feature of the collapse of the sardine fishery was 

 its north-to-south progression, which owed 

 greatly to the interaction of underlying life his- 

 tory variation (in particular, steep north-south 

 clines in size-at-age, age of first reproduction, 

 maximum size, and the schedule of natural mor- 

 tality), geographical shifts in fishing pressure, 

 and natural between-year variation in recruit- 

 ment (Murphy 1966; Radovich 1982). That life 

 history variation was built upon genetic differ- 

 ences among geographic populations, however, 

 now appears unlikely from the results of our 

 study. 



The single, most obvious component of mor- 

 phological variation in Pacific sardines today is a 

 geographic cHne in size-at-age that is as steep 

 and as large as that seen in historical populations 

 (Fig. 2). In the past, such differences were used 

 by several authors to infer the existence of ge- 

 netically distinct subpopulations, yet the differ- 

 ences have been reestablished in genetically 

 homogeneous, contemporary populations within 

 just a few generations. This imphes that rapid 

 differentiation of growth rate among geographic 

 populations — probably together with differentia- 

 tion of correlated life history features such as 

 age at first reproduction, maximum size, and 

 age-specific mortality (Clark and Marr 1955; 

 Blaxter and Hunter 1982) — is largely environ- 

 mentally, and not genetically, determined. This 

 is not to say that there are not genes that deter- 

 mine life history traits; but variation of these 

 genes cannot be responsible for geogi'aphic var- 

 iation in life history. The genotype of the Pacific 

 sardine must instead provide for remarkable 

 plasticity in hfe history phenotype. 



One must now be skeptical of the interpreta- 

 tion that life history differences among historical 

 sardine populations were conditioned by genetic 

 differences among subpopulations or races. The 

 question of which sardine stock is now recover- 

 ing is moot. More importantly, it appears that 

 information on the biology of sardine populations 

 prior to the collapse of the fishery can safely be 

 used for area-specific fisheries models of the re- 

 covering stocks. 



ACKNOWLEDGMENTS 



The authors dedicate this paper to the mem- 

 ory of Dr. Reuben Lasker in appreciation for his 

 encouragement to make these studies, for his 

 advocacy of our proposals, and for his unfaihng, 

 forthright, and constructive criticism of our 

 methods and conclusions. The authors thank P. 



FISHERY BULLETIN; VOL. 87, NO. 3, 1989 



Woods, R. H. Parrish, P. Wolf, K. Worcester, 

 Giovanni Malagrino, W. Borgeson, and J. 

 Estrada for help in obtaining Pacific sardines; we 

 thank R. D. Methot for collecting the northern 

 anchovy used in the study. This research was 

 funded by a grant (R/F-98) from the Cahfornia 

 Sea Grant College Program. 



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