FISHERY BULLETIN: VOL. 87, NO. 1 



for a positive selective value for migrating to the 

 west coast to spawn. At the same time, increased 

 rates of growth by older larvae away from the 

 spawning area suggest equally strong selection to 

 ensure that, as they develop, larvae are transported 

 away from the west coast. Larvae achieve the max- 

 imum growth rate only by being at the right place 

 at the right stage of their development. Hence, 

 migration of M. novaezelandiae to a specific spawn- 

 ing area and subsequent contra-natant migration of 

 larvae away from that spawning area appears to be 

 neither evolutionarily trivial nor solely the result of 

 selection to place eggs and larvae upstream of some 

 specific nursery habitat. Rather, it is an adaptive 

 feature of the reproductive biology of the fish that 

 relates directly to elements of its larval ecology. 

 Further, if survival of larvae varies with growth 

 rate, as has been widely suggested (Hunter 1981; 

 Rosenberg and Haugen 1982; Folkvord and Hunter 

 1986), then spatial effects on rates of larval growth 

 can provide a mechanism that links current vari- 

 ability with year-class strength in M. novaezelan- 

 diae. We have, as yet, no direct evidence for such 

 a link in this species but such a hypothesis has been 

 frequently proposed for marine fishes (Walford 

 1938; Sette 1943; Harden Jones 1968; Nelson et al. 

 1977; Parrish et al. 1981). In most cases, however, 

 emphasis has been placed on the adverse effects of 

 advection, in which inappropriate current patterns 

 result in larvae being transported into oceanic 

 habitats not well suited for their development. For 

 example, Devonald (1983) and Theilacker (1986) pre- 

 sented evidence that larval mackerel, Trachurus 

 symmetricus, found well off the California coast feed 

 less well and are in worse condition than those col- 

 lected closer to shore, which is consistent with the 

 adverse effects of offshore transport on year-class 

 strength suggested by Parrish et al. (1981). In con- 

 trast, advection is not a negative factor in M. 

 novaezelandiae: larvae do better when advected 

 away from the spawning area at the right stage of 

 their development. Such a positive effect of advec- 

 tion is impHcit in hypotheses involving spawning 

 grounds, nursery areas, and adult habitats that are 

 spatially separated (Harden Jones 1968; Shelton and 

 Hutchings 1982). Data for most species, however, 

 are still too sparse to determine the general signif- 

 icance of a direct, positive effect of advection on 

 rates of larval growth like that in M. novaezelandiae. 



ACKNOWLEDGMENTS 



We thank S. Blaber and G. Harris, and the other 

 members of the CSIRO Temperate Program for 



their assistance and advice throughout this study; 

 the captain and crew of the RV Soela for making 

 possible the field sampling; G. Leigh and S. Wayte 

 for assistance in statistical analyses; A. Gronell and 

 K. Sainsbury for invaluable discussions of the results 

 of the study as they developed; G. Cresswell, C. 

 Fandry, and C. Nilssen for advice on the physical 

 oceanography of Tasmanian coastal waters; F. 

 Boland and D. McLaughlan for assistance with 

 deploying the drogue; N. Elliott for help with the 

 drift cards; G. Davis and A. Paul for assistance in 

 the laboratory; R. Frie for providing a copy of his 

 program DISBCAL; and S. Blaber, F. R. Harden 

 Jones, G. Jenkins, V. Mawson, and P. Rothlisberg 

 for reviewing the manuscript and offering helpful 

 suggestions. This study was supported in part by 

 grant number 1984/63 from the Fishing Industry 

 Research Trust Account. 



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