FISUKKY BULLETIN: VOL H6. NO 1 



Figure 8. — Relationship between clasper size and body size 

 in Mobula japan ica . 



^150 



O o 

 Z.<2 

 liJ^125 



UJ " 

 CO "O 



^« 



O §100 



# s«mlnal fluid preteni 

 O seminal fluid absent 

 A no data 





.\. 



1500 2000 



DISC WIDTH (mm) 



2500 



thurstoni, since most of the specimens of M. 

 japanica were of larger size classes. It was appar- 

 ent, however, that at a DW between 2,050 and 

 2,150 mm there is a high degree of variability in 

 the relative size of claspers, which tended to sta- 

 bilize at higher values (DWs >2,150 mm), indi- 

 cating that male sexual maturity in M. Japanica 

 begins at a DW of 2,100 (±50) mm. Lack of infor- 

 mation on smaller specimens prevented a clear 

 understanding of the onset of female sexual ma- 

 turity (Fig. 9). Large eggs were found in speci- 

 mens as small as 2,070 mm DW, possibly indicat- 

 ing that female M. japanica began to mature at 

 that size. 



Only 19 (24%) of 78 specimens had quantifiable 

 stomach contents (>1 g wet WT). The remaining 

 59 stomachs (76%) were empty or had only traces 

 of food. All M. japanica fed largely on the eu- 

 phausiid Nyctiphanes simplex (Table 4); no 

 mysids were found. Other species occurring in the 

 stomachs, including copepods, megalopa larvae, 

 stomatopod larvae, hyperiid amphipods, caridean 

 decapods (Crangon sp., Pasiphaea sp., and one 

 alpheid decapod), and one cumacean, had an over- 

 all relative diet importance of only 0.38%>. Mobula 

 japanica were therefore very similar in feeding 

 habits to large M. thurstoni. Information on the 



Figure 9. — Relationship between size of largest ovum and 

 body size in Mobula japanica . 



2000 2200 



DISC WIDTH (mm) 



2400 



Table 4. — Prey species found in 19 stomachs of Mobula japanica, ranked by decreas- 

 ing Index of Relative Importance (symbols as in Table 2). 



58 



