POPULATION HETEROGENEITY IN PACIFIC PILCHARD 



221 



less successful and primarily a southern year class. 4 

 The 1942 class was of about average strength and 

 the San Pedro-Pacific coast ratio indicated prob- 

 able northern origin. The year classes 194)5, 

 1944, and 1945 were below average strength and 

 showed early dominance at San Pedro as com- 

 pared with the rest of the coast. The 1946 year 

 class was above average strength and the San 

 Pedro-Pacific const ratio was below 1.0 at 1-ring, 

 although comparatively in greater numbers as 

 2-ring at S;m Pedro. The 1947 class appears the 

 most successful of any year class since that of 

 1939, and it shows a low San Pedro-Pacific coast 

 ratio. 



From these data I lie existence of southern and 

 northern year classes seems indicated. Early 

 northern strength, or a low ratio, may prove indic- 

 ative of a widespread spawning and a relatively 

 successful year class. There also arc indications 

 that a strong southern year class, such as those of 

 1941, 1946, and probably L948, can make such 

 significant contributions to southern catches that 

 their year-class strength when measured by num- 

 bers caught along the whole coast at 3-ring still 

 can be considerable. It is nevertheless only 

 those year classes 194:!, 1944, and 1945 which 

 appear predominantly southern, by these criteria, 

 that so far have been much below normal strength. 



The San Pedro to Pacific coast ratios at 1-ring 

 may be a better measure of relative year-class 

 strength by region than ratios at 2-ring. There 

 are apparent wide variations in availability, as 

 well as in recruitment, of pilchard at I -ring -is 

 shown in total numbers of this age class caught 

 during each season at each port (cf. Felin and 

 Phillips L948: Mosher el al. 1949: Felin el al. 

 1949; Felin el al. 1950; Felin et at 1951). Such 

 wide variations are likely to be associated with 

 the origins of each year class. By the linic sar- 

 dines have reached 2-ring they may be more 

 widely dispersed and their origins more obscure. 

 Hart (1943 a, p. 174), for example, noted that two 



' William T. Miller (ms.) round thai temperatur nditions in the spring 



of 1941 were unusually warm in the area oil Lower California during February 

 and March, and that according to r niied stales 1 1 \ drographic Office records, 

 water temperatures were higher than those normally associated with pilchard 

 spawning. His charts simtest thai during this season temperatures ravoi 

 able for spawning were restricted both in space and time, namely to the area 

 off southern California. He contrasted tin- 1941 season with the 19:19, an 

 unusually cold spring, and showed that during the latter season temperatures 

 off Lower California were fayorable for spawning oyer a wide area in Febru- 

 ary, March, and April Water temperatures suitable for the widespread 

 northern spawning known to have taken place in 1939 were also recorded. 

 The nlative scarcity of fish of the 1941 year class in northern catches might 

 thus he attributed to contraction of areas and time of spawning. 



fish, probably of the 1939 year class, tagged at 

 Monterey by the California Bureau of Marine 

 Fisheries, were taken off the Canadian coast 

 early in 1941, presumably at the 2-ring stage. 



In general, the assumption that 1- and 2-ring 

 fish have not traveled great distances is sub- 

 stantiated by the behavior of tagged sardines of 

 these approximate sizes. Data from Janssen 

 (1938) and Clark and Janssen (1945) show that 

 recoveries to the north of fish from the southern 

 California tagging area are at first of larger sizes 

 than commonly would occur in the 1- and 2-ring 

 age classes. It is also evident from Phillips' (1948, 

 p. 7) average length-on-time growth curves for the 

 Pacific Northwest, central California, and southern 

 California, that for the 6-season period (somewhat 

 subsequent to the tagging data) the mean ob- 

 served lengths at 1- and 2-ring tire greater for 

 San Pedro fish than for those caught in the 

 Pacific Northwest. In central California, 1-ring 

 fish average smaller than those in the other two 

 areas. At 2-ring. central California sardines 

 begin to exceed the sizes at San Pedro. At 3-ring 

 I he si/.cs of Pacific Northwest pilchard begin to 

 exceed those caught in the other two areas. 

 These data indicate that few large 1- and 2-ring 

 fish have left the southern California area. 



Further evidence that the larger 1-ring and 2- 

 ring sardines have not migrated far from the 

 southern grounds is provided by calculated length 

 data (table 4). At 1-ring the mean calculated 

 first growth increment, /,, is greater at San Pedro 

 than at Monterey for all the year classes over the 

 9-year period of study. At 2-ring, for nearly all 

 year classes the /, still is greater in the southern 

 area. By the time the year classes have reached 

 3-ring (he situation has reversed and the calculated 

 first growth increments are nearly all greater in 

 central California, indicating a strong influx 

 of soul hern fish with large 7, into the area. For 

 nearly all year classes at 4- and 5-rings of age the 

 average calculated first growth increment 

 continues to be greater at Monterey than at 

 San Pedro. 



Ronquillo (1949, p. 12) found statistically sig- 

 nificant difference in mean observed lengths of 0- 

 and 1-ring fish in San Pedro and Monterey and 

 concluded that "fish reared in these two areas do 

 not intermingle at this age." Since the commercial 

 fishery is carried on in the winter off California 

 when growth is minimal and the first ring will soon 



