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Investigation into Unusual Fish Behavior in the Florida Keys

Published on: 05/15/2024
Region(s) of Study: U.S. States and Territories / Florida
Primary Contact(s): sarah.pease@noaa.gov
overhead image of four people in a dive boat: two divers at the back of the boat prepare to enter the water while two people at the front of the boat prepare samples

Florida Gulf Coast University students, Nick Frankenburger and Kenzie Pruitt getting ready to dive while staff, Adam Catasus and Rachael Schinbeckler, prepare samples. (Credit: Andrew Tipler)

The Florida Fish and Wildlife Conservation Commission (FWC) has received nearly 500 reports of unusual fish behavior from the Lower Florida Keys since last November, with over 52 species of fish affected, including endangered smalltooth sawfish. Affected fishes swim in circles at the water’s surface and lose their ability to stay upright when exposed to bright light at night. While the cause of the fish behavior remains unknown, initial water samples collected where fish exhibited these behaviors indicated high concentrations of benthic harmful algae. Unlike Florida red tide, which is caused by a type of harmful algae that is usually found at the water’s surface, benthic harmful algae are associated with, or occur on, the bottom of a body of water, where benthic species like sawfish live and feed.  

NOAA’s National Centers for Coastal and Ocean Science (NCCOS) Harmful Algal Bloom (HAB) Event Response Program awarded $25,000 to Florida Gulf Coast University, Bonefish & Tarpon Trust (BTT), and the University of South Alabama to investigate the high concentrations of benthic harmful algae and potential links to the unusual fish behavior being observed in the Lower Florida Keys. Staff from BTT, the Lower Keys Guides Association, and Everglades National Park are acting as researchers’ “eyes on the water,” using methods developed during previous studies to collect samples to help detect benthic harmful algae. One aim of the research is to determine the spatial extent of the elevated concentrations of benthic harmful algae in the region. The team is collecting samples of seagrasses and benthic macroalgae to identify and quantify any associated harmful algae or harmful algae toxins. They will also test tissue samples collected from fish exhibiting abnormal behavior for harmful algae toxins.  

The research team’s work is part of a wide, collaborative response to this ongoing event affecting fish in the Florida Keys. Scientists from NCCOS’ Phytoplankton Monitoring Network also identified elevated concentrations of benthic harmful algae in water and seaweed samples from the Florida Keys, corroborating the HAB research team’s initial findings. These samples were collected and sent by Florida Atlantic University researchers. Additionally, NOAA Fisheries and FWC are coordinating an emergency response effort specific to the endangered sawfish impacted by this event. Personnel from the HAB and sawfish response efforts are collaborating to share information and ideas as they continue to investigate the cause of the unusual fish behavior in the region. 

The NCCOS HAB Event Response Program provides immediate support to help state, tribal, and local officials manage events and advance the understanding of HABs as they occur. For more information about the NCCOS HAB Event Response Program, contact us at nccos.hab.event.response@noaa.gov.

To report a related fish kill, diseased fish, fish with other abnormalities, or discolored water, contact the Florida Fish and Wildlife Conservation Commission’s (FWC) Fish Kill Hotline: (800) 636-0511. If you see a sawfish in distress, call the Sawfish Hotline at 844-4-SAWFISH (844-472-9347) or email sawfish@myfwc.com

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