Milton and Blaber: Sexual maturity and spawning of tuna baitfish in the Solomon Islands 



227 



Figure 6 



Monthly variation in proportion 

 (±95% confidence limits) of 

 female Spratelloides delicatulus 

 and S. lewisi spawning at three 

 sites in the Solomon Islands, 

 March 1987-May 1989. 



(a) Munda 

 S. delicatulus 



MAMJ J ASOND J FMAMJ JASONDJ FMAM 



(b) Vona Vona 



MAMJ JASONDJ FMAMJ JASONDJ FMAM 



(c) Tulagi 



X 



MAMJ JASONDJ FMAMJ JASONDJ FMAM 



1987 1988 1989 



Time (months) 



S. lewisi 



MAMJ JASONDJ FMAMJ JASONDJ FMAM 



C 

 C 



5 



a. 



0) 



o 

 a 



MAMJJASONDJFMAMJJASONDJFMAM 



tt«tT<i » i i tiii»ii*i»» ) i * r rr> 



MAMJ JASONDJ FMAMJ J ASONDJ FMAM 



1987 1988 1989 



Time (months) 



heterolobus also had fewer, smaller peaks in spawning 

 activity during most of 1987 at Tulagi and at all sites 

 during the first five months of 1989. Encrasicholina 

 devisi in Munda and Vona Vona did not have a March- 

 May spawning peak in 1989. 



Spratelloides Two Spratelloides species also showed 

 inter- and intraspecific differences in spawning activ- 

 ity between sites and between years (Fig. 6). Spratel- 

 loides delicatulus spawned continuously during 1987 

 at both Munda and Vona Vona, but the proportion 

 spawning declined in the next 17 months. At Tulagi, 

 the pattern was reversed, with less spawning during 

 1987 than in 1988-89 when there was a single major 

 protracted spawning season from December to March 



(Fig. 6c). Spratelloides lewisi showed seasonal spawn- 

 ing activity at all sites. Fish from Vona Vona and Tulagi 

 had a similar pattern during 1987-88, with increased 

 spawning activity from October to May. However, the 

 proportion spawning at Tulagi (50%) was much lower. 

 The spawning activity of S. lewisi at Munda showed 

 no seasonal increase during 1987, although during 1988 

 a higher proportion was spawning during the middle 

 of the year (Fig. 6). 



Too few S. gracilis and A. zosterophora could be ob- 

 tained to determine their spawning seasons. However, 

 a proportion of the fish sampled of both species was 

 in spawning condition for several months of the year 

 (Fig. 7). Archamia zosterophora data from Munda 

 showed that some spawning activity occurred through- 



