THE SUBPOPULATION PROBLEM IN THE PACIFIC SARDINE 

 SARDINOPS CAERULEA 



By 

 John C . Marr 



1/ 



The fishery for the Pacific sardine 

 (Sardinops caerulea) is one of the most com - 

 pletely documented in the world and, similarly, 

 knowledge of the biology of the sardine is at 

 least as complete as it is for any other marine 

 fish. Information arising from a long period of 

 study, plus greatly intensified studies in recent 

 years, now makes it possible to ask intelligent 

 questions about the number and location of 

 sardine subpopulations and to suggest critical 

 methods of examining these questions . The in- 

 formation now at hand, the questions asked and 

 methods of seeking answers to them will be re - 

 viewed in the following sections . 



The introductory section of the first paper 

 in this collection is pertinent here and need not 

 be repeated. Suffice it to say that I use the 

 term "subpopulation" in the sense that it is a 

 self-sustaining unit; subpopulations segregate 

 at spawning time and their characteristics are 

 heritable . 



REVIEW OF PRESENT KNOWLEDGE 



Many kinds of information bearing directly 

 or indirectly on the subpopulation problem have 

 accumulated over the years. These are categor- 

 ized below . 



Catch data and other information: Twenty 

 years ago it was generally believed that there 

 was only one major group of sardines, which 

 was produced in the southern part of its range 

 and, with increasing size (or age), performed 

 successively longer feeding migrations to the 

 north in the spring and summer and spawning 

 migrations to the south in the fall and winter. 

 (The sardines off the west coast of southern 

 Lower California and in the Gulf of California 

 1/ Chief, South Pacific Fishery Investigations, 

 U.S. Fish and Wildlife Service, 

 P.O. Box 271, La Jolla, California. 



were considered to be of uncertain relationship 

 to the northern group.) This view was summar- 

 ized by Clark (1935:5-6): 



"The changes in size of fish from the 

 smaller, fall fish to the larger, winter fish re- 

 sult from the movements of sardines up and 

 down the California coast. Young fish reared 

 on the nursery grounds of southern California 

 and northern Lower California work northward 

 during their first and second years. The spring 

 bait fishery at San Diego appears to be com- 

 posed in part of fish which have been reared at 

 San Diego and in part of fish which have been 

 reared to the southward. At approximately two 

 years of age (7-1/2 to 9-1/2 inches in length) 

 sardines of any year class are first taken in im- 

 portant numbers in the San Pedro fall fishery. 

 Some fish of this size and age also appear at 

 Monterey in the fall of the same year but the 

 majority does not go as far north as Monterey 

 until one year later. These fish are adolescent 

 and in general exhibit the same behavior as do 

 the adult sardines . During the summer of each 

 succeeding year a given year class moves a 

 little farther north along the California coast and 

 makes a return journey to the south during the 

 fall and winter. The more extended northward 

 movement each succeeding summer causes a 

 correspondingly later appearance of the older 

 fish at any given point on the southward journey. 

 The larger and older fish do not appear off 

 Monterey and San Pedro until the winter months. 

 Their return to Monterey occurs about a month 

 earlier than to San Pedro. Just how far north 

 any year class moves in each succeeding summer 

 we have not learned as yet, but all evidence at 

 hand indicates that the largest and oldest fish 

 reach British Columbia sometime between July 

 and September. Perhaps these fish constitute 

 stragglers from the main population but more 

 probably the maiority of them again returns to 

 southern California waters in the spring to 



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