Implications of Recreational Fishing on Juvenile Masu Salmon Stocked in a Hokkaido River

Freshwater recreational anglers in northern Japan sometimes catch significant numbers of juvenile masu salmon Oncorhynchus mason, thereby reducing the effectiveness of enhancement activities aimed at increasing marine catches of adult masu salmon. We stocked 66,500 juvenile masu salmon in the Shirai River, a major tributary of the Yoichi River in Hokkaido, northern Japan, during October 2005. Surveys conducted during the month after stocking revealed that approximately 65 fish/angler-day were caught, and catch varied between fishing gears (bait or fly) and locations (upper or lower reach). Estimated total number (mean +/- SE) of Fish harvested was 5,647 +/- 2,394, equivalent to 8.5 +/- 3.6% of the fish stocked. The estimated number of fish remaining in the river at the end of the angler survey was 57,246 +/- 8,595, and survival rate during this month was 86.1 +/- 12.9%. While releasing hatchery-reared masu salmon in late fall can reduce fishing mortality in rivers compared with earlier releases, mortality Could be further reduced by dispersing fish over large areas that contain locations with overwintering habitat.