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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



extent of season-to-season variability in inter- 

 change of northern and southern populations are 

 as yet not determined. 



Possibilities of inshore-offshore migrations of 

 pilchard are in the main unexplored and, short of 

 the use of radioactive markers, may be difficult 

 to determine. Hart (1943a, p. 178), however, 

 records tagged fish moving into inlets on the west 

 coast of Vancouver Island and remaining there 

 throughout the winter. Such winter fish, ac- 

 cording to Hart, "are occasionally captured during 

 the winter herring fishing season and . . . they 

 sometimes provide early in-shore fishing before 

 the main pilchard shoals approach the Vancouver 

 Island coast in the summer." 



North-south variation in growth characteristics 



The variation in growl li of pilchard from north 

 to south may prove to be a physiological char- 

 acteristic of cliiial significance. The study of 

 intraspecific clines in fishes is, of course, compli- 

 cated by what Mayr (1944, p. 135) terms the 

 "strong and only rather recently appreciated 

 phenotypical plasticity of many species." It 

 seems likely that the greater size of fish in northern 

 waters is not entirely explained by northern 

 migration of the larger individuals of each year 

 group. These northern pilchard may represent a 

 separate stock grown to larger sizes rather than 

 (inly a sorting out of larger fish from a whole 

 coastal population. It may be that such growth 

 differences from north to south can be explained in 

 part by geographical gradients in environmental 

 factors associated with gradients in morphological 

 and physiological characters, or clines, within 

 the range of a species. 



It seems probable from existing evidence on 

 growth characteristics of the fish in different geo- 

 graphical regions that there may be season-to- 

 season fluctuations in the size and the location of 

 optimum living areas associated with fluctuations 

 in marine climate. Such fluctuations may largely 

 determine what part of the sardine population 

 will be available for capture in each area. Illus- 

 trative of between-season shifts in populations are 

 the apparently greater deviations in mean ob- 

 served lengths than in mean calculated lengths of 

 a year class from its rectilinear transformation. 

 But it also seems evident from back calculated 

 lengths that there is, lor a given year class, a per- 

 sistent dine in growth characteristics from north 



to south, and that populations, although fluctu- 

 ating in distribution from season to season and 

 somewhat migrant, may be more discrete and 

 limited latitudinally than has been supposed from 

 the evidence of vertebral counts (Clark 1936, 

 1947) and tagging (Hart 1943a; Clark and 

 Jaussen 1945). 



McHugh (1950) has reported on latitudinal 

 variation in three species of clupeoids of the North 

 Pacific. Parallel gradients in hydrographie and 

 meristic characters and consequent homogeneity 

 or heterogeneity of populations with respect to 

 certain characters are discussed. For the north- 

 ern anchovy (JEngravlis mordax) and Pacific sar- 

 dine, McHugh found clines in anal fin-ray counts 

 and significant heterogeneity among several pop- 

 ulations. He notes close parallelism in meristic 

 counts of anal fin rays in anchovy and sardines 

 and likewise in vertebral counts of both species. 

 From his more complete study of meristic char- 

 acters in anchovy, McHugh concludes (p. 58) that 

 "clines in numbers of dorsal, anal and pectoral 

 fin rays are in the opposite direction to that 

 shown for gill-rakers, and all four fail to corre- 

 spond with the distribution of mean vertebral 

 number." 



McHugh considers it probable that in the Pa- 

 cific Northwest the fixation period for sardine 

 fin-ray counts occurs during a period of warmer 

 water temperatures, while in southern California 

 water temperatures average lower at this period 

 of development. Thus the usual inverse relation 

 between meristic count and temperature follows 

 for counts of fin rays as well as of gill rakers, and 

 to a lesser degree of vertebrae. 



Lack of significant differences in vertebral 

 counts between samples of sardines from British 

 Columbia to southern California (Clark 1936, 

 1947), and the heterogeneity in populations ac- 

 cording to fin-ray counts, McHugh attributes to 

 close dependence of each meristic character on 

 coexistent physical factors in the environment at 

 the time of fixation of the character. Since spawn- 

 ing occurs within a rather narrow temperature 

 range, phenotypic variation could likewise be nar- 

 row for a character, such as vertebral number, 

 with an early fixation period, whereas with a later, 

 perhaps longer, fixation period there could be 

 greater concomitant variability in environmental 

 factors and heterogeneity of populations as indi- 

 cated by these other meristic characters. 



