NCCOS-supported scientists have determined that this year’s Gulf of Mexico “dead zone” — an area of low oxygen that can kill fish and marine life — is approximately 3,058 square miles, equivalent to more than two million acres of habitat potentially unavailable to fish and bottom species.

This measurement brings the five-year average to 4,347 square miles, which is more than two times larger than the 2035 target set by the Mississippi River/Gulf of Mexico Hypoxia Task Force (HTF). The annual dead zone survey was led by scientists at Louisiana State University and the Louisiana Universities Marine Consortium (LUMCON) during a research cruise from July 23 - July 28 aboard the LUMCON R/V Pelican.

In June 2023, NOAA forecasted a below-average sized hypoxic zone of 4,155 square miles (the record of 8,776 square miles was set in 2017). While the model results overestimated the measured size of the zone this year, they were within the expected margin of uncertainty for the forecast and provide further evidence of the robustness of the models to relate nutrient inputs to observed hypoxia size in the summer.

The HTF uses the annual hypoxic zone size determination as a key metric to measure progress toward achieving the five-year average target of 1,900 square miles or smaller by 2035. Maintaining ongoing summer surveys and calculating a five-year average allows scientists to capture the true dynamic nature of the zone more than a single annual measurement. 

Exposure to hypoxic waters has been found to alter fish diets, growth rates, reproduction, habitat use and availability of commercially harvested species like shrimp.  For the past two years, scientists from North Carolina State University and NOAA Fisheries have been using an experimental model to better forecast shrimp distribution relative to the hypoxic zone. NOAA has also been continuing to work in collaboration with States to develop new tools to forecast runoff risk, which help limit nutrient runoff to waterways by identifying the optimal times for fertilizer application within these and other watersheds.

In addition to its annual hypoxia forecast and survey, NOAA supports efforts to develop monitoring technologies to understand and map the dead zone, as well as to study the impacts of hypoxia on fish and fisheries in the Gulf of Mexico and elsewhere through its Coastal Hypoxia Research, Ocean Technology Transition, Uncrewed Systems, and Hypoxia Watch Programs. Furthermore, NOAA continues to partner with and support the Northern Gulf Institute to deliver technical assistance, observation and monitoring and coordination across federal, state, academic, and private sector scientists.  

For more information about the 2023 Gulf of Mexico dead zone, view the NOAA Press Release or watch this Ocean Today video.