Genetic and Morphometric Variation in the Pacific Sardine, Sardinops sagax caerulea: Comparisons and Contrasts with Historical Data and with Variability in the Northern Anchovy, Engraulis mordax

Pacific sardines from five widely separated localities are found to have little genetic variation both within and between populations. Of the 32 allozyme-coding loci examined from a total of 149 fish. the proportions that are polymorphic within a population (P) range from 7% to 27% with a mean of 12%. Average proportions of heterozygous individuals per locus (He) range from 0.5% to 1.6% with a mean of 1.0% over the five populations. Pacific sardine populations are virtually genetically identical at the presumptive gene loci examined. For each locus that is polymorphic in more than one population, the same rare variant allele is shared at about the same frequency, suggesting strongly that there has been gene flow throughout the present range of the species. These results contrast with substantial genetic variation detected within and between northern anchovy populations from the California central stock (average P = 40%. average He = 7.5%) and with the significantly higher levels of genetic variation reported for other marine clupeoids. Despite a low level of genetic variation. the Pacific sardine shows a north-south cline in size-at-age that is as steep and as large as that seen in historical. precollapse populations. In the past, such differences were interpreted as evidence of genetically distinct subpopulations. Our results imply that rapid differentiation of growth rate among geographic populations, probably together with differentiation ofcorrelated life history traits. is largely environmentally, and not genetically, determined. It appears that biological data from historical populations can safely be used for area-specific fisheries models of the recovering sardine stocks in California. A variety of studies have suggested that. prior to its collapse in abundance, the Pacific sardine, Dennis Hedgecock, Elmarie S. Hutchinson, Frederic L. Sly, Keith Nelson: Aquaculture and Fisheries Program, University of California, Davis, Bodega Marine Laboratory. Bodega Bay, CA 94923. Li Gang, South China Sea Institute of Oceanology. Academia Sinica, 164 Xin Gang-Xi Road, Guangzhou. People's Republic of China. Manuscript accepted February 1989. Fishery Bulletin, U.S. 87:653-671. Sardinops sagax wendea. comprised two or more distinct subpopulations (morphometry and meristics: Hubbs 1925; Clark 1936, 1947; McHugh 1950; growth: Phillips 1948; Felin 1954; Clark and Marl' 1955; Radovich 1962, 1982; movements of tagged fish: Clark and Janssen 1945; Clark and Marl' 1955; spatiotemporal distribution of spawning: Ahlstrom 1954, 1959; erythrocyte antigens: Sprague and Vrooman 1962; Vrooman 1964; reviews by Marl' 1957; Radovich 1982). Population structure likely played a role in the collapse of the fishery, perhaps directly, by virtue of differences among subpopulations in life histOl'y and resilience to fishing pressure (Wisner 1961; Murphy 1966; Radovich 1982) and more celtainly, indirectly, by contributing to overestimations of stock size in the waning years of the fishery (MacCall 1979). With the return of substantial numbers of Pacific sardines to the California Current in recent years and the lifting of the fishing moratorium (Wolf et al. 1987) has come interest in management questions such as wh-ich sardine has recovered and what life history characteristics and yields can be expected (MacCaIl1986). We have made studies of protein and morphological variation in the Pacific sardine to shed light on such questions. Electrophoretic separation of proteins followed by chemical staining to reveal the locations of proteins or specific enzymes allows inferences to be made concerning variation in the genes encoding these proteins. This in turn provides a description, useful for management, of the genetic structures of exploited fish populations (see Ryman and Utter 1987). Several clupeoids, including the northern anchovy, EngrauHs 1norda.l=, which co-occurs with the Pacific sardine in the California Current, have been shown to harbor considerable stores of electrophoretically detectable genetic variability <Hedgecock and Li 1983; Table 8). In this paper, we compare protein and allozyme variation in samples of Pacific sardines collected