Returns of Chum Salmon Released from Net‐Pens and Rivers in Eastern Hokkaido, Japan

Abstract

AbstractThe effectiveness of net‐pen release of Chum Salmon Oncorhynchus keta in improving commercial coastal and river catches was examined by releasing marked fish from seawater net‐pens in Nemuro Bay or into the Nishibetsu River, eastern Hokkaido, northern Japan. Between 100,000 and 130,000 Chum Salmon fry were reared in the hatchery and marked by clipping either the left or right pelvic fin in 2006 and 2007; the fin clip was used to distinguish between net‐pen and river releases. Returning marked fish were surveyed in 17 set nets along the coast of Nemuro Bay, a small set net at the Betsukai Fishing Port, and a salmon weir in the Nishibetsu River 2–5 years after release. No differences were observed in the coastal catch period between the net‐pen‐released and river‐released fishes. Estimated coastal return rates of the net‐pen‐released fish (0.929% and 0.845%) were twice those of the river‐released fish (0.488% and 0.406%). However, six to seven times more river‐released fish (river catch rate = 9.591% and 7.513%) migrated upstream than net‐pen‐released fish (1.292% and 1.192%). Our results suggest that the use of marine net‐pens for Chum Salmon will not sustainably improve adult salmon catches in rivers, although it might increase coastal catches.