Shelton and Hutchings, Ocean stability and anchovy spawning in southern Benguela Current region 



337 



comparative study of eastern-boundary currents by 

 Parrish et al. (1983) that the spawning habits of an- 

 chovy (and sardine) attempt to minimize both wind- 

 induced turbulent mixing and offshore-directed trans- 

 port. Bakun (1985) argues that the results of Parrish 

 et al. (1983) strengthen the relevance of Lasker's 

 hypothesis to modeling recruitment and exploratory 

 data analysis. However, if anchovy populations in the 

 different eastern-boundary current regions have essen- 

 tially "solved" the problems of disruptive turbulence 

 and unfavorable transport, "mistakes" should be rare 

 and difficult to find in the field. The fact that event- 

 scale disruptive turbulence has been observed in the 

 spawning area off southern California and that the in- 

 cidence of calm periods can be statistically related to 

 daily larval mortality rate (Lasker 1975, 1981b; Peter- 

 man and Bradford 1987) suggests that such "mistakes" 

 do occur despite adaptations. Even so, they may be 

 undetectable in recruitment measurements, either 

 because of large and often unquantified measurement 

 error, or because the "mistakes" are masked by a well- 

 developed suite of "bet-hedging" traits (Shelton 1987). 

 Estimates of anchovy recruitment (with error bars) for 

 the southern Benguela population based on direct 

 surveys (Butterworth 1989, Fig. 16) show less variabil- 

 ity than anticipated in the literature (e.g., Beddington 

 and Cooke 1983), although the time series is still too 

 short to be conclusive. 



If the southern Benguela anchovy population is 

 adapted to local persistent patterns of ocean stability 

 and is well-buffered against event-scale variations 

 through bet-hedging, a prerequisite for detectably poor 

 recruitment at moderate spawning stock sizes may be 

 season-long weakening or disruption of the stability 

 patterns in either the spawning, transport, or recruit- 

 ment areas. Such conditions would probably arise if the 

 influence of Agulhas Current water over the Agulhas 

 Bank and on the west coast were reduced, particular- 

 ly over the summer period. 



Acknowledgments 



We acknowledge the input of several of our colleagues 

 at the Sea Fisheries Research Institute, Cape Town, 

 to the Cape Egg and Larval Programme. In particular. 

 Garth Newman and Vere Shannon provided much of 

 the impetus for the initiation of CELP, and Alan 

 Robertson, Hennie Crous, Frans Kriel, Deon Horst- 

 man, Donald Alexander, Robert Cooper, Gustav Weh- 

 meyer, Jan Van der Westhuizen, Chris Jeenes, John 

 Giddey, and Christine Illert gave excellent technical 

 support during its execution. Colleagues at the NMFS 

 Southwest Fisheries Center, La Jolla, particularly the 

 group formally headed by Reuben Lasker, are thanked 



600- 



z 



LU 



S 400- 



200- 





81 



82 



83 



84 85 

 YEAR 



86 87 



88 



Figure 16 



Estimates (median and 95% confidence interval) of annual anchovy 

 recruitment for the southern Benguela population, deduced from 

 direct survey results to July 1988 (Butterworth 1989). 



for their advice and encouragement with respect to the 

 studies of anchovy early-life history in the Benguela 

 Current system. We dedicate this paper to the memory 

 of Reuben. 



Citations 



Andrews, W.R.H., and L. Hutchings 



1980 Upwelling in the southern Benguela Current. Prog. 

 Oceanogr. 9:1-81. 

 Armstrong, D.A., B.A. Mitchell-Innes, F. Verheye-Dua, 

 H. Waldron, and L. Hutchings 



1987 Physical and biological features across an upwelling front 

 in the southern Benguela. In Payne. A.I.L, J. A. Gulland, and 

 K.H. Brink (eds.), The Benguela and comparable ecosystems. 

 S. Afr. J. Mar. Sci. .5:171-190. 



Armstrong, M., P. Shelton, I. Hampton, G. Jolly, and Y. Melo 



1988 Egg production estimates of anchovy biomass in the 

 southern Benguela system. Calif. Coop. Oceanic Fish. Invest. 

 Rep. 29:137-157. 



Arthur. D.K. 



1976 Food and feeding of larvae of three fishes occurring in 

 the California Current, Sardinops sagax, Engraulis mordax 

 and Tmchurus fiijinmetricus. Fish. Bull., U.S. 74:517-530. 

 Bakun, A. 



1985 Comparitive studies and the recruitment problem: 

 Searching for generalizations. Calif. Coop. Oceanic Fish. 

 Invest. Rep. 24:30-40. 

 Bang, N.D. 



1973 Characteristics of an intense ocean frontal system in the 

 upwelling regime west of Cape Town. Tellus 25:256-265. 



Bang, N.D., and W.R.H. Andrews 



1974 Direct current measurements of a shelf-edge frontal jet 

 in the southern Benguela system. J. Mar. Res. 32:405-417. 



