At night squids are commonly observed in surface waters. suggest, based on the near In Hawaiian waters subadults and adults of S. oualaniensis are usually absent from surface waters at night over bottom depths of less than 650 m,which suggests that they descend to at least 650 m during the day (Young and Hirota, 1998). Simarily, Dunning (1998) caught adult S. oualaniensis in eastern Australian waters only where bottom depths exceeded 600 m.
In many geographical areas of S. oualaniensis distribution, deep water can have low oxygen concentrations which should exclude its presence. Indeed, S. oualaniensis has a very high metabolic rate (standard metabolism of 348 ml O2 kg-1 h-1) that exceeds that of most fast-swimming oceanic fishes (Zuev, et al., 2002). Its energy metabolism, as in other squids, is based mostly on protein; however during metabolism a considerable proportion of the protein is catabolized anaerobically (Shullman et al., 2002). In this sense, these squid may be "preadapted" for low oxygen environments. In the Indian Ocean large S. oualaniensis occupy depths of 300-400 m during the day where the oxygen concentration is 0.1-0.2 mg/liter (2-4% of saturation) (Shullman et al., 2002).
S. oualaniensis is a tropical IndoPacific species that occurs in the Pacific from southern Japan to southern Queensland and from just south of Baja California to northern Chile (Nesis, 1987). Dunning (1998) records S. oualaniensis as far south as 38°40'S (SST 20.7°C) at the northern edge of the Bass Straits, near the coast of Australia. In the Coral Sea Basin (east of 155°E), however, adults were caught only north of 32°S (SSTs>23.5°C). Eastward from the Coral Sea to near the coast of South America Wormuth (1976) records its presence roughly along 20°S to about 110°W then his southern records reach about 15°S but stop about 4° of longitude west of Peru apparently at the edge of the Peru current. In the region of the Hawaiian Archipelago, S. oualaniensis did not occur in winter north of 28°N. Between 23°N and 28°N large females were few and of those few most were not mature; the ratio of mature to immature females of squid 200 mm ML or larger was 1:27 during one cruise (Young and Hirota, 1998). This suggests that at the northern end of their range, the females are not maturing normally. Tung et al. (1973) states that Taiwan (which lies roughly between 22 and 25°N) is at "the edge area of the migration sphere of the common squid [S. oualaniensis] in the southwest water of Taiwan... ." S. oualaniensis is recorded off Southern Japan at nearly 35°N (SST 25-26°C) (Saito and Kubodera (1993). Wormuth (1976) recorded the northern limit of distribution at 33.6°N and 165.5°E (September) and about 31°N at 156°W, 139°W and 129°W off Southern California west of the California Current. During the change of seasons the SSTs across most of the Pacific undergo a dramatic north-south movement. For example, north of Hawaii the 18°C isotherm can move from near 3O°N in February to over 40°N in August (Laurs and Lynn, 1991). The extent to which the latitudinal limits of the distribution of S. oualaniensis change with season are not known but do not appear to be very dramatic.
S. oualaniensis exhibits small-scale areal patterns in the vicinity of islands. Around the Hawaiian Islands large mature females are located on the windward (northeastern) sides of the islands, small immature females are located primarily within 25 km of the leeward (southwestern) sides of the islands and somewhat larger mostly immature females are found mainly further offshore on the leeward sides of the islands (Young and Hirota, 1998). The reason for these patterns is unknown but Young and Hirota (1998) found some differences in feeding patterns between windward and leeward areas. These local patterns and those observed in juveniles (Okutani and Tung, 1978) and in paralarvae (Bower, et al., 1999) indicate modified distribution patterns in the vicinity of islands.
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