BUTLER: NORTHERN ANCHOVY GROWTH IN THE CALIFORNIA CURRENT 



anchovies during 1983 may be a direct result of 

 reduced food availability at the same time that 

 the rapidly growing juveniles experienced 

 higher metabolic rates due to the elevated en- 

 vironmental temperatures. Zooplankton vol- 

 umes on CalCOFI line 90 (hne 90 intersects the 

 coast at lat 33°29.9'N, long. 117°44.4'W and pro- 

 ceeds seaward on a bearing 240° clockwise from 

 North) were lower than the 95% confidence limit 

 of the 30 year CalCOFI time series (McGowan 

 1985). 



Growth rates were not, however, depressed 

 over the entire early life history. The growth 

 rates of larval stages (5-35 mm) were not signif- 

 icantly different between the two years 1982-83 

 (Figs. 3, 4). Growth rates in 1983 were reduced 

 in the early juvenile stage, and in particular 

 after 40 mm, compared with gi-owth rates in 

 1980. 



Thus food was not growth Hmiting until the 

 fish reached a certain size. As fish larvae gi-ow, 

 the ration necessary to sustain growth increases. 

 Since the density of food particles decreases with 

 size (Sheldon and Parsons 1967; Sheldon et al. 

 1972), at some stage food must become growth 

 limiting. Based on this analysis, food-limited 

 growth is unlikely in anchovies <40 mm during 

 conditions that existed in the Southern Cali- 

 fornia Bight in 1983, and unlikely in anchovies 

 <65 mm during "normal" years such as 1980. 



The similarity of back-calculated larval gi'owth 

 rates between years may be a result of the inter- 

 action of gi'owth and mortality. A wide range of 

 growth rates are possible at this stage (Hunter 

 1980), but variable growth rates are not ob- 

 served in the field. Mortality of slow-growing 

 individuals may reduce the range of growth 

 rates in survivors to metamorphosis. 



While the 1957-58 El Nino had a dramatic 

 effect on northern anchovy recruitment in 1958, 

 the numbers of fish in the 1983 and 1984 year 

 classes were not appreciably lower than the pre- 

 vious years (Methot 1988). Thus, although the 

 juvenile period was prolonged in 1983, recruit- 

 ment was not affected. The major effect of El 

 Nino on the anchovy population was to reduce 

 the size of recruits as well as perhaps the size of 

 adults and the reproductive potential of the 1983 

 and 1984 cohorts. 



ACKNOWLEDGMENTS 



I am indebted to Dr. Reuben Lasker (National 

 Marine Fisheries Service, NOAA) for many 

 thought provoking discussions. Ken Mais (Cah- 



fornia Department of Fish and Game) provided 

 samples of juvenile anchovy from survey cruises. 

 Susan Longinotti (University of California at 

 San Diego) collected much of the data analyzed 

 here. John R. Hunter, Paul E. Smith, and 

 Robert W. Owen of the National Marine Fish- 

 eries Service and William H. Bayliff of the 

 Inter-American Tropical Tuna Commission 

 made many useful comments on the manuscript. 



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