Occurrence of a temperate coastal flatfish, the marbled flounder Pseudopleuronectes yokohamae, at high water temperatures in a shallow bay in summer detected by acoustic telemetry

Abstract

The marbled flounder Pseudopleuronectes yokohamae, a flatfish found in temperate coastal waters, is an important commercial species in the northwestern Pacific Ocean, but little is known of its distribution and movement under high water temperatures in summer. We recorded the distribution and movement of marbled flounder in shallow water in Tokyo Bay with acoustic telemetry. Seventeen wild flounder tagged with acoustic transmitters were tracked/monitored by active tracking using a research vessel and sporadic monitoring using fishing gear and a fishing boat. We located six individuals in shallow (< 30 m) water at temperatures of 19–23 °C and dissolved oxygen (DO) concentrations of 3–5 ml/l in Tokyo Bay, while bottom water temperatures and DO concentrations ranged from 19 to 24 °C and 0–7 ml/l, respectively. Our results indicated that at least 35% of the flounder remained in warm, shallow waters in summer. Multiple monitoring methods and the assistance of fishermen helped to overcome the difficulties of working in a crowded bay and increased our recovery rate of the tagged flounder.