クロアワビ放流稚貝の死亡について

概要

論文の詳細を見る
The cultured seedings of Japanese black abalone Haliotis discus discus were transplanted to a rocky coastal area at Asakawa in Tokushima Prefecture, southern Japan, during May 1975 and 1976. About 100 individuals ranging from 8mm to 18mm in shell length were released at four releasing positions each year. The abalone were released in a cage made of netting (5mm in mesh size) at station 1b, in order to prevent animals from intruding. These abalone were observed under water by skin diving for 7 days in 1975 and 8 days in 1976. The rate of survival in both large and small tide pools was very low ranging from 0.0% to 4.0% but was 51.6% at station 1b. In the channel, the released abalone were observed under spines of sea urchin Anthocidaris crasspina and the rate of survival was 23% and 28%. About half of the empty shells were broken around the margin, 7.1-55.4% of the empty shells were broken in pieces. Further experiments on predation were conducted in laboratory tanks, using animals which were collected at the releasing positions. The small crab Gaetice depressus could prey upon young abalone smaller than 15mm in shell length. The shells of abalone killed by this crab were either damaged or not damaged. The crab Charybdis japonica ate those smaller than 27mm in shell length. All of the shells of abalone killed by this crab were broken in pieces.