Studies on Environments Alluring Skipjack and Other Tunas-II:On the Driftwoods Accompanied by Skipjack and Tunas

概要

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The object of this paper is to clarify the characteristics of the drifting woods on the ocean that are accompanied by skipjack and tunas from close observation of the woods themselves. In 1952-1963 the authors had opportunities to obtain the data on the drifting woods through cooperation of many commercial fishing vessels and research vessel Tokaidaigaku Maru. The specimens of the dritfwoods are shown in Table 1 and Fig. 1. The woods followed by skipjack and tunas showed a peculiar biological environment as shipworms and other shells attached on the outside or into the inside of the woods. Dominant animals found on the driftwoods that were accompanied by skipjack and tunas were Teredora aurita and Lepas anserifera. Dominant sessils animals to driftwoods that were not accompanied by skipjack and tunas were Lepas anserifera, which were found in plenty, Planes minutus, and barnacles, Balanus sp. The difference between woods accompanied by skipjack and tunas and those not accompanied by these fish seems to lie in the existence or non-existence of Teredora aurita. Judging from the length of the burrows caused by Teredora aurita, the authors presume that driftwoods turn to attract skipjack and tunas behind them while the driftwoods were drifting on the sea for at least one year.