Abundance of salmon carcasses at the upper reach of an adult salmon trap: Ten years of observation at a tributary of the Chitose River, Hokkaido, northern Japan
2009
Ito, T., Hokkaido Aquatic Biology, Eniwa (Japan) | Nakajima, M.
The abundance and biomass of salmon carcasses (Oncorhynchus keta and O. masou masou) were studied in a spring-fed tributary, the Naibetsu River, Chitose River system, Hokkaido, northern Japan, during 1998-2008. Almost all adult salmon are caught by an adult salmon trap each fall at the lower reach of the Chitose River for a salmon enhancement program. The abundance and biomass fluctuated annually and seasonally, with two peaks in the fall and winter. The range in carcass biomass was 0.05-10 kg/100 square m in fall and 0.4-61 kg/100 square m in winter. In some years, the biomass was greater than the lowest effective biomass for stream production, 5 kg/100 square m, which was evaluated in previous studies. The total number of carcasses in the fall was significantly correlated with the highest water level at the lower reach of the river, indicating that adult salmon swam over the trap at flood stage. Carcass abundance in winter may depend on the population size spawned in the wild at the upper reach.
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