Unusual Mortality Event: 2018-2019 Southwest Bottlenose Dolphins
In July of 2018, elevated bottlenose dolphin mortalities occurred and were associated with the red tide bloom along the southwest coast of Florida including Collier, Lee, Charlotte, Sarasota, Manatee, Hillsborough, and Pinellas counties.
Why are you closing the Unusual Mortality Event?
The conditions under which the UME was declared are no longer occurring. Scientists are no longer documenting a marked increase in strandings. The team of scientists who investigated this UME determined the cause of the UME as being due to biotoxin exposure (brevetoxin) from a Karenia brevis harmful algal bloom off the coast of southwest Florida.
How widespread was this Unusual Mortality Event?
Increased mortalities of bottlenose dolphins were observed along the southwest Florida coastline. Strandings occurred in Collier, Lee, Charlotte, Sarasota, Manatee, Hillsborough, and Pinellas counties.
What are the dates for this UME? How many bottlenose dolphins are included in this UME?
The UME was defined as occurring from July 1, 2018, through June 30, 2019, and during this time 183 bottlenose dolphins were documented.
What do scientists believe is the most likely cause of this UME?
After analyzing various differentials relative to available data, scientists say the cause of this UME was biotoxin exposure (brevetoxin) from a Karenia brevis harmful algal bloom off the coast of southwest Florida.
What unusual ocean conditions occurred in 2018-2019?
Beginning in November 2017 and continuing through February 2019, there was a persistent red tide (Karenia brevis, brevetoxin) nearshore and in the bays and estuaries of central west and southwest Florida red tide concentrations becoming more extensive and widespread in June 2018. Red tide cell counts began to subside in December 2018 and March 2019 was the first month where cell counts were not present or at background levels along the West coast of Florida. Furthermore, data suggests that there is a lag between the presence of a harmful algal bloom and increased cetacean mortalities, this lag is due to the biotoxin moving up trophic levels, first impacting prey-related species, and then dolphins. It is not uncommon to have red tide occur in Southwest Florida, however, in 2017-2019, the red tide bloom continued much longer, was larger, and was present in central and southwest Florida through February 2019. Additionally, there were concurrent fish, and other species die-offs linked to brevetoxin during the same time period along the Florida coast.
What did scientists test for? What did they find?
Although many carcasses were too decomposed to allow for necropsies, the samples scientists were able to gather were examined for biotoxin exposure. 95% (126/132) of the dolphins tested positive in at least one tissue at background (<50 ng/g) or higher brevetoxin concentrations, and 56% of dolphins (74/132) had high positive brevetoxin concentrations (> 200 ng/g) in at least one tissue.
What is a red tide? What are red tide toxins and how do they impact dolphins?
A red tide, or harmful algal bloom, is a higher-than-normal concentration of a microscopic alga (plantlike organism). In Florida and the Gulf of Mexico, the species that causes most red tides is Karenia brevis. Karenia brevis produces brevetoxins that can affect the central nervous system of fish and other vertebrates such as dolphins, manatees, birds, and sea turtles, causing these animals to become ill and die. Wave action can break open Karenia brevis cells and release toxins in the air, leading to respiratory irritation. Dolphins, manatees, and turtles can be exposed to the toxins by consuming prey fish or seagrass contaminated with the toxin or by breathing the toxin released from the algal cells. Additional information about red tide can be found at: https://oceanservice.noaa.gov/news/redtide-florida/.
What types of marine mammals did this UME affect?
This event involved bottlenose dolphins (Tursiops truncatus), which is one of the most common marine mammal species found in the coastal waters of the Gulf of Mexico.
What is next now that the Unusual Mortality Event has been closed?
Scientists plan to continue post-UME monitoring the bottlenose dolphins in southwest Florida for the next several years. Expected steps include:
- Continue monitoring of stranding demographics and pathologic findings in stranded dolphins across southwest Florida especially monitoring for future algal bloom and biotoxin impacts.
Where can I find additional information on bottlenose dolphins and other Unusual Mortality Events?
What should people do if they encounter a dead dolphin floating or stranded on the beach?
Please immediately contact your local stranding network or local authorities to report a live or dead stranded dolphin:
- For the Southeast Region, call 877-WHALE HELP (877-942-5343).
- Do not touch the dolphin.
- Don’t allow pets to approach the dolphin.
- Observe the animal from a safe distance of 100 yards (safe for you and the animal).
What should people do if they witness harassment or any marine mammal violation in the water or on the beach?
To report violations please contact NOAA’s Office of Law Enforcement at (800)853-1964.
What is the Unusual Mortality Event Contingency Fund?
MMPA section 405 (16 USC 1421d) establishes the Marine Mammal Unusual Mortality Event Fund, describing its purposes and how the public can donate to the fund. According to the MMPA, the fund “shall be available only for use by the Secretary of Commerce, in consultation with the Secretary of the Interior:
- To compensate persons for special costs incurred in acting in accordance with the contingency plan issued under section 1421c(b) of this title or under the direction of an Onsite Coordinator for an unusual mortality event.
- For reimbursing any stranding network participant for costs incurred in preparing and transporting tissues collected with respect to an unusual mortality event for the Tissue Bank.
- For care and maintenance of marine mammal seized under section 1374(c)(2)(D) of this title.”
The National Contingency Plan for Response to Unusual Marine Mammal Mortality Events outlines the types of expenses that are reimbursable under the fund and the process for requesting reimbursement.
How can deposits be made into the Unusual Mortality Event Contingency Fund?
The following can be deposited into the fund:
- Amounts appropriated to the fund.
- Other amounts appropriated to the Secretary for use with respect to UMEs.
- Amounts received by the United States in the form of gifts, devises, and bequests under subsection (d) of section 405(d) of the MMPA.