Study: Population of great whites rebounding [Cape Cod Times, Hyannis, Mass. :: ]
(Cape Cod Times (Hyannis, MA) Via Acquire Media NewsEdge) June 13--CHATHAM -- Sightings of great white sharks in Cape waters is one indicator that the species is rebounding from the lows of 20 years ago, according to a National Marine Fisheries Service study released this week.
The study, which is based on historical data from 1800 to 2010, says there are signs that the great white shark population is recovering from what many believe was a sharp drop-off in the 1970s and '80s because of heavy commercial and recreational fishing.
The study, published Wednesday in the online journal PLOS ONE, was the first significant update on the status of the great white shark population in more than 40 years and shows that the ban on landing these sharks, enacted by the United States in 1997, has paid off.
"This is not a booming population," said Tobey Curtis, a NMFS fishery policy analyst and lead author of the study. "But these are optimistic signs for recovery."
The NMFS study did not involve searching the water for great whites, but sifting through more than 200 years of data resulting in 649 confirmed white shark reports from federal fishery observers, landings data, shark tournaments, research surveys, and commercial and recreational fishermen. Computer modeling was used to incorporate environmental information recorded at the time of the report, such as number of vessels fishing in the area, weather, water temperature and depth, to help determine relative abundance of white sharks.
The result was a broad-brush portrait of the species in the Northwest Atlantic, where more than 80 percent of sharks were found in water temperatures between 57 and 67 degrees.
Most great whites spend the winter in Florida. Some head north in the spring, and they are most likely to be in the waters between New Jersey and Massachusetts in the summer months.
Since more than 60 percent of 1-year-old great white sharks considered in the study were off New Jersey and Long Island, that may be a vital nursery area.
But the study only shows trends. It does not say how many great white sharks might be out there, which is what those concerned with beach safety want to know.
Next week, state Division of Marine Fisheries shark researcher Greg Skomal will launch a research project to get an accurate estimate of how many great white sharks enter Cape waters each summer, lured here by the burgeoning gray seal population. It's the most frequent question he is asked by the public and the media, he said.
"We think that what we are seeing is more and more animals each year as they learn about (the seal colony)," said Skomal, who was also a co-author on the NMFS paper. "They may, or may not, stay, but at least they are pulling off the highway and coming into this rest stop."
Skomal's work will be what is known as a mark-and-recapture study that is widely used in estimating animal populations.
A spotter plane will find and direct his boat to great whites. Using a waterproof video camera, the crew will first try to identify the shark by the distinctive pattern of markings where the white underbelly meets the gray of the upper body. Scars and the fraying on the trailing edge of the dorsal fin also can aid in identification. Some of the sharks will be fitted with acoustic tags that give off a signal that is unique to each individual and can be picked up using a hydrophone at sea or by receivers tethered to buoys along the shoreline.
The ratio of how many get marked to how many are seen again ultimately provides that population estimate. The project will produce a catalog used to identify individuals in the future.
"If you get 10 percent of the population, that's a pretty good population size estimate," Skomal said.
The three- to five-year $30,000 project is funded by the local nonprofit Atlantic White Shark Conservancy and is the first of its kind for the Atlantic, Skomal said. The data ultimately may factor into determining a total population figure for the Northwest Atlantic.
Meanwhile, the methodology developed by federal fisheries scientists can be updated to provide an index for abundance going forward, researchers said.
Cami McCandless, a co-author on the NMFS study and a research fisheries biologist at the agency's Apex Predators Program in Rhode Island said more sophisticated data retrieved through satellite and tagging done by Skomal and others adds detail to the broad migrational patterns.
"The old paradigms are breaking down," Skomal said.
Lydia, a female shark tagged by Skomal and the shark research vessel and crew of OCEARCH, came north this past winter and headed off toward Portugal. Some scientists believe she may have been feeding on schooling fish in an area of the ocean once assumed to be a virtual desert.
"This is tearing down these very simple life-history patterns we thought existed for these animals," Skomal said.
Management measures for other fisheries, such as Florida's ban on gillnets, has helped great whites, Skomal said. The number of newborn and juvenile white sharks appear to be evidence that the species is producing many young fish that survive. That's important in a species that can live to more than 70, doesn't become sexually mature until 12 to 15 years old and has small litters.
He thinks that positive trend, in combination with fisheries regulations, means a bright future for sharks.
"I don't see anything changing the trajectory we are on," Skomal said.
(c)2014 the Cape Cod Times (Hyannis, Mass.)
Visit the Cape Cod Times (Hyannis, Mass.) at www.capecodonline.com
Distributed by MCT Information Services
[ Back To Technology News's Homepage ]