FISHERY BULLETIN; VOL. 87, NO. 3, 1989 



ment was 104%. Only two life history param- 

 eters varied more than the spawning biomass 

 (35%): adult density per unit area (47%) and egg 

 mortality (38%) (Smith and Moser 1988). While 

 cannibalism is sufficiently important as a source 

 of egg mortality to control the size of populations 

 like sardine and anchovy over the long term, it is 

 unlikely that the interannual variation in rates of 

 mortality due to cannibalism are sufficient to 

 cause major recruitment variations. One would 

 suspect that variability in egg mortality rate 

 could arise from the 70% of egg mortality not due 

 to cannibalism. Off California, Theilacker (1988) 

 has estimated that the rate of northern anchovy 

 egg consumption by juvenile and adult euphau- 

 siids may account for 28% of the egg mortality. 

 Other influences on recruitment could arise from 

 copepod predation on yolk-sac larvae (Lillellund 

 and Lasker 1971) and predation of Pacific 

 mackerel on juveniles (Methot 1986'"). 



To manage variable stocks hke the sardine and 

 anchovy it may be sufficient to monitor the age 

 structure of the catch and the production and 

 survival of the embryonic stage (Methot and Lo 

 1987^). A decrease in the number of older, highly 

 fecund, spawning age classes will decrease effec- 

 tive population fecundity. In filter feeders like 

 sardine and anchovy, cannibalism by younger 

 age classes may lower the survival of eggs. 

 Thus, merely by monitoring age structure and 

 egg survival one can project when large, un- 

 usually successful year classes are possible. New 

 techniques for monitoring juvenile abundance 

 and growth will be required when a sardine or 

 anchovy fishery becomes so intensive that an 

 early recruitment prediction is necessary. 



ACKNOWLEDGMENTS 



The late Dr. Reuben Lasker was the mentor 

 and enthusiast for work on population assess- 

 ment and for survival research on the schoohng 

 coastal pelagic fishes around the world, partic- 

 ularly sardine and anchovy. We want this manu- 

 script to be part of the celebration of Lasker's 

 career. We thank Roniulo Jordan S., Julio Val- 

 divia G., and Isabel Tsukayama, science direc- 

 tors of the Instituto del Mar del Peru during this 



'^Methot, R. D. 1986. Synthetic estimates of historical 

 abundance and mortality for northern anchovy, Eiigraiilin 

 mordax. U.S. Dep. Commer., NOAA, NMFS SWFC Adm. 

 Rep. U-86-29, 85 p. 



'Methot, R. D., and N. C. H. Lo. 1987. Spawning biomass 

 of the northern anchovv in 1987. U.S. Dep. Commer., 

 NOAA, NMFS SWFC Adm. Rej)., La Jolla, U-87-14, 37 p 



research, and their research staff. We also 

 acknowledge the support of Wolf Arntz in pro- 

 viding the travel and subsistence of the senior 

 author during this series of studies off Peru. We 

 also prize the assistance of four graduate stu- 

 dents from Peru: Veronica Blaskovich, Wilmer 

 Carbajal, Emperatriz Luyo, and Jorge Oliva. 

 We appreciate the assistance of Izadore Barrett, 

 John Butler, John Hunter, Alec MacCall, and 

 Daniel Pauly in reading this manuscipt. We 

 thank the Captain and crew of the IMARPE's 

 research trawler, Humboldt. 



LITERATURE CITED 



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