mesh, and the contents of each bucket poured 

 into larger tanks where the copepods may be concen- 

 trated with a point source of light and collected with a 

 siphon. 



Wlien food organisms are relatively scarce, larvae 

 cannot be cultured with a reasonable chance of success 

 in large volumes of water, because few larvae survive in 

 low concentrations of food. A method of confining 

 larvae in relatively small volumes of water was developed 

 to permit larvae to be cultured successfully during these 

 periods. The method consisted of rearing larvae in very 

 thin (0.0025 mm.) polythene bags during the early criti- 

 cal days of active feeding. The bags are filled with green 

 water and are suspended in the large aquaria by an air- 

 infiated plastic ring. The bags are fully expanded by fill- 

 ing with water slightly above the water level in the 

 aquarium. An airstream in the aquarium circulates water 

 around the bag, and the thin plastic wall acts as a semi- 

 permeable membrane, permitting gaseous exchange. The 

 thin plastic wall of the bag apparently possesses sufficient 

 elasticity to prevent larvae from injuring themselves when 

 they swim into it. After larvae have grown to a length of 

 about 8 mm. and are able to swim well, the bag is slit 

 open and the fish are released in the larger area of the 

 aquarium. 



By these empirical techniques, the survival of fish 

 past early critical periods has ranged in recent experi- 

 ments mostly from 30 to 50 percent of the original stock 

 of eggs. Occasionally, batches of several hundred fish 

 were reared through metamorphosis to thesubadult stage 

 with considerably higher survival rates than this. 



Population Dynamics Program 



This program has four projects: a continuing com- 

 mitment to the resource surveys of this region within the 

 framework of CalCOFI; the BCF commitments to coop- 

 erative collection and analysis of data on the dynamics of 

 harvested fish populations in the California Current; anal- 

 ysis of the racial structure of some of the important 

 commercial fish species in the California fishery; and the 

 analysis of historical data on zooplankton abundance by 

 computer methods and use of this analysis to increase 

 the efficiency of future surveys, and to develop new and 

 more efficient survey methods. 



CALIFORNIA CURRENT RESOURCE SURVEYS 



This project is designed to analyze the flow of in- 

 formation which is derived from the BCF participation in 

 CalCOFI, especially the data on eggs and larvae of com- 

 mercially valuable fishes, together with the lai-vae of as- 

 sociated fishes. 



The samples are collected in cooperation with SIO 

 (Marine Life Resources Program). Generally, the staff 

 for biological collections are furnished by the Center and 

 those who collect physical data are furnished by SIO. 



Primary sorting of the samples to obtain the num- 

 ber and length frequency of the larvae of sardine and 

 anchovy, together with the number of unclassified eggs 

 and larvae is immediately undertaken ashore in the Cen- 

 ter. Subsequently, unclassified larvae are identified to 

 family, genus, or species. This process has been com- 

 pleted through the end of the samples for U)66, and 

 only samples from one or two cruises in subsequent 

 years remain to be processed. The product of this a- 

 nalysis is an estimate of the numbers of spawning adults 

 in the CalCOFI grid, of Pacific sardine, northern anchovy. 

 Pacific mackerel, jack mackerel, and Pacific hake (Mer 

 lucciiis productusj. 



During the past year. J.R. Zweifel has coded for 

 automatic data processing all of the biological and many 

 of the physical data, including those taken on monthly 

 CalCOFI cruises from 1 1^5 1-60. This work furnishes an 

 excellent data base (though it will be added to subse- 

 quently for 1961-66) for analyses of spawning seasons 

 for each species, and of yearly anomalies from the long- 

 term average. 



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