PRELIMINARY STATISTICAL REPORT 



ON THE 



OCCURRENCE OF MARINE COPEPODA IN THE 

 PLANKTON AT LA JOLLA, CALIFORNIA 



BY 



CALVIN O. E8TERLY 



(Contribution from the Scripps Institution for Biological Research, La Jolla, California) 



This paper summarizes some of the results of two years of plankton 

 collecting from the pier at the Scripps Institution for Biological 

 Research of the University of California at La Jolla, California. The 

 series consists of 3471 hauls extending from September 1, 1916, through 

 August, 1917. All hauls were made at the surface of the water, using 

 a conical plankton net of either No. 12 or No. 9 silk bolting cloth. 

 The mouth of the net was fourteen inches in diameter and the length 

 of the filtering portion about thirty-four inches. In making the 

 collections the net was tied to a cord and towed from the end of a 

 pole held over the edge of the pier. The distance it was hauled was 

 about 80 feet, beginning about 100 feet from the end of the pier. 

 A wide-mouthed four-ounce bottle was tied into the peak of the net 

 so that upon draining the net the catch was swept into the bottle. 



Hauls were taken six times in twenty-four hours: at 8 a.m., noon, 

 4 p.m., 8 p.m., midnight, and 4 a.m. In very rough weather the collect- 

 ing was omitted, and it was agreed that there need be no towing 

 between 4 p.m. on Saturday and 8 p.m. on Sunday. Occasionally 

 emergencies arose that prevented hauling, but on the whole the 

 program was adhered to very well. 



The author is responsible for the counting and identification of 

 the Copepoda. The method of counting that was used throughout 

 was, of course, one of sampling. The fluid in the bottle was decanted 

 imtil a small amount, merely enough to contain the catch, remained. 

 This residue was poured into a watch dish and the contents con- 

 centrated by shaking the dish rapidly back and forth without lifting 

 it from the table. It is possible to gather quickly into a compact 

 mass objects as relatively heavy as copepods. If the haul was a small 

 one copepods of the size of Acartia and larger were all counted. But 

 in most cases there were too many to permit of counting them all ; so 



