Decrease of Abalone Resources with Disappearance of Macroalgal Beds Around the Ojika Islands, Nagasaki, Southwestern Japan

ABSTRACT Because abalone feed mainly on macroalgae, the disappearance of macroalgal beds would have negative effects on abalone. We investigated the relationship between abalone resources and quantitative or qualitative changes of algal beds in coastal waters around the Ojika Islands, Nagasaki Prefecture, southwestern Japan, from 1988 to 2011. During this period, the catch record of 2 abalone species—Haliotis discus discus and Haliotis gigantea—was examined, and the composition and abundance of macroalgae around the Ojika Islands was observed. The annual landing of abalone has decreased steadily from 91 mt in 1987 to 0.4 mt in 2011. The proportion of H. discus discus to the annual abalone landing has also changed; it was stable (30%–60%) between 1988 and 2000, less than 20% from 2004 to 2005, and increased from 2006, reaching more than 90% in 2010. The macroalgal beds have also changed during this period. The perennial Laminariales beds, consisting of Eisenia bicyclis and Ecklonia spp., had disappeared by...