Estuarine fish behavior around slotted water control structures in a managed salt marsh

Estuaries are composed of multiple interconnected habitat types used by transient fish species during their period of estuarine residency. Structural marsh management restricts habitat connectivity and impedes the movement of fishes among these habitat types by limiting access via water control structures (WCSs) between the managed area and the rest of the estuary. While some general information on fish passage rates is available, species-specific information on passage through WCSs is lacking for salt marsh fishes. We monitored tagged fishes from March 2012 through November 2013 using passive integrated transponder antenna arrays at two identical WCSs in the Calcasieu Lake estuary, Louisiana, USA, to assess the effect of slotted WCSs on fish behavior. A total of 420 individuals of 15 species was tagged and released at the WCSs; of these, 145 individuals representing 11 species were later detected at the WCSs. Five species comprised most (93%) of the detected individuals: Elops saurus (n = 60), Mugil cephalus (n = 43), Sciaenops ocellatus (n = 20), Pogonias cromis (n = 7), and Ariopsis felis (n = 5). Passage rates were low, with most of the observed fishes (n = 80) passing only once through the structures. Other than E. saurus, which was only observed migrating out of the managed marsh, no clear pattern in swimming direction was observed for the other species. Detected species were all present primarily during the summer and fall, however, diel activity at the structures varied by species. The WCSs in our study area appeared to attract and congregate fishes, functioning more like ecological hotspots, rather than simply facilitating fish passage.