Figure. DORSAL view of the viscera of S. oualaniensis. The large ovary contains developing eggs of many sizes. The oviducts are filled with mature eggs that have an orange tint. The black pigment is ink that has dribbled into the mantle cavity. Photograph by M. Vecchione.
An egg mass, spawned in captivity, by the giant form of S. oualaniensis from the Arabian Sea has a "typical ommastrephid" appearance (Chesalin and Giragosov, 1993) which would be a large spherical, gelatinous egg mass with thousands of eggs distributed thoughout the mass. Mature oocytes (eggs) are small, 0.70 mm x 0.84 mm (Sakurai, et al., 1995).
Paralarvae mostly occupy the upper 50 m of the ocean during both the day and night and often the upper 20 m although some can be found as deep as 80-100 m (Young and Hirota, 1998; Saito and Kubodera, 1993).
In Hawaiian waters paralarvae are present throughout the year but are most abundant in August, less abundant in April and least abundant in October and December (Harman and Young (1985). Some seasonal overlap occurs between the occurrance of paralarvae of S. oualaniensis and the related Ommastrephes bartramii in Hawaiian waters and the Northwestern Pacific; however, most of the spawning of these two species is out of phase in time and space over much of the year (Young and Hirota, 1990; Bower, et al., 1999; Saito and Kubodera, 1993).
Growth of paralarvae based on statolith increments indicates a paralarva of 4 mm ML is 30 days old which is in strong contrast to the growth of O. bartramii which reaches 7 mm ML at 30 days (Bigelow, 1991). Separation of the tentacles, usually thought to mark the end of the paralarval period in ommastrephids, occurred at about 9 mm ML in S. oualaniensis (Harman and Young, 1985). The validity of this event as the marker, however, has been questioned by Yatsu and Mori (2000).
Figure. Ventral and dorsal views of paralarval stages and the first juvenile stage of S. oualaniensis. Chromatophore patterns incomplete. Drawings from Harman and Young (1985).
Figure. Paralarval S. oualaniensis. Left - Oral view of the suckers at the tip of the proboscis. Photograph from Harman and Young (1985). Middle - Typical chromatophore pattern at 3.0 mm ML. Drawing from Young and Hirota (1990). Right - Photophore arrangement (blue): ocular photophores and two intestinal photophores. Drawing from Harman and Young (1985).
Juveniles are frequently found aggregated in inshore waters around oceanic islands (Okutani and Tung, 1978). The vertical distribution of juveniles is poorly known. Presumably they occupy near-surface waters during the day and night: Small S. oualaniensis have been found to glide onboard ship during the day (Young and Hirota, 1998), seen gliding over the surface of the ocean during the day (Arata, 1954; Young, 1975; Okutani and Tung, 1978) and found in the stomachs of day feeding birds (Ashmole and Ashmole, 1967). They are also encountered at the surface at night (Young and Hirota, 1998).
The diagnostic photophore patch on the anterodorsal surface of the mantle becomes apparent at approximately 100 mm ML (Kishimoto and Kohno, 1992; Nesis, 1993) and can be taken as a marker for the end of the juvenile phase and the beginning of the subadult phase of the life cycle. The hectocotylus develops about 110 mm ML (Okutani and Tung, 1978). Males of S. oualaniensis reach 15-17 mm in 6-7 months and are thought to live less than a year; the growth rates, determined by growth marks on statoliths and gladii, of the middle and dwarf forms are nearly the same, but the life span is short in the small forms, probably not more than 6 months Nesis (1993).
Yatsu (2000) determined growth curves for both male and female S. oualaniensis based on statolith increments from about 120 mm ML to about 290 mm ML for females and about 185 mm ML for males. His curves are: ML=9.9511X0.634 (females) and ML=29.9X0.3494 (males) with ML in mm and x=increments=days (presumably). According to this curve a female of 120 mm ML is 51 days old. This contrasts strongly with data of Zaidi bin Zakaria (2000), which places a 115 mm ML female at an age of 95 days. Since ommastrephid growth is affected by food availability and ambient temperature, growth rates can vary with season, geographic area and year (Yatsu, 2000).
In Hawaiian waters S. oualaniensis females mature between 158 and 205 mm ML with 50% mature at 166-175 mm ML and 90% mature at 200 mm ML (maximum size is 335 mm ML); males are mostly mature by 140 mm ML (maximum size is 210 mm ML) (Young and Hirota, 1998; Suzuki et al., 1986). In northern Australian waters males reached maturity from 160 mm ML and females from 250 mm ML.
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