700 



Fishery Bulletin 100(4) 



A Inshore n = 1 039 



c Boffshoren=509 





^ <§^ <^ (§*<§' 'e '^ c? c^ <? ^^^ 



Fork length class (5 cm) 



Figure 6 



Percentage of macroscopic ovarian stages by 

 5-cm fork-length interval for Thyrsites atun 

 sampled (A) inshore and (B) offshore (i.e. 

 shorewards or seawards of the 1.50-m isobath) 

 during the spawning season (June-October), 

 1994-97. 



noteworthy component that declined in importance with 

 growth. In descending order, the most important prey 

 items were as follows: lanternfish Lampanyctodes hectoris 

 (IRI=46..5), euphausids Euphausia leucens (IRI=23), and 

 the amphipod Themisto gaudichaudi (IRI=14.2) for early 

 juveniles (5-24 cm); lanternfish (IRI=34.4), T. gaudichaudi 

 (IRI=32.4), anchovies (IRI=2.8), and sardines (IRI=2.4) for 

 juveniles (25-49 cm); anchovy (IRI=38.3), euphausids 

 (IRI=26), and sardine (IRI=11. 7) for subadults (50-74 cm); 

 and sardine (IRI=47.4) and anchovy (IRI=38.6) for adults 

 (>75 cm). 



In offshore waters snoek diet consisted almost exclu- 

 sively of teleosts. including pelagic and demersal taxa. The 

 most important prey items were sardine, round herring, 

 and hake (Merluccius spp.) for snoek <75 cm; and hake, 

 sardine and horse-mackerel (Trachurus trachurus cap- 

 ensis) for larger specimens. The main difference between 

 the two offshore diets consisted in the greater importance 

 of sardine (IRI=44.4 vs. 17.2 for snoek >75 cm) and the 



10 30 50 70 90 110 



Fork-length class (5 cm) 



Figure 7 



Percentage of mature (gonad stage 3-^) 

 Thyrsites atun by 5-cm fork-length class 

 sampled during the spawning season 

 (June-October), 1994-97. Symbols repre- 

 sent the observed data and the lines the 

 fitted models. L^fi= length-at-maturity (cm 

 fork length); n = sample size. 



lesser importance of hake (IRI=31.8 vs. 60.8 for snoek >75 

 cm) off the western Agulhas Bank than off the west coast 

 (Table 4). In both areas, large prey species, such as hake 

 and horse mackerel, were more important in the larger 

 (>75 cm) size class. 



Prey consumption 



Both indices of prey consumption — proportions of stom- 

 achs containing food and mean mass of stomach con- 

 tents — indicated that within each area and sampling 

 season, adult females consumed more prey than adult 

 males (Table 5); spatial and season trends were also evi- 

 dent. Two-way ANOVA with single observations revealed 

 that differences in the mean mass of stomach contents 



between sexes (F= 65.9, df=l, F,,., 



= 10.1) and between 



areas (F=215.5, df=3, F,.r,(,(a/=9-3* were both highly sig- 

 nificant (P<0.001). Chi-square tests revealed that dif- 

 ferences between the proportions of males and females 

 with stomach contents were highly significant inshore 

 on the west coast (WC) and offshore along the western 

 Agulhas Bank (WAB) in winter-spring, but were not 

 significant inshore on the WC in summer-autumn, or 

 offshore on the WC in winter-spring (Table 5). Female 

 mean stomach content mass was lowest (22.1 g) inshore 

 on the WC in summer-autumn and highest (60.1 g) off- 

 shore on the WAB in winter-spring (spawning season). 

 Female proportion with stomach contents was also lowest 

 (52.5%) inshore on the WC in summer-autumn but high- 

 est (81.2%) in the same area during winter Differences in 

 female proportions with stomach contents between sea- 

 sons inshore on the WC (j^^-gg 9 df=l), between inshore 

 and offshore areas of the WC in winter-spring (^^=130, 

 df=l) and between the offshore WAB and inshore WC 

 during winter-spring (^-=26.3, df=l) were highly sig- 



