404 



Fishery Bulletin 94[3). 1996 



i.ii 

 40 



20 

 



60 

 40 

 20 







604. 



40 



20 

 



60 

 40 

 20 





 60- 

 40- 

 20- 



Hokusei Main IWI 



/; = 368 



....lllllllv^ 



Townsend Cromwell IW2 

 n = 550 



HokuseiMaru iw.l 



/i = 44S 



o-^ — i — r "" 1 — — i — — r 



15 January I February 1 5 February I Mareh ISMareh I April 



Estimated hatch date 



Figure 4 



Frequency of projected hatch dates for Om mast replies bartramu 

 paralarvae captured during five surveys. Horizontal bars represent 

 sampling dates. 



to obtain good estimates of ages and hatch dates of 

 O. bartramii paralarvae. 



Growth in mantle length of O. bartramii para- 

 larvae was characterized as exponential for at least 

 23 days after hatching. This observation agrees with 

 that of Bigelow and Landgraf ( 1993 ), who found that 

 growth in length of this species is exponential for at 

 least 35 days posthatching. The growth rates of other 

 posthatching ommastrephids have also been shown 

 to be exponential (Illex sp., Balch et al., 1988; Illex 

 argentinus, Arkhipkin, 1989; Stenoteuthis oua- 

 laniensis, Bigelow, 1991). Because growth in 

 ommastrephids during later life tends to be linear 

 or nearly linear, these data suggest that the overall 

 form of growth may be approximately described as 

 sigmoidal. 



Estimated hatch dates of individuals collected dur- 

 ing the three years surveyed ranged between mid- 

 January and early April. Young and Hirota (1990) 



estimated that paralarvae caught in 1986 were 

 spawned between late February and early April. As 

 noted by Young and Hirota (1990), spawning may 

 occur over a longer period, but synoptic surveys were 

 conducted only between February and April. Surface 

 plankton tows, conducted while the vessel drifted, 

 and nighttime jigging at a sampling station 100 ki- 

 lometers north of Oahu during March 1992, June 

 1992, December 1992, and April 1993, caught nei- 

 ther adult nor paralarval O. bartramii (Bower, per- 

 sonal observ. ). More extensive nighttime jigging off 

 the northeast coast of Oahu during mid-September- 

 early October 1992 failed to capture adult O. 

 bartramii (Bower, personal observ). Harman and 

 Young ( 1985) failed to catch O. bartramii paralarvae 

 off leeward Oahu during December 1983, April 1984, 

 August 1984, and October 1984. 



Paralarvae captured over the five surveys showed 

 a fairly broad size range of about 1-8 mm mantle 



