Seasonal changes in depth and temperature of habitat for Japanese flounder Paralichthys olivaceus on the Pacific coast of northeastern Japan

Seasonal changes in habitat use in terms of depth and temperature were estimated for Japanese flounder Paralichthys olivaceus from the Pacific coast of northeastern Japan from 2006 to 2008, using data from trawl and gillnet fisheries logbooks, to which we assigned monthly estimates of bottom temperature. Estimated distributions of flounder for depth and temperature were validated by actual depth and temperature readings from data storage tags (DSTs) attached to flounder, and from collection records by trawl survey. Year-round, flounder > 300 mm in total length were present mainly in areas < 100 m in depth, although their depth range extended to similar to 100 m in summer and similar to 200 m in winter. Flounder experienced cold temperatures (< 10 degrees C) for several months during winter and spring, and cooler temperatures (< 18 degrees C monthly mean) in summer, with a range from 4.6 degrees C to 21.0 degrees C. This temperature range of the habitat is lower than recorded for this species elsewhere in Japan, and seemed to affect regional life-history traits such as growth and spawning season. DST readings indicated that flounder experienced higher temperatures during vertical swimming behavior than bottom temperatures when the water was stratified (May-October), which may also influence life-history traits.