瀬戸内海におけるサヨリの産卵 : II.流れ藻に産みつけられた卵の漂流経路と運命

概要

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Drifting seaweeds were labeled with post-paid reply cards sealed in polyethylene envelopes and liberated during the spawning season of the halfbeaks, April-June, in 1964. One hundred and fourty two reply-cards from 912 labeled seaweeds were recovered. Halfbeak eggs on drifting seaweeds do not drift a great distance in their incubation period, though they move very intricately in some limited areas. The maximum drift distance of eggs is 27 miles so far as the result is concerned. It is estimated that some 70 per cent of drifting seaweeds and their lives as drifting seaweeds within 15 days (viz. incubation period of halfbeaks). Supposing that each halves of the natural decrease in drifting seaweeds is due to casting up ashore and sinking to the sea bottom respectively, some 35 per cent of the halfbeak eggs are considered to be killed before hatching. There are several places where concentrated cast up of drifting seaweeds is observed. It must be effective to make some facilities along these coasts to prevent drifting seaweeds and halfbeak eggs on them from being casted up.
1966-10-01