232 



Fishery Bulletin 91(2). 1993 



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Figure 9 



Proportion of mature female Lutjanus vittus with (a) early 

 and (b) late-stage postovulatory follicles plotted against 

 time of sampling. Samples taken during periods of spawn- 

 ing (lunar days 2-10 and 18-29) during November-De- 

 cember 1982. Shown are 95% binomial confidence limits 

 for proportions and number in each sample. 



vittus tends to comply with Grimes' (1987) generaliza- 

 tion that continental species, regardless of latitude, 

 have a restricted spawning season. 



The pattern of restricted spawning in L. vittus may 

 be linked with the production cycle on the NW Shelf, 

 as has been suggested for other continental species of 

 lutjanids (Grimes 1987). The nutrient source is slope- 

 water washing up onto the NW Shelf in summer when 

 the Leeuwin Current is no longer flowing (Holloway et 

 al. 1985, Tranter & Leech 1987). Enrichment is great- 

 est between December and April. In winter the south- 

 east trade winds blow, there is little stratification of 

 the water column, and the plankton are dispersed 

 (Tranter & Leech 1987). These winds abate by late 

 August or early September, enabling the water col- 

 umn to become highly stratified and the plankton more 

 concentrated (Tranter & Leech 1987). This would re- 

 sult in improved feeding conditions for larvae and co- 

 incides with the start of major spawning activity. 



During the major spawning period, individual L. 

 vittus spawn a number of times. Serial spawning has 



been inferred in a number of lutjanids: L. purpureus 

 (De Moraes 1970), L. kasmira (Rangarajan 1971), L. 

 griseus (Campos & Bashirullah 1975), L. synagris 

 (Erhardt 1977), Prist ipomoides multidens and P. typus 

 (Min et al. 1977), Rhomboplites aurorubens (Grimes 

 Huntsman 1980), P. filamentosus (Ralston 1981), Etelis 

 carbunculus (Everson 1984), E. coruscans and Aprion 

 virescens (Everson et al. 1989). While serial spawning 

 appears to be commonplace in lutjanids, the number 

 of batches of eggs spawned each season has not been 

 determined conclusively for any species (Grimes 1987). 

 Our data suggest that L. vittus spawn about 22 times/ 

 mo during late November and early December. If this 

 spawning intensity were maintained throughout the 

 whole spawning period (October-April), then most in- 

 dividuals would spawn about 150 times/yr. Even if 

 spawning intensity were half this rate for the remain- 

 der of the season, thenL. vittus would spawn about 90 

 times/yr. 



Greatest spawning activity in L. vittus was shortly 

 after the full and new moons. A lunar rhythm in spawn- 



