Indian River Lagoon dolphins are dying due to pollution and fishing gear
Sometimes, they just take the bait. Other times they are tangled in blue or other shades of braided fishing line.
A new study by the Hubbs-SeaWorld Research Institute finds that many bottlenose dolphins in the Indian River Lagoon choke on our lines, bait, and other fishing gear, or die tangled in the line. More people die from diseases exacerbated by pollution in the lake.
Their paper was recently published in the journal Wildlife Disease.
Like manatees, bottlenose dolphins were already emaciated and immunocompromised due to lack of food in the Indian River Lagoon. Years of toxic algal blooms that smothered the seagrass bed have exposed the fundamental fish underpinnings of the lake’s food web.
What did they find?
From 2002 to 2020, 790 bottlenose dolphins were reported to have stranded (alive or died) or needed intervention within the lagoon.
Most of them died in the summer months.
Inflammatory disease and trauma were the most common causes of death. Pneumonia and other respiratory diseases were especially common.
Was that unusual?
“It is common for young animals to develop pneumonia,” said Wendy Nock, a Hubbs-SeaWorld research scientist and lead author of the study.
But studies in recent years have found that lake dolphins are more susceptible to infection because their immunity is compromised by pollution and toxic algae blooms.
Why is the immunity of lake dolphins suppressed?
Scientists aren’t 100% sure but pollution and excess algae are part of the reason. A 2020 study found that algal toxins 1,000 times more deadly than cyanide linger at trace levels in the livers of bottlenose dolphins in the lake, and remain there even when the algae do not bloom.
The same type of algae is thriving this summer in the lake. It’s the same algae that glows bright blue like fairy dust when stirred up at night. The poison it emits is called saxitoxin.
What are the other leading causes of death?
Trauma accounted for 36% of dolphin strandings in the lagoon. Of those deaths resulting from trauma, 58% were caused by human activity.
The majority of trauma cases were caused by entanglement, fishing gear, ingestion of other debris, or propeller strikes.
Natural trauma, such as shark bites or interactions with stingrays, accounted for 12% of all cases, and trauma of undetermined origin was identified in 4% of cases.
How does fishing line harm dolphins?
Fishing line wraps around their flippers, sometimes to the point of amputation.
Braided line is the worst. Dolphins can swallow them, causing them to suffocate or become entangled.
“It causes severe tears in their appendages,” Nock said.
How many dolphins live in the Indian River Lagoon?
The dolphins that live in the Indian River Lagoon spend most of their lives there. Scientists estimate that the number of bottlenose dolphins is about 1,000 from Mosquito Lake to Jupiter.
NB; Avoid using exact numbers for estimates, guesses, etc
Where in the Indian River Lagoon do dolphins appear to be most at risk?
Banana River Lake in Brevard County, where researchers found that human activity is the number one cause of death.
“The fauna in that area is not very good,” Nocchi said. “Many of them, if not all of them, are thin to the point of emaciation.”
“We’ve had a lot of entanglements this year,” she added, referring to the dolphins found wrapped in fishing line. “We’ve had a lot of calves (tangled in fishing line) this year. They don’t necessarily know to be careful.” Calves from the same mother end up entangled several times, after the mother leads them to foraging areas that contain a lot of fishing lines in the water.
“We see repeat offenders,” Nock said of the calves. “It’s become a really big problem.”
Where do you call if you see a struggling dolphin or other wildlife?
Florida Wildlife Alert Hotline: (888) 404-3922.