Predicting the effects of low salinity associated with the Mid-Barataria Sediment Diversion project on resident common bottlenose dolphins (Tursiops truncatus) in Barataria Bay, Louisiana

In this analysis, we develop a simulation approach to evaluate the probable effects of changes in salinity in Barataria Bay, Louisiana associated with the Mid-Barataria Sediment Diversion (MBSD) project on the resident common bottlenose dolphin stock. This population occurs throughout the Bay with a total estimated population size of 2,071 (95% CI: 1,832 – 2,309) animals. Dolphins occur in the highest densities near the barrier islands and the associated passes. Under various alternative diversion scenarios, the MBSD project is expected to reconnect the flows of freshwater, sediment, and nutrients from the Mississippi River into the northern portion of the Bay on an annual basis. This action is intended to rebuild marsh areas and reduce land loss. The preferred alternative (Applicant’s Preferred Alternative) sets a maximum instantaneous inflow from the project at 75,000 cubic feet per second. Two additional alternatives of differing discharge capacities are being considered in addition to the “No Action Alternative,” where the current and future conditions are considered without the project. Daily salinity surfaces from the Delft3D hydrodynamic model were used to assess the changes in the distribution of low salinity (< 5 parts per thousand) in the Bay and subsequent projected impacts on the bottlenose dolphin population. We used information on the initial spatial distribution of dolphins, simulated dolphin movements, modelled exposure to low salinity, and an expert elicitation-based dose-response curve relating exposure to low salinity to survival to estimate expected annual survival rates for the bottlenose dolphin population.

Garrison, L.P, Litz, J. and Sinclair, C. 2020. Predicting the effects of low salinity associated with the MBSD project on resident common bottlenose dolphins (Tursiops truncatus) in Barataria Bay, LA. NOAA Technical Memorandum NOAA NMFS-SEFSC 748: 97 p.