Abstract. -The reproductive bi- 

 ology of Lutjanus vittus, an impor- 

 tant component of the trawl-fishery 

 catch from the North West Shelf of 

 Australia, was determined from ran- 

 dom, stratified trawls made every 

 2 mo during August 1982-October 

 1983. The smallest mature female 

 was 142 mmFL; half of the females 

 at 154mm (estimated 1+yr of age) 

 were mature. The major spawning 

 season was from September to April, 

 although some spawning occurred in 

 other months. A semilunar pattern 

 of spawning activity was observed, 

 with peaks in the proportion of 

 spawning females -3 d after the new 

 moon and 6d after the full moon. 

 Individuals spawn about 22 times 

 each lunar month. The diel changes 

 in proportion of fish with ripe oo- 

 cytes and early- and late-stage 

 postovulatory follicles, together with 

 data on maximum oocyte diameter, 

 suggest that most individuals spawn 

 between 11:00 and 15:00h on peak 

 spawning days. The relationship 

 between batch fecundity (F) and 

 fish fork length (L in mm) was expo- 

 nential (F=3. 656x10-" L 4093 ) and 

 with fish weight (W, g) was linear 

 (F=124.2xW-3081). Unlike gonad 

 weight, batch fecundity did not 

 decline as the spawning season 

 progressed. 



Maturation, reproductive 

 seasonality, fecundity, and 

 spawning frequency in Lutjanus 

 vittus (Quoy and Gaimard) from 

 the North West Shelf of Australia 



Tim L.O. Davis 



Grant J. West 



CSIRO Division of Fisheries, Marine Laboratories. 

 GPO Box 1 538, Hobart, Tasmania 7001. Australia 



Manuscript accepted 17 February 1993. 

 Fishery Bulletin, U.S. 91:224-236 ( 1993). 



Lutjanids are of great importance in 

 fisheries throughout the tropics and 

 subtropics, and Lutjanus vittus dis- 

 tributed throughout the Indo-West 

 Pacific is a highly valued component 

 of the multispecies trawl fishery of 

 the North West Shelf of Australia 

 (NW Shelf), comprising -4% of the 

 total catch of ~ 165,000 1 between 

 1972 and 1980 (Jernakoff & Sains- 

 bury 1990). Its early life history 

 has been studied in Japan (Mori 

 1984); its biology, in New Caledonia 

 (Loubens 1980a,b). Information on 

 growth and mortality of this species 

 on the NW Shelf has recently been 

 published (Davis & West 1992). How- 

 ever, there is no published informa- 

 tion on the reproductive biology of 

 L. vittus that would pertain to the 

 management of this fishery on the 

 NW Shelf. 



Some information on the reproduc- 

 tive biology of over 40 species of 

 lutjanids is available (see review by 

 Grimes 1987). Many studies have in- 

 dicated that lutjanids are multiple 

 spawners, based on the evidence of 

 multimodal size-frequency distribu- 

 tions of oocytes, but techniques such 

 as the hydrated oocyte and post- 

 ovulatory follicle methods (Hunter & 

 Goldberg 1980, Hunter & Macewicz 

 1980), for measuring spawning fre- 

 quency in marine fishes, have not 

 been applied to lutjanids (Everson et 

 al. 1989). In this paper we present 



data on oocyte development, size-at- 

 maturity of females, and batch fecun- 

 dity in L. vittus from the NW Shelf. 

 We also demonstrate both diel and 

 semilunar spawning periodicity 

 through an analysis of the temporal 

 distribution of hydrated oocytes and 

 early- and late-stage postovulatory 

 follicles, and provide estimates of 

 spawning frequency and annual 

 fecundity. 



Materials and methods 



Specimens were obtained from the 

 CSIRO North West Shelf program 

 between August 1982 and October 

 1983 (Young & Sainsbury 1985). De- 

 tails of the two-monthly random 

 stratified trawl surveys of shelf wa- 

 ters within latitudes 116°E and 119°E 

 are given in Davis & West (1992). A 

 subsample of 20-40 Lutjanus vittus, 

 which approximately represented the 

 size-frequency composition of the to- 

 tal catch (Kimura 1977), was selected 

 from each random trawl. Fork length 

 was measured to the nearest 1 mm 

 and total weight to the nearest lg. 

 Fish were sexed and up to 200 ova- 

 ries per cruise were fixed in 10% for- 

 malin in seawater for histological and 

 whole oocyte examination. Additional 

 biological samples were collected 

 from nonrandom trawls to investigate 

 lunar and diel periodicity in spawn- 



224 



