(Daytona Beach News Journal)
Wednesday, February 8, 2012
Researchers say Indian River Lagoon bull shark nursery critical
BY DINAH VOYLES PULVER, STAFF WRITER
February 7, 2012 12:55 AM Posted in: East Volusia - Environment Tagged: Indian River Lagoon , sharks
A young bull shark is pulled from the waters of the Indian River Lagoon. (Florida Museum of Natural History | George Burgess)
Scientists studying the Indian River Lagoon, long considered one of the world's richest ecosystems, say new findings show the lagoon is a critical nursery for one of the ocean's top predators.
After reviewing 30 years of research and conducting new studies by catching and tagging live young sharks, one trio of scientists says the lagoon may be "the most significant bull shark nursery area on the U.S. Atlantic Coast."
While the average person may not be able to fathom why anyone would care about sharks, fisheries biologists say as an apex predator, the bull shark plays a key role in the food webs in the lagoon and the ocean.
"If things go south (in the lagoon), the population of bull sharks all up and down the United States gets affected," said George Burgess, director of the Florida Program for Shark Research at the University of Florida's Florida Museum of Natural History. "The ramifications could be huge."
While Volusia County leads the country in shark bites, Burgess, an international shark bite expert, said the blame for those frequent shark bites near Ponce de Leon Inlet shouldn't be placed on the bull shark.
Though larger bull sharks are often "one of the prime suspects" for the more serious attacks in Volusia and elsewhere, Burgess said most of the incidents in Volusia "tend to occur from smaller, fish-eating species that are presumably making mistakes in judgment."
The Indian River Lagoon is actually a cluster of three lagoons that stretch more than 150 miles along more than a third of Florida's east coast, from Ponce de Leon Inlet in Volusia County south to Jupiter Inlet in Palm Beach County. It includes Mosquito Lagoon in Volusia and Brevard counties, the Indian River and the Banana River.
The lagoon's health and water quality is vital for many species of wildlife, said Tobey Curtis, who co-authored the study while obtaining his master's degree at the University of Florida.
"A lot of people think about birds and fisheries for snook, tarpon and redfish, but don't realize how important it is to sharks," Curtis said.
The lagoon provides two things that are critical to the success of a nursery, for bull sharks as well as other species, Burgess said: abundant food and a degree of protection against predation by larger animals.
The food resources in the lagoon make it "very special," not just for sharks but for shrimps, crabs and any number of fish, he said. That includes "important commercial and recreational species, as well as the little unsung 97 percent that aren't highly esteemed as food fish but important as intermediary steps in the food chain."
"Each of these species has its own ecological niche to fill, and when you start to reduce or start to take away from that, it does throw off the balance, without question," said Doug Adams, a fisheries biologist for the Florida Fish and Wildlife Conservation Commission and the third and final author of the study.
The lagoon helps sustain larger offshore populations of other species, said Adams, who monitors fish populations in the lagoon and just offshore for the commission.
THE RESEARCH
Adult female bull sharks enter the lagoon via the two inlets in spring, give birth to their pups and then leave by fall, concluded the scientists, who monitored the movement of young bull sharks by tracking them using acoustic tags.
The museum also benefited from a boat donated for its research by a New Smyrna Beach couple, Chris and Wendi Peterson.
Curtis said he found it "very exciting to handle sharks."
The sharks were "quite small," less than 3 feet in length, Curtis said.
Because the pups are born right into the lagoon, "it's really kind of neat to see a very small version of what's going to become potentially a very large apex predator."
"When they're that size, they're pretty manageable," he said, "but they still have the attitude of a big one, even though they're pint-sized."
The researchers found that newborn and juvenile sharks seem to prefer shallow freshwater creeks that flow into the lagoon, creeks that have been historically degraded by human development. The researchers said that degradation may be having negative impacts on the young sharks and should make further restoration of water quality a "high priority."
They found a higher than average density of juvenile bull sharks in the northern end of the Indian River Lagoon and the northern end of Mosquito Lagoon during the spring, summer and autumn. They surmised the young sharks migrate south in the lagoon in the winter, returning to the north around March.
The scientists aren't yet certain how long the juvenile sharks remain in the lagoon before they head for the open waters of the Atlantic.
The news that the bull shark pups are so prevalent in the lagoon comes as a bit of a surprise to fishermen, who say they rarely see sharks.
SHARK ENCOUNTERS
Brian Clancy, an experienced guide who has fished in the lagoon for years, said he has never had an encounter with a bull shark.
Clancy said he's only heard of one person catching a bull shark, during tarpon season. He said the fisherman estimated it was about 100 pounds. He's surprised the dozens of clammers in the lagoon don't have shark encounters.
Sightings are not routine partly because the sharks are so elusive, said Adams, the state fisheries biologist. "They go kind of below the radar for most people, even for anglers and people who work on the water."
Even avid anglers may only catch a couple of bull sharks in a lifetime, Adams said.
Also, Burgess said, there just aren't that many bull sharks. Like other large shark species, scientists believe they suffered population declines in recent decades. And, in the ocean, they tend to live farther offshore as adults.
Witnesses in the water when a Winter Park man was bitten at New Smyrna Beach last fall said they thought the culprit was a bull shark that had been seen cruising the sandbar for mullet.
Burgess suspects that either a bull or a tiger shark was responsible for the death of a Martin County kite surfer in February 2010, but said it's difficult to tell the bite of the two large sharks apart, unless the shark leaves a tooth behind.
Adams said he has worked in the lagoon for more than 20 years, working with sharks repeatedly, and has never had a single negative reaction. He said he has never heard of anyone else having one, other than the occasional story of a fisherman losing a red drum on the line to a shark.
"For the most part, they don't want to have interactions with you," Adams said. "They do not approach people."
Adams describes sharks as "really cool." He and Burgess continue to conduct research in the lagoon, part of long-term efforts to protect the lagoon, its water quality and the submerged sea grass beds that provide the foundation of life in the lagoon.
State and local agencies have worked over the past couple of decades to try to improve the overall health of the lagoon.
"If you tweak something in the Indian River Lagoon," Burgess said, "it's going to have a reaction that might go into the Gulf of Mexico or it might go up as far north as North Carolina."
0 comments:
Post a Comment