THE BACKWATER WAND-POOL AND THE OLD CHANNEL AS JUVENILE CHUM SALMON HABITAT AROUND THE TOKACHI RIVER MOUTH

Abstract

In an old channel and a wand-pool located in the estuary of the Tokachi River in East Hokkaido, chum salmon fry were collected six times, approximately every 2 weeks from 12 April to 7 June 2018, using seine and cast nets. The most abundant catches occurred in mid and late April in the old channel and the wand-pool, respectively. These periods differed from the period during which the highest number of salmon were released from a nearby hatchery. During mid and late April, the water temperature around the Tokachi River estuary was approximately 3°C, which is unsuitable for juvenile activity. Individuals collected from the wand-pool were found to be feeding on lentic benthic macroinvertebrates. Otolith analysis indicated that about half of the fry captured in April may have been wild fish. The old channel and the wand-pool in the estuary may have function to reduce the initial depletion of chum fry. In areas of salmon habitat, chum fry conservation should be incorporated into plans for wand-pool construction.