卜ド:保護から管理への転換

摘要

Steller sea lions Eumetopias jubatus (SSL) originated from Okhotsk rookeries experienced an acute population decline by half from the 1960s to the 1980s partly due to hunting in Japan, on which virtually no regulation had been enforced. A provisional annual quota of 116 animals was mandated in the early 1990s, and then the SSL began to rebound at the rate of 4% a year. However, fishing damages due to SSLs has been serious accounting for >1 billion JPY yr~(-1) for the last 20 yrs. Hunting has been one of the mitigating measures of the damages, and has been regulated by means of PBR during 2008-2013. After the degrading of SSL in the Red Lists (IUCN and Japan Ministry of Environment) in 2012,the management has been requested to be revised. The revision intended to control the number of SSLs migrating to the western coast of the Hokkaido Island, and a virtual population comprising the migrators has been assumed. In the purpose of fishing damage mitigation, the target level of the migrators in 2024 was set to be 60% of the present level (i.e. 40% depletion). We constructed a simple population model to describe the dynamics of the population based on the catch history and aerial surveys, and an annual harvest level including bycatch was calculated. This is one of the first implementations of the "from conservation to management” volte-face in the pinniped around the Pacific Rim, and should be followed by a careful monitoring of the SSL and precautious and adaptive management revisions, to avoid its fall below the endangered level again.