Red Tide, Fisheries Modeling and Citizen Science: Casting a Line to Anglers and Gulf of Mexico Stakeholders for Better Data!

Photo by scanning electron microscope of Karenia brevis aka red tide. Courtesy of FWC
Photo taken from a scanning electron microscope of Karenia brevis aka red tide. Photo By: FWC. * Banner photo: A red tide killed snook washed ashore in Southwest Florida. Photo By: Chris O’Meara AP.

In fisheries management, setting the acceptable biological catch (ABC) is vital to ensure sustainable harvest without overexploiting fish stocks. The ABC determines how much fish can be harvested each year, and is estimated using a stock assessment model that brings together multiple data sources to estimate fish abundance and productivity.  However, in the Gulf of Mexico, red tides introduce a lot of uncertainty into this process. Ongoing red tide blooms can leave managers guessing about their impacts on fish stocks when trying to set the ABC. This uncertainty about red tide impacts can lead to lower catch levels for commercial and recreational fishers, resulting in a lower ABC and less opportunities to bring fish home. To learn more about the ins and outs of  fisheries management in Florida, check out the third education module in the FREE Florida Friendly Angler online program!

Framework of harvest limits used in fisheries management

Red tides affect fish populations and ecosystems in several ways.  First, the brevetoxin released by red tide affects the central nervous system of fish and can result in large fish kills. Moreover, there are multiple sublethal and indirect effects of red tide such as low oxygen, impacts to benthic habitat, movement, and food web dynamics. Red tide could possibly alter the amount of bait/forage available for our prized game fish to eat and negatively impact the habitat where they live. In other words, a gag grouper that is exposed to red tide or poor water quality will have less food to eat, slower growth, and be less likely to survive, reproduce, and maybe one day be caught.  Combined with the fact that red tide doesn’t occur in the same place every time, with the same severity or duration makes estimating red tide impacts on reef fish species tough!

A sheepshead washed ashore from a red tide bloom in Southwest Florida. Photo By: Bryan Fluech.

To tackle this difficult task of estimating red tide impacts on fish stocks and helping make better informed management decisions, comes a new project that aims to a estimate and incorporating red tide mortality into the ABC determination for Gulf of Mexico (GoM) reef fishes. The “Operationalizing the West Florida Shelf ecosystem model and application to red tides, stock assessment, and catch advice for Gulf of Mexico reef fish project was funded by the NOAA Restore Science Program.  The project team is developing satellite products to map red tides that will inform an ecosystem model designed to account for factors like the severity and duration of red tide blooms, their lethal and sublethal impact on fish and other marine fauna, and ecosystem dynamics.

Bloom frequency maps from integration of water sample data and MODIS satellite observations. Figure adapted from Hu et al. (2022).

In previous work, the ecosystem model was used to inform the ABC for gag grouper, resulting in a longer fishing season because the impacts on ongoing blooms were estimated to be lower than anticipated.  The project team will refine the model’s inputs and extend its application to additional GoM reef fishes over the next five years. Furthermore, it will develop improved satellite-derived red tide maps and update biogeochemical models to estimate nutrient and oxygen dynamics. These model improvements will enable more precise estimation of red tide mortality rates on various reef fish species undergoing stock assessments. The project outcomes will be presented at workshops and incorporated into stock assessments, ensuring that the ABC reflects current red tide conditions. By operationalizing this modeling framework, fisheries managers can conduct routine red tide assessments, enhancing the sustainability of Gulf fisheries!

Where you can help!

Are you an angler, boater or beach goer living on the West Coast of Florida and wish to help researchers know more about red tide?

Then please consider taking this brief survey anytime you head out on the water and experience red tide.

The survey may be accessed via the hyperlink above or by copy and pasting this link into your browser: 

Information researchers are interested in includes: where did you encounter red tide? Did you see any dead/dying marine life? If so which species? Did your plans change due to encountering red tide? These and a few more questions can improve the models and help managers a TON by helping us determine how fisheries are affected by red tides!

An example of a question asked on the red tide survey to better understand where fish are dying, what species and how your trip may have been affected. Click the links above to access the survey to help fisheries science!

Have a question about red tide and fisheries management you would like answered? Submit your question via this link here and check back to this blog periodically where selected questions and answers will be posted!

A typical sight during a red tide bloom with both forage and game fish washed ashore. Help us determine which fish dying, where and when by responding to the reporting survey above! Photo By: Kate Spinner Sarasota Herald-Tribune.



Karenia brevis aka “red tide” cells swimming! These microscopic organisms belong to the dinoflagellate phylum of algae which have appendages that allow them to move around in the water column. The word dinoflagellate is derived from the Greek dînos meaning  “whirling” and Latin flagellum meaning “whip.” K. brevis’s unique motion helps researchers identify red tide cells from other phytoplankton and algae in a water sample.


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Posted: June 19, 2024

Category: 4-H & Youth, Coasts & Marine, Community Volunteers, Conservation, Disaster Preparation, Florida-Friendly Landscaping, Lawn, Natural Resources, Pests & Disease, Pests & Disease, Recreation, UF/IFAS, UF/IFAS Extension, UF/IFAS Research, , Water, Wildlife, Work & Life
Tags: Algae, Amberjack, Angling, Beach, Brevetoxin, Brevis, Charlotte County, Citizen Science, Collier County, Dinoflagellate, Ecosystem, FFA, Fish, Fish Kill, Fisheries, Fishing, Florida, Florida Friendly, Florida Friendly Angler, Florida Sea Grant, GoM, Grouper, Grunt, Gulf Of Mexico, HAB, Harmful Algae Bloom, Hernando County, Hillsborough County, Hogfish, Inshore, K. Brevis, Karenia, Lee County, Marine Biology, Modeling, Offshore, Pasco County, Phytoplankton, Pinellas County, Plankton, Red Tide, Redfish, Redtide, Reef Fish, Research, Seafood, Snapper, Snook, Tarpon

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