Conservation and restoration of fourspine sculpin( Cottus kazika) in the Kuzuryu River

Abstract

The present study summarized the conservation and restoration of fourspine sculpin {Cottus kazika) in the Kuzuryu River from the past four research records. Many adults of C. kazika were found at depths of about 3 m (sea water) in the estuary of the Kuzuryu River and coastal shallow area neighboring the river mouth from the late of December to March (main season: from the middle of January to the middle of March). Larvae and juveniles were collected in sandy beach near the river mouth and shallow area in the estuary from February to April. Young of the year of C. kazika moved upstream with growing along the shallow water sides from April to August. The present remaining habitat of C. kazika was the middle area (23.0 to 29.4 km from the river mouth) in the Kuzuryu River. This indicated that the area of "Habitat of Araregako (C. kazika) in the Kuzuryu River (designated as a natural monument)" reduced to be one -third from 1990s onward, compared to that of the past habitat. The important habitats of the C. kazika, for both growing up and passing the winter, was riffles with loose bed materials in the river. Larger C. kazika more than 250 mm in total length weren't almost caught since 1990s by the traditional fisheries, which suggested that the body size of C. kazika has been shrinked in the Kuzuryu River. This study showed that two important conservation strategies for C. kazika in the Kuzuryu River are; 1) to conserve and create sandy beach in the coastal area neighboring the mouth of river, and riffles with loose bed materials in the present remaining habitat of Kuzuryu river, 2) to re-introduce juveniles of C. kazika with genetic diversity into upstream from Naruka-Oozeki (the past habitat) of the river.