The future without restoration could potentially lead to increasing sea level rise and salinities within the basin that could be detrimental to current oyster lease production. However, the future with restoration projects, like sediment diversions, also have significant and complex concerns and implications.
I have been fortunate to be part of an interdisciplinary group of academic men and women assembled to investigate different Mid-Barataria diversion flow scenarios and discuss how to balance land building with the need to maintain an estuary with salinity for coastal fisheries, wildlife and vegetation. This is our second assemblage as a group. Results of our first assemblage centered on discussions and development of a conceptual model on how a diversion might operate more during the cold winter months with limited openings after, and limited spring operations on the rising limbs of the Mississippi River’s flow stages(4).
Sediment diversions and oysters may be able to co-exist. I am on record some years back stating that oysters and diversions can co-exist. But at that time a large diversion was considered 30,000 cubic feet per second (cfs), and today a large diversion is 2.5x bigger at 75,000 cfs(2). That is why I change from “can” to “may”. Much will depend on operation plan and what months when to divert.
There are many crucial questions yet to answer. For example, “Will the diversion run only during cold water months? ; once the diversion is closed, how long for estuary recovery time to ambient salinities? ; and, will the spring spawn be delayed or lost, and if lost can the fall spawn produce and survive enough to sustain the fishery?” Some questions are being addressed now, while others will take monitoring and slowly testing the diversion to see how the estuary as a whole with multiple species, and oysters in particularly respond.
The Barataria Estuary today is one of the most commercially and recreationally important habitats within the northern Gulf of Mexico for many species, not just oysters(3). Our ongoing efforts are not to give definitive answers on how to operate a river diversion, as that may change annually and over time, but to add information to help the state in conjunction with User Groups within the Barataria Estuary to come to an agreed operation and adaptive management plan that takes all views into account, and to monitor and analyzes the effect of diversion operations on oysters and other fisheries. It is crucial to make operational adjustments to meet multiple objectives of building and sustaining the coast while also sustaining harvestable populations of commercial and recreational species.
(1) Earl J. Melancon et al. (1998). Oyster Resource Zones of the Barataria and Terrebonne Estuaries of Louisiana. Journal of Shellfish Research 17(4):1143-1148
(2) Supplemental Notice of Intent To Prepare a Draft Environmental Impact Statement (DEIS) for the Proposed Mid-Barataria Sediment Diversion, in Plaquemines Parish, Louisiana. Federal Register /Vol. 82, No. 80/Thursday, April 27, 2017/Notices
(3) Thomas J. Minello et al. (2017). Fisheries Habitat in Estuaries of the U.S. Gulf of Mexico: A comparative assessment of Gulf Estuarine Systems. NOAA Technical Memorandum NMFS-SEFSC-702.
(4) Natalie S. Peyronnin et al. (2017). Optimizing Sediment Diversion Operations: Working Group Recommendations for Integrating Complex Ecological and Social Landscape Interactions. Journal Water 9(368); doi:10.3390/w9060368.
(5) Louisiana Dept. Wildlife and Fisheries presentation to the Louisiana Oyster Task Force, July 30, 2019.