Juvenile weakfish Cynoscion regalis distribution in relation to diel-cycling dissolved oxygen in an estuarine tributary

Abstract

Publisher's PDF.Shallow estuarine waters that serve as nurseries for fishes along the Atlantic and Gulf coasts of the USA can undergo wide diel dissolved oxygen (DO) fluctuations (2.0 mg O2 l–1, weakfish were more abundant at the upper site than at the middle and lower sites, which also experienced severe hypoxia but at much lower frequency. However, under all environmental conditions they were absent from the upper site whenever bottom DO was <2 mg O2 l–1, and returned within 2 h of DO exceeding 2 mg O2 l–1. Daily up- and down-creek movement occurred over a distance of ~1 km. These findings indicate an avoidance threshold of ~2.0 mg O2 l–1 for juvenile weakfish and demonstrate very temporally dynamic DO-related movement. Their rapid return to these areas as DO conditions improve, and relatively high density in tidal tributary headwaters, suggests that these relatively small areas provide important habitat for fishes.University of Delaware. School of Marine Science and Policy