志々伎湾でみられたマダイとクロダイ仔稚魚の異なった分布様式〔英文〕

概要

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In Shijiki Bay of Hirado Island, diel discrete-depth horizontal tows with a larva net in May 1983 resulted in a total of 2, 350 larval and juvenile red sea bream (2.1-10.7mm SL), and 347 larval black sea bream (2.4-6.2mm SL) being collected. During the daytime, black sea bream larvae were concentrated near the surface, but red sea bream larvae near the bottom, with these tendencies becoming more evident with their growth. During the nighttime, the larvae of both species were dispersed throughout the water column. In the surf zone of the sandy-beaches located in the innermost part of the bay, collections with a small seine net in June and July 1983 gave a total of 241 late-larval and early-juvenile black sea bream (6.2-20.1mm SL), but no red sea bream. The separation of juvenile habitats between these related species seemed to be a consequence of the species-specific vertical distribution pattern differentiated during the pelagic larval period. A possible mechanism for inshore migration in the black sea bream was discussed in relation to their surface occurrence.