PARRISH ET AL.: REGIONAL VARIATIONS IN NORTHERN ANCHOVY 



southern stock does extend into this region. The 

 most northerly trawl sample which could be iden- 

 tified, by size at age, as southern stock was a June 

 1971 sample taken at lat. 30.3°N. Southern and cen- 

 tral stock anchovies broadly overlap in the Sebas- 

 tian Viscaino Bay region; however, the region is 

 occupied principally by the southern stock in the 

 summer and by the central stock in the fall and 

 winter. The Southern Baja California region is 

 dominated by the southern stock; however, central 

 stock anchovies, as identified by size at age, were 

 taken as far south as lat. 26.5°N in November 1967. 

 The fact that the central stock is the farthest south 

 in winter and the southern stock the farthest north 

 in summer suggests that the separation of the stocks 

 is aided by different environmental preferences, 

 possibly temperature 



The Central California region is an area of overlap 

 between the northern and central anchovy stocks. 

 In addition, as previously mentioned (Parrish foot- 

 note 3), a fall spawning stock may occur in central 

 California and the offshore areas of the Southern 

 California Bight. Vrooman et al. (1981) did not have 

 any samples south of Monterey in central Califor- 

 nia or from the offshore and northern areas of the 

 Southern California Bight. Samples from these areas 

 may consist of a mixture of different stocks with dif- 

 ferent spawning seasons. Our assumption of a 

 February birth month in these areas must therefore 

 be evaluated. 



Regression Analysis 



Growth in length of anchovies in the size range 

 sampled by the Sea Survey Program (i.&, 40-180 mm 

 SL) can be divided into two phases. The early, 

 juvenile phase extends until the fish are about 1 yr 

 old. Methot (1981) found that in the Southern 

 California Bight juvenile growth averages about 9 

 mm/mo, and it is at a maximum when the fish are 

 between 40 and 50 mm SL. The second, adult phase 

 extends from a little over 1 yr old until death. Growth 

 during this phase is more than an order of magni- 

 tude less than the early phase (i.e, 0.48-0.69 mm/mo). 

 Examination of the age-length relationships (Figs. 

 3, 4) in the central stock shows that growth in the 

 adult phase is essentially linear. Therefore, we used 

 linear regressions to compare growth of anchovies 

 from different regions. These analyses included 

 only fish of IV2 yr of age and older. This model has 

 several advantages for comparing the growth dur- 

 ing the two phases described above. By limiting the 

 model to the linear segment of the age-length rela- 

 tionships, the slopes of the regressions can be used 



to compare the regional variations in growth rate 

 during the adult phase Another advantage is that 

 the expected length at 172 yr of age can be used to 

 compare regional variation in growth during the 

 juvenile phase 



Juvenile Growth 



In the area occupied by the central stock, growth 

 during the juvenile phase shows considerable varia- 

 tion among regions. There were significant dif- 

 ferences in growth to age IV2. Fastest growth oc- 

 curred in the north, and the slowest was in the south 

 (Tkble 2, Fig. 5). Mean standard length at IV2 yr of 

 age was 123.6 mm in the Central California region, 

 113.4 mm in the San Pedro Channel region, and 

 103.6 mm in the Cape San Quentin region. The three 

 southernmost Baja California regions contain mix- 

 tures of the central and southern stocks; therefore, 

 data from these regions were divided into central 

 and southern stock sets, based on length and month, 

 for the analyses. In contrast to those of the central 

 stock, anchovies of the southern stock attain only 

 91.8 mm by age IV2. Within the Southern Califor- 

 nia Bight there is also an inshore-offshore gradient, 

 with faster juvenile growth in the offshore regions 

 and slower grov^th in the inshore regions (i.e, lengths 

 at age IV2 in the Coronado Escarpment, Catalina 

 Basin, and Tanner and Cortez Banks regions were 

 110.5, 116.4, and 119.2 mm respectively). 



An analysis of covariance showed that the dif- 

 ferences in size at age IV2 are not significantly dif- 

 ferent {a = 0.01) in two pairs of regions. The San 

 Nicolas region (120.4 mm at age IV2) and the Ikn- 

 ner and Cortez Banks region (119.2 mm) are the first 

 pair, and the Catalina Basin region (116.4 mm) and 

 the Santa Barbara Channel region (116.2 mm) are 

 the second pair. In all other pairs of regions, size at 

 age IV2 is significantly different at the a = 0.0001 

 level. 



Adult Growth 



The regressions demonstrate that growth during 

 the adult phase is relatively constant between the 

 different regions occupied by the central stock, with 

 slopes varying from a low of about 6 mm/yr to a high 

 of about 8 mm/yr (Ikble 2). In contrast, anchovies 

 of the southern stock have essentially no adult 

 growth after age IV2 (i.e, slope = 0.07 mm/yr). 



Although the differences in adult growth between 

 regions is not large, there are statistically significant 

 differences (Tkble 3). The San Nicolas region and the 

 Tknner and Cortez Banks region have adult growth 



489 



