豆南海域におけるサンマCololabis saira (BREVOORT) 稚仔の分布-II

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During 1955 and 1956 the authors conducted 87 survey cruises for distribution of larval forms of the saury pink, Cololabis saira (Brevoort) in Zunan Region extending from Sagami Bay to Torishima (Fig. 1). On the basis of the materials and data made available from the surveys, analyses have been made, in succession to a previous work, in regard to the distribution of the larvae and the length composition of the catch, which may vary depending on locality and year and be related with changes in oceanographical conditions in the region. The number of individuals of the larvae collected at each station is listed in Tables 1 and 2 together with the data pertinent to total length, gear used and so forth. Noticeable features those tables reveal are as follows. 1) Stations in the vicinity of Torishima showed the distribution in a greater density than any other offshore station. 2) In the inner niche of Sagami Bay, where a water boundary exists, about 150 individuals accrued from a single haul of a larval net. 3) Generally speaking, 856 larvae collected with a dip net between Aogashima and Torishima were greater in total length than those obtained at most of larval netting stations. By sorting the samples into several groups according to the locality, time and gear of collection, the total length frequency has been compared among the different groups (Fig. 2). As is evident in Fig. 2, the catches both by dip net and by larval net indicate that the length class where the mode takes place is greater in 1956 than in 1955. Considerable numbers of the larvae measuring about 10 centimeters or less in total length occurred in Sagami Bay and in the neighbourhood of Torishima. Furthermore, 18 adults which occurred off Torishima in early March of 1956 and measured 28.83±1.46cm in body length apparently belonged to a spawning group. These facts suggest that the saury pink spawn substantial quantity of the young in these general localities. According to oceanographical surveys carried out by the R. V. Tonan Maru along a longitudinal line connecting the Izu Islands during the period from 1954 to 1956, the locality of the water boundary between the Kuroshio Current and the littoral waters is moving further offshore one year after another (Fig. 3). Apparently the movement of the water boundary has been dependent on the status of a cold water mass off Enshu Nada. On the other hand, the larval distribution has been nearly twice greater in the Kuroshio Countercurrent area than in the Kuroshio Current area flowing eastwards (Tables 3 and 4). On the basis of these findings it is inferable that a close relation exists between translocation of the major basin of the Kuroshio Current and changes in the spawning conditions of the saury pike and particularly in the length composition of the young whose mode has been found greater one year after another. Frequency of surface temperature at the collecting stations, showed that nearly 75 percent of the stations had the temperature ranging from 18° to 21°C (Table 5).
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豆南海域におけるサンマCololabis saira (BREVOORT) 稚仔の分布-II

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