Title Current status and problems of isoyake in Japan
Authers Daisuke FUJITA
Citation Bull. Fish. Res. Agen. No.32, 33-42, 2010
In Japan, decrease of seaweed beds has been noticed by fishermen for more than a century and called isoyake. In the modern context, isoyake is defined as decrease or disappearance of upright seaweed beds resulting in the formation and maintenance of poorly vegetated area on the shallow bedrock and stony beds, other than seasonal and slight yearly fluctuations. Seaweeds decrease when they were grazed / browsed by herbivores (e.g., sea urchins and/or herbivorous fish), withered in waters with high water temperature, inhibited for germlings to attach and grow by sedimentation, and/or detached in storms. Some are natural, but the others are highly anthropogenic. The resultant poorly vegetated areas occur most often offshore of seaweed beds, sometimes zoned between shallow and deep beds or patched among the beds. Isoyake has increased during the 20th century; now most of coastal prefectures have more or less isoyake areas. The restoration of seaweed beds has often been unsuccessful because (1)drastic changes in coastal environments, (2) misunderstanding of isoyake, (3) inappropriate selection of restoration method, (4) decrease of young fishermen, (5) limited information on planning and measures, (6) short of social support system, (7) limited commercial usages for priceless herbivores. In 2007, Fisheries Agency published an official guideline for promoting restoration of seaweeds. The principle shown in the guideline is the removal of factor(s) inhibiting formation of seaweed beds; the recommended actions include the adaptive management and collaboration among fishermen, administrative, specialists and citizen. The guideline has been popularized by local meetings and demonstrated in restoration trials lead by supporters, i.e., experienced specialists. Now urchin barrens are highly recoverable to seaweed beds by removing sea urchins, but further technical developments are needed to restore seaweed beds when barren maintains by other factors, e.g., herbivorous fish, high density of snails or sedimentation.
URI http://www.fra.affrc.go.jp/bulletin/bull/bull32/33-42.pdf