"Responses of Coastal Largemouth Bass to Seasonal and Episodic Hypoxia in the Chowan River, NC"

In North Carolina, coastal Largemouth Bass Micropterus salmoides are highly sought after sportfish.  Bass populations inhabit river systems that experience seasonal and episodic periods of hypoxia that may influence their movement, habitat preference and mortality rates, yet few field studies have examined hypoxia avoidance of largemouth bass in open systems.  To address this issue, we implanted 48 largemouth bass with sonic telemetry tags during the spring of 2012 in the Chowan River, a coastal river system composed of a main channel and many tributaries, streams and extensive backwater habitat.  We monitored the movement of tagged bass using active tracking and passive receivers, and movement data were correlated with oxygen levels recorded via YSI datasondes.  No extended periods of hypoxia were observed during the first year of the study and mortality rates remained low.  Comparisons of movement patterns to fluctuations in dissolved oxygen revealed that tagged bass sought refuge in the mainstem during brief periods of hypoxia in the tributaries.  We observed seasonal trends in habitat preference as tagged bass moved further from shore and into slightly deeper water.  Results of this research should benefit fishery managers by identifying refuge habitats and quantifying seasonal and annual mortality rates.