INTRODUCTION 



In the first paper of this seriesi' , Sette, 1914-3, has stated that 

 a major requisite in the program of pilchard research is the measure- 

 ment of recruitment. This can bo obtained most directly from a quan- 

 titative sampling of pilchard egf^s and larvae at sea in and around the 

 region knovm to be the chief spavming grounds. Determinations of the 

 amount of spavming require the integration (over both time and space) 

 of the quantitative samples of eggs. To accomplish this necessitates 

 knowing as exactly as possible the age of any particular stage of de- 

 velopment, as well as the number of days of spawning represented in each 

 collection. Since rate of development is strongly influenced by tem- 

 perature, it is necessarj"- to know the relation between these two vari- 

 ables to get a precise method of determining the age of eggs in all 

 samples . 



So far it has been unfeasible to procure live spawning pilchards 

 for artificial fertilization and propagation of eggs. Fishermen rarely 

 catch ripe, spawning pilchards, and vre have lacked facilities wherewith 

 we could attempt to catch them. Although eggs newly spawned were col- 

 lected in the plankton samples, constant temperature apparatus was not 

 available to permit hatching experiments under controlled conditions . 

 Hence, it has been necessaiy to approach the problem analytically by cor- 

 relating temperature data collected in the field vvith the probable length 

 of time particular stages in the samples had been developing. 



The writer is indebted to Oscar Elton Sette, in charge of the South 

 Pacific Investigations, for continuous aid and advice throughout the 

 development of this problem, to Dr. L. A. Walford for valuable help in 

 the preparation of the manuscript, and to Elizabeth Vaughan for assist- 

 ance and suggestions in the mathematical treatment. The plankton hauls 

 for the most part were made by the author and other members of the South 

 Pacific Fisher;^' Investigation staff of the Service, vfhile the occano- 

 graphic observations, of which the temperatures-data of this paper were 

 a part, were the responsibility of the Scripps Institution of Oceano- 

 graphy staff. Sorting of the plankton collections was accomplished with 

 the assistance of employees from Works Progress Administration projects 

 Nos. 10917 and 65-2-08-286. 



COLLECTION OF UAT^nlAL 



The plankton collections on which this paper is based were made 

 during the pilchard spasming surveys of 19hO and 19U1, conducted by the 

 South Pacific Invest j.gations of the Fish and Vildlife Service in conjunc- 

 tion with the Scripps Institution of Oceanography from the research 



i/oscar Elton 3ette. Studies on the Pacific Pilchard or Sardine (Sardinops 



caerulea). I - Structure of a Program for Pacific Pilchard (or Sardine) 

 Research. Special Scientific Report No. 19. 



133 



