350 



Fishery Bulletin 103(2) 



A Pllbara (HL-97. WW-304. HW-232) 





g 



■u 

 £ 1 



B Kimberley (HL-31 9. WW-443. HW-40) 



I 





I • 



Date 



HL index 



WW index 



HW index 



Figure 5 



Annual cycle of gonad indices for Scomberomorus commerson in Western 

 Australia for (A) Pilbara, (B) Kimberley, and (Cl West Coast regions. Sample 

 sizes are given for each index, where HL = head length index, WW=whole 

 weight index, and HW=head weight index. 



West Coast region were collected over a range of SSTs, 

 including when it was at a minimum (Figs. 3 and 4). 



Gonadosomatic indices calculated from whole weight, 

 head weight, and head length exhibited similar patterns 

 and confirmed the spawning cycle determined from ex- 

 amination of ovaries (Fig. 5). The most complete data 

 set was for females from the Pilbara region. In this re- 

 gion indices were minimal between March and August 

 and increased considerably during September as ovaries 

 became reproductively developed. Peak indices occurred 



in November 1999 and October 2000, coinciding with 

 peaks in the proportion of spawning (stage 5) ovaries 

 in the samples. The drop in gonad indices during De- 

 cember 1999 showed that the supplies of vitellogenic 

 oocytes within the ovaries were reduced by this time, 

 even though many females were still spawning (Fig. 4). 

 This drop continued until March when all the ovaries 

 in the samples were in the resting stage. Data for 2001 

 indicate that decreased GSIs during the reproductive 

 season were comparable to data from the previous two 



