Wednesday, October 27, 2021

Dolphins Suffering Effects of ‘Dead Zone’ 

Even months after the end of the persistent red tide which affected much of Florida’s Gulf coast, its effects are still profoundly felt. Within the last several months, 177 dolphins have been reported dead between Collier and Pinellas counties. The National Oceanic and Atmospheric Administration (NOAA), has currently been monitoring two distinct Unusual Mortality Events – one originating from off the west coast of Florida and the other around the outflow from the Mississippi River.  

The bottlenose dolphin population in particular has been affected the most heavily, washing up on beaches across the Florida coast. While the root of the cause has yet to be determined the NOAA has identified a dead zone ranging 8,776 square miles in size off Florida’s coast, which has been present for more than a year 

In an interview, Dr. Erin Fougeres of the National Oceanic and Atmospheric Administration told Coastal Breeze News, “It coincided with the red tide bloom in Southwest Florida which ultimately ended up stretching into the Pinellas and Hillsborough area.”  

Dr. Fougeres works within the Protected Resources Division at NOAA, a branch responsible for the conversation of marine species under the Endangered Species Act. “We really started to see mortalities begin to pick up around July of 2018, Dr. Fougeres stated.   

The current mortality rate of dolphins within this particular region has increased above four times the average. This can be attributed to the aforementioned dead zone,” a low-oxygenated region of ocean is likely brought about as a byproduct of algal blooms, leaving this swath of water next to uninhabitable for marine life. “What we’re seeing now are less mortalities caused by acute red tide toxicosis,” Dr. Fougeres said, “So less mortalities are linked directly to the red tide and more indirect effects that could potentially be due to prey depletion.”  

As carnivores, dolphins naturally hunt fish as a major part of their diet, relying on the schools of fish to feed themselves and other members of their group. Yet as the red tide swept through large numbers of fish ended up dying, leaving a significant area without enough food to go around for the remaining dolphin population. Additionally, toxins left behind by the algae still remain within the fish even after the red tide dissipates – allowing for toxins to slowly build up in the liver of the dolphin and poison them over time. This means whatever food is left for the bottlenoses within these dead zones is unsafe to eat. Unlike most other dolphins the bottlenoses around Florida prefer to stay in a relatively small area during their entire lifetime, leading to a situation where many of these dolphins are stuck within an area of ocean unfit for life. 

Marco Island was lucky during the last bout of red tide, attests Bob McConville, a naturalist who works with the Dolphin Explorer Eco-Tour program out of the Rose Marina. “We have not lost any of our dolphins that we’re aware of to the red tide south of the Naples pier,” McConville states, attributing this to the island’s location along the side of Florida and the oceanic currents to sparing the local dolphin population. 

Although it is unusual to see bottlenose dolphins moving outside of their native environment during the red tide season McConville and his crew noticed peculiar behavior from the marine life. We saw some of the dolphins that we’ve identified in south Naples and behind Keewaydin Island coming down to the Marco River on the other side of the Jolley Bridge,” he recalls, “Dolphins are very smart. I think they figured out that the fish along the coastline were tainted and came down here.”  

It’s the longer term impacts we’re worried about,” said Fougeres, who asserts that NOAA is closely monitoring the situation in the Gulf and how the environment will be impacted looking into the future.  

“Every level of the ecosystem is affected,” McConville elaborates, “The sea grasses are wiped out, the animals feeding on those grasses are gone, the fish disappear, and that can be disastrous for the dolphins as well.”  

When a red tide occurs there are few ways one can help the dolphins directly, but for any dolphins or marine life one finds washed up on the beaches Fougeres advises, “The best way for people to help is to report any injured or stranded dolphins that they come across to the Marine Mammal Stranding Network who will send authorized and trained responders out. They can do that by calling 877-942-5343 and that’ll connect them to their local Stranding Network organization.” 

The Dolphin Explorer has recently begun to work in cooperation with NOAA as well as Rookery Bay National Estuarine Research Reserve to keep track of the dolphin populations in the area. In the case of deceased dolphins during a red tide event, McConville reminds residents to be vigilant;Take a picture of their fins and send it over to us so we can see if it’s a dolphin in our catalog or if it’s one that washed in from the Gulf so we can identify the severity of the event as far as the local population goes.”  

For any additional information of the dead zones, NOAA will be holding a teleconference to discuss their findings on Thursday August 1st at 1:30 PM EDT. The phone number is 1-888-324-9431 and the code HYPOXIA. Visit for further information. 

Courtesy OAA National Environmental Satellite, Data and Information Service.

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