PARRISH ET AL.: REGIONAL VARIATIONS IN NORTHERN ANCHOVY 



more extended spawning season with a broad peak 

 from February to April, and there is some spawn- 

 ing all year in the central stock region. It is not yet 

 known if the anchovies that spawn in central and 

 southern California during the summer and fall are 

 from the central stock, northern stock, or a possi- 

 ble fall spawning stock. If the anchovies in this 

 region are predominatly from the central stock, the 

 relatively high juvenile growth in central California 

 and the offshore portion of the Bight might be due 

 to a favorable feeding environment. Offshore por- 

 tions of the Southern California Bight have been 

 shown to have considerably more plankton and 

 nutrients than the inshore portions (Reid et al. 1958; 

 Owen 1980). If the anchovies in the area occupied 

 by the central stock have a large component that are 

 not central stock, the increased juvenile growrth could 

 be due to the genetic differences, due to environmen- 

 tal differences, or caused by the assumption of a 

 February birth month. At our "assumed" age of IV2 

 yr, an anchovy spawned in the fall would be about 

 6 mo older than the "normal" central stock anchovy. 

 If the growth that occurred during these additional 

 5 mo was at the normal adult rate (i.e, 0.48-0.69 

 mm/mo), there would be only a 2-4 mm difference 

 in the size of the two fish. However, the difference 

 in mean length between lV2-yr-old anchovies in the 

 central California and Cape San Quentin regions is 

 20 mm. If, however, growth during the 5 mo is even 

 one-half of the average juvenile rate (i.e, 9 mm/mo) 

 the difference in size at "IV2" yr could be achieved. 



CONCLUSION 



The interpretation of regional variations in the 

 growth and age composition of northern anchovies 

 in the area between central California and central 

 Baja California and the implications of this study for 

 fisheries management are dependent upon the stock 

 structure of the anchovies in the area. 



If a significant proportion of these fish are not 

 from the central stock, this study suggests the 

 following: 



1. The observed regional variation in age composi- 

 tion may be the result of mixtures of stocks with 

 different mortality rates. 



2. The juvenile growth rate of anchovies in the cen- 

 tral stock is lower than that of anchovies from 

 the northern stock(s). The reason for this lower 

 growth rate could be either genetic, environ- 

 mental, or dependent upon the seasonality of 

 spawning. 



3. The southern California and Mexican fisheries 



are based on different stock mixtures, and thus 

 the interactions between these fisheries would 

 not be as great as they would be if both were 

 based entirely on the same stock. 



If essentially all of these anchovies are from the 

 central stock, this study suggests the following: 



1. The offshore regions of the Southern California 

 Bight contain a disproportionate share of the 

 adult anchovies; however, recruitment does not 

 occur here to any significant extent. 



2. Recruitment occurs largely in shallow water 

 along the coast, and the northern Baja Califor- 

 nia region has the largest percentage share of 

 young-of-the-year anchovies. 



3. Larvae and juveniles recruited from the offshore 

 regions of the Southern California Bight tend 

 to move or be advected south and inshore 



4. The relatively high juvenile growth rates in cen- 

 tral California and the offshore regions of the 

 Southern California Bight are due to favorable 

 environmental conditions. 



5. As they grow older anchovies tend to move, or 

 be advected, north and offshore 



6. Mixing of adults is not complete; otherwise 

 length at age and age composition would be the 

 same everywhere 



7. Due to the inferred tendency for recruitment to 

 occur in the south, an extensive fishery on the 

 central stock would reduce the proportion of 

 older anchovies and result in fewer older an- 

 chovies in the northern and offshore areas. 



8. The combination of the large Mexican fishery, 

 which has been associated with a reduction in 

 the proportion of older anchovies (Mais 1982), 

 and the continued closure of the nearshore areas 

 where younger fish are concentrated will severe- 

 ly impact the California fishery. 



ACKNOWLEDGMENTS 



We are grateful to Roy Mendelssohn, Alec Mac- 

 Call, Janet Mason, and Rick Methot for their com- 

 ments and editorial assistance In addition we wish 

 to thank Susie Myers for her help in completing the 

 manuscript. 



LITERATURE CITED 



Ahlstrom, E. H. 



1966. Distribution and abundance of sardine and anchovy lar- 

 vae in the California Current Region off California and Baja 

 California, 1951-64: A summary. U.S. Fish Wildl. Serv., Spec 

 Sci. Rep.-Fish. 534, 71 p. 



495 



