Influence of Coastal Seawater Temperature on the Distribution and Growth of Juvenile Chum Salmon, with Recommendations for Altered Release Strategies

摘要

In 2002 we initiated a project to determine the optimal timing for releasing juvenile hatchery chum salmon in rivers along the northeast coast of Hokkaido in northern Japan. Otolith-marked juveniles released in mid May 2002 and 2004 were captured by a surface trawl net 1 km off the coast in late May. In contrast, juveniles released in mid May 2003 were not observed in coastal waters until early June, along with chum released in late April of the same year; fish from these releases were captured in littoral areas in mid/late May with beach seines. In addition, early growth rates for juveniles released in late April 2003 and subsequently captured 1 km off the coast were lower than for juveniles released in mid-May. Juvenile chum rapidly disappeared from coastal waters after late June when sea surface temperatures (SST) were > 13°C. While relatively high juvenile abundances were found in coastal waters from May to June in 2002 and 2004, when SST ranged from 8 to 13°C, this water temperature range occurred in coastal waters only in June 2003. In contrast, SSTs from 7 to 12°C were found in the littoral zone in May 2003. Offshore marine movement of juvenile chum appears to depend on seawater temperature rather than fish size, especially considering that water temperatures < 8°C appeared to restrict movement offshore. We caution against releasing juvenile chum salmon when coastal water temperatures are < 7°C or> 11°C.