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Neuse River & Pamlico Sound
The most common species captured include; Atlantic croaker (Micropogonias undulatus), spot (Leiostomus xanthurus), bay anchovy (Anchoa mitchilli), blue crab (Callinectes sapidus), Atlantic menhaden (Brevortia tyrannus), shrimp (2 species), silver perch (Bairdiella chrysoura), weakfish (Cynoscion regalis), harvestfish (Peprilus alepidotus), southern flounder (Paralichthys lethostigma), pinfish (Lagodon rhomboides), bluefish (Pomatomus saltatrix), summer flounder (Paralichthys dentatus).
Fish typically used the entire estuary until hypoxic zones restricted them to oxygenated areas.
We found that fish were rarely captured in waters with low dissolved oxygen concentrations, our catch per unit effort dramatically decreased in waters with dissolved oxygen concentrations of less than 1.5-2.0 mg/l.
In 1999, we tagged southern flounder (Paralichthys lethostigma) with ultrasonic transmitters, released them into experimental depth and dissolved oxygen treatments in the river, and then tracked them to investigate how fish movement and habitat use may be influenced by the formation of hypoxic zones. We found that a flounder left hypoxic areas moving into shallow, well oxygenated areas within two hours. Tracking data over the longer term revealed that flounder had small home ranges and fish generally remained near shore experiencing hypoxia only when it encroached into the shallow waters. Fish experiencing hypoxia moved more than fish that did not experience low oxygen. Therefore, episodic hypoxia influences fish behavior by altering habitat use and movement rates.
We ran in situ caging experiments in 1999 with juvenile croaker (Micropogonias undulatus) to examine how hypoxia may influence growth rates for juvenile fish. We found that hypoxia can impact juvenile fish growth rates by displacing fish to less profitable habitat, killing prey resources in areas exposed to hypoxia, and potentially crowding fish in the oxygenated refuges at high enough densities to see density dependent decreases in growth rates. Projections from experimental results would predict that if juvenile croaker were to be displaced by hypoxia intermittently throughout the summer, growth rates could decrease about 30% over the summer at the site that experienced intermittent hypoxia.
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