Simulating Fish Movement Responses to and Potential Salinity Stress from Large‐Scale River Diversions

Abstract

River diversions are a major but controversial management approach to restoring coastal wetlands and mitigating offshore oil spills in the northern Gulf of Mexico. One of the controversies concerns the potential displacement of and salinity stress on commercially and recreationally important fish species in response to the widespread and prolonged freshening of habitat. We developed a coupled hydrodynamics–fish movement model and applied it to the Caernarvon diversion located in the Breton Sound estuary, Louisiana. Hydrodynamics model output was used as input to the individual‐based fish movement model. The period of model simulation was from April 1 to July 1, 2010. We simulated three diversion scenarios: baseline, pulse, and oil spill mitigation. We first used field data from Bay Anchovy Anchoa mitchilli and showed that the model predicted downestuary shifts similar to those observed in field studies under large diversions. We then defined generic low‐ and intermediate‐salinity fish species and simulated each under the three diversion scenarios. Compared with the baseline diversion scenario, more than 50% of the intermediate‐salinity individuals moved about 15 km farther downestuary under the pulse diversion scenario and moved more than 35 km under the oil spill mitigation diversion scenario. The effects of the diversions on the low‐salinity species were evidenced by individuals becoming more dispersed (i.e., spreading out downestuary) and more exposed to bursts of too high salinity. Our conclusions agreed with those from earlier field and modeling analyses that focused on average (rather than transitory) fish responses. Received November 4, 2013; accepted November 7, 2013

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