LAGOON MYSTERY Why did animal deaths drop off? By Tyler Treadway tyler.treadway@scripps | 772-221-4219 Last year’s deluge of mysterious deaths of manatees, dolphins and pelicans in the Indian River Lagoon has subsided to barely a trickle. That in itself is another mystery: Conditions in the lagoon haven’t changed. Not to tempt fate by asking, but why aren’t the animals still dying? “It’s not like a switch was flipped back on and suddenly the lagoon environment became favorable for dolphins, manatees and pelicans again,” said Megan Stolen, research biologist at the Hubbs-SeaWorld Research Institute in Orlando. Researchers believe a change in environmental conditions in the lagoon, probably related to the loss of 47,000 acres of sea grass because of massive algae blooms, is the root cause of all the mysterious deaths. Because the different species have See ANIMAL, 4A A pair of dolphins are silhouetted by the setting sun as they surface while chasing schools of mullet in the Indian River Lagoon near Herman’s Bay in the spring. FILE PHOTOS Manatees swim through the water at the viewing area on the north side of the Vero Beach Power Plant. Pelicans dive for fish off Tombolo Point off Marina Square at the Stormwater Waterfront Protection Project for the Fort Pierce City Marina in the Indian River Lagoon in November. Article Continued Below See ANIMAL on Page A04 ANIMAL from 1A died in different ways, there are still lots of dots to connect. Figuring out why the deaths stopped could be a key to figuring out why they started. Its important to find the cause, or causes, behind these deaths, said Martine de Wit, a veterinarian at the Fish and Wildlife Research Institute in St. Petersburg. Manatees are endangered, and this large a number of deaths threatens the entire species. Second, we dont know how big an impact these deaths could have on the entire lagoon ecosystem. If it happened in the Indian River Lagoon, it could happen in other areas. And finally, these deaths are a signal that somethings wrong in the lagoon ecosystem, something that could potentially affect humans. Manatees In Brevard County, the hot spot for manatee deaths in 2013, a total of 245 manatees died last year, 161 from unknown causes. Through May this year, 46 manatees have died in the area, 26 of them from unknown causes. Now were looking at maybe one (dead) manatee a month that fits the definition of this phenomenon, de Wit said. They appear to be healthy, theyre eating well, but they die suddenly. The search for the cause continues, de Wit said, but I cant say were any closer. Two theories have fallen by the wayside. Researchers do not believe it was natural selection, killing off the weakest manatees. They also dont believe manatees that migrate through the lagoon were killed while year-round lagoon residents adapted and survived. I dont think this is a case of survival of the fittest because we had big, strong manatees dying, de Wit said. We identified some of the carcasses to see if they were resident or migratory manatees ... and it turned out they were a mixture of both. A Harbor Branch Oceanographic Institute research team last August announced it had isolated a toxin growing on seaweed in the northern lagoon that could be behind the mysterious manatee deaths. Gracilaria, a seaweed manatees began eating because of the sea grass loss, was found to contain toxic glycosides and symptoms caused by eating glycosides match those suffered by the manatees, Brian Lapointe, a research professor at Fort Pierce-based Harbor Branch, said at the time. Glycosides are still a very good possibility, Lapointe reiterated earlier this month. The cause could be related to the change in the manatees diet, de Wit agreed, but a specific killer toxin has yet to be discovered. Also, green sea turtles, which subsist primarily on sea grass, probably switched to eating seaweed without ill effects. Dolphins In 2013, a total of 78 bottlenose dolphins died from unknown causes in the lagoon, 43 of them in March through June. Through March this year, five dolphins have died in the lagoon. The numbers are particularly dramatic because only about 700 dolphins were living in the lagoon before the rash of deaths began. Were pretty confident the cause was some kind of environmental change rather than, say, an infectious disease, Stolen said. But we dont know how that change translated into dolphins dying. Unlike the healthy-looking manatees that died, all the dolphins killed by the mysterious cause were emaciated, super-skinny, Stolen said. It could have been a problem with the fish the dolphin eat, such as their number or distribution. Or it could have been a problem with the dolphins ability to catch prey. Spotted sea trout, the primary food source of lagoon dolphin, has all but disappeared from Titusville south to Sebastian, said Grant Gilmore, lead scientist at Estuarine, Coastal and Ocean Science in Vero Beach. He blamed the loss of 47,000 acres of sea grass in that stretch of lagoon because the beds are nurseries for young sea trout, providing them with the food and cover they need. Gilmore blamed the sea grass loss on massive algae blooms that shaded the sea grass, blocking sunlight and preventing the grass from photosynthesizing food. When you have a decline in sea grass, you have a decline in sea trout and a decline in dolphins, he said. Brown pelicans More than 300 brown pelicans died in the lagoon between Titusville and Sebastian last year, mostly in February and March 2013, according to best estimates. So far this year, no unexplained pelicans deaths have been reported. As with manatees and dolphins, researchers believe environmental changes in the lagoon brought on by algae blooms and the resulting loss of sea grass is a factor, said Jan Landsberg, research scientist at the fish and wildlife lab in St. Petersburg. Right now, we are only able to say some of the things it wasnt, Landsberg said. We at first suspected botulism (bacteria) because pelicans are prone to it. But it wasnt that, or West Nile virus or any of the other viruses we tested for. As with dolphins, pelican carcasses were emaciated and appeared to have died over several days. Like dolphins, pelicans are fish-eaters, but they tend to eat smaller fish and more species of fish than the sea trout dolphins consume. Other birds eating the same types of fish - ospreys and herons, for example - seemed just fine, Landsberg said. And wed go out and see a lot of pelicans that were OK right next to ones that were dead or dying. DEATHS FROM UNKNOWN CAUSES Manatees (Brevard County) 2013: 161 2014: 26 Dolphins (All lagoon) 2013: 78 2014: 5 through March Brown pelicans (Brevard County) 2013: More than 300 2014: 0 WHO TO CALL To report dead or injured manatees, dolphins and pelicans: Call: 888-404-FWCC (888-404-3922) Cellphone: *FWC or #FWC Be prepared to answer: Exactly where is the animal? Is it alive or dead? How long have you been observing it? What is its approximate size? Where is the nearest public boat ramp? How can you be reached for more information?
Posted on: Sun, 29 Jun 2014 09:03:47 +0000
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