METHOT: SURVIVAL OF LARVAL ENGRAUUS MORDAX 



Northern anchovy larvae which are transported 

 offshore may experience higher larval mortality 

 rates, and the survivors may be unable to return to 

 the inshore juvenile nursery areas. Monthly indices 

 of upwelling (Bakun 1973) at lat. 30° and 33°N, rela- 

 tive to long-term monthly means, were exceptionally 

 low during January-March 1978 (downwelling 

 occurred) and remained below normal through May 

 1978 (McLain and Ingraham 1980). Seckel et al. 

 (1978) suggested that these conditions entrained lar- 

 vae close to shore and correctly predicted an abun- 

 dant 1978 year class. However, the results obtained 

 here suggest that larval survival was higher during 

 late spring 1978 than during the winter when 

 downwelling occurred. 



Upwelling was as low in December 1978 and 

 January 1979 as in winter 1978, but the storms were 

 less severe in 1979. Later in 1979, upwelling was near 

 normal. The increased upwelling in 1979 relative to 



1978 may have been responsible for the greater 

 offshore displacement of northern anchovy larvae in 



1979 (Table 4). The transport hypothesis correctly 

 predicts a poorer year class in 1979 relative to 1978 

 and decreasing larval survival through the 1979 

 spawning season. 



This brief examination of environmental data does 

 not completely account for the patterns of recruit- 

 ment of the northern anchovy in 1978 and 1979. 

 Indices of offshore transport seem more important 

 than indices of food availability, but the seasonal pat- 

 tern of survival in 1978 could not be explained by 

 transport. It is simplistic to assume that only one fac- 

 tor is involved in recruitment and that the effect of 

 this factor is linear. One plausible scenario is that the 

 winter storms of 1978 caused high mortality of early 

 larvae, but the low upwelling throughout the year per- 

 mitted high entrainment of late larvae and resulted in 

 the good year class. It is also possible that the 

 extremely low upwelling during winter 1978 did not 

 have a proportionally greater effect than the low 

 upwelling of spring 1978. Relatively low upwelling 

 late in the spawning season may be important 

 because absolute upwelling and transport typically 

 increase through the spring (Smith and Lasker 1978). 

 The spawning season may be timed to avoid low food 

 availability in winter and high transport in late 

 spring. 



Other evidence indicates that survival of early 

 northern anchovy larvae was nearly constant during 

 the 1978 and 1979 spawning seasons. Hewitt and 

 Methot (1982) inferred larval mortality from the 

 slopes of the larval age- frequency distributions and 

 found no significant seasonal changes. This evidence 

 is consistent with the hypothesis that the significant 



change in survival which caused the difference in re- 

 cruitment occurred after the early larval stage. 

 Adverse larval drift would not necessarily cause 

 increased mortality during the age interval examined 

 by Hewitt and Methot but may affect the fraction of 

 the surviving larvae which are entrained in the range 

 of the juvenile habitat. 



LITERATURE CITED 



Bakun, A. 



1973. Coastal upwelling indices, west coast of North 



America, 1946-71. U.S. Dep. Commer., NOAA Tech. 



Rep. NMFS SSRF-671, 103 p. 

 Beyer, J. E., and G. C. Laurence. 



1981. Aspects of stochasticity in modelling growth and sur- 

 vival of clupeoid fish larvae. Rapp. P.-V. Reun. Cons. Int. 

 Explor. Mer 178:17-23. 



Brothers, E. B., C. P. Mathews, and R. Lasker. 



1976. Daily growth increments in otoliths from larval and 

 adult fishes. Fish. Bull., U.S. 74:1-8. 



Collins, R. A., and J. D. Spratt. 



1969. Age determination of northern anchovies, Engraulis 

 mordax, from otoliths. In J. D. Messersmith (editor), The 

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CONOVER, W. J. 



1971. Practical nonparametric statistics. Wiley, N.Y., 

 462 p. 



CUSHING, D. H. 



1975. Marine ecology and fisheries. Camb. Univ. Press, 

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 CUSHING, D. R, AND J. C. K. HARRIS. 



1973. Stock and recruitment and the problem of density 

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 FRIDRICKSSON, A. 



1934. On the calculation of age-distribution within a stock of 

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 Hewitt, R., and R. D. Methot, Jr. 



1982. Distribution and mortality of northern anchovy larvae 

 in 1978 and 1979. CalCOFI Rep. 23:226-245. 



H.JORT, J. 



1926. Fluctuations in the year classes of important food 

 fishes. J. Cons. Int. Explor. Mer 1:5-38. 

 Hunter, J. R. 



1972. Swimming and feeding behavior of larval anchovy 

 Engraulis mordax. Fish. Bull., U.S. 70:821-838. 



KlMURA, D. K. 



1977. Statistical assessment of the age-length key. J. Fish. 

 Res. Board Can. 34:317-324. 



Kramer, D., M. J. Kalin, E. G. Stevens, J. R. Thrailkill, and J. 

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1972. Collecting and processing data on fish eggs and larvae 

 in the California Current region. U.S. Dep. Commer., 

 NOAA Tech. Rep. NMFS Circ. 370, 38 p. 

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1975. Field criteria for survival of anchovy larvae: the relation 

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