348 



Fishery Bulletin 103(2) 



B Kimberley 



Month 



Resting (F 2 and 3) 



Developing (F4) 



Spawning (F5 a b) 



Water temp 



Figure 3 



Annual cycle of Scombero?norus commerson reproduction within each 

 region, as indicated by macroscopically staged ovaries. Mid-month sea 

 surface temperatures are overlaid (solid line) and sample sizes are 

 shown above each column. 



12.7 kg WW. Both relationships were explained with 

 power curves: 



Batch fecundity 

 Batch fecundity 



 0.0011 x FL 2 896 ( r 2=0.441, n = 2l) 

 31087 x WW 1 ™ 4 (r 2 =0.714, n = 19). 



Annual reproductive cycle 



Female S. commerson within the Pilbara region were non- 

 reproductive between March and June, during the down- 

 ward cycle of water temperatures (Figs. 3 and 4). As water 

 temperatures reached a minimum in July and August 

 (around 24°C), a small proportion of mature ovaries had 



become reproductively developed (stage 4). The proportion 

 of developed ovaries during September (the start of the 

 upward cycle of water temperatures) varied noticeably 

 between years in the Pilbara region, from 18.5% to 79% 

 in 2001 and 2000, respectively. A small number of females 

 were also actively spawning when sampled during Sep- 

 tember 2000. Peak reproductive activity extended from 

 October to January, and spawning females were captured 

 during this period in 1999 and 2000 when the sea surface 

 temperature (SST) was rising from about 25.5° to 28.5°C. 

 By February, when SST peaked at approximately 30°C, 

 reproductive development was declining and the ovaries 

 of most females were spent or resting. 



