MYRTLE BEACH, S.C. - For many people drawn to the ocean by warmer water each year, sharks are the last thing they want to see. But for researchers from Coastal Carolina University who make the annual trek to the coastal waters off Georgetown County, finding healthy sharks are essential.

If shark or stingray populations are declining, it could indicate problems for other species, said Dan Abel, associate professor of marine science at Coastal Carolina University.

"Most sharks are the top predators in the their ecosystem," Abel said. "If the sharks don't do well and populations are declining, it's possible the health of the entire ecosystem is likewise declining."

The Coastal Carolina professors and students go out into the waterways several times a week from May through November. They catch and release sharks and stingrays so they can monitor their movements and fluctuating populations.

The information has been gathered for the past four years and shared with the National Marine Fisheries Service, which uses the it to update its management plan for sharks off the East Coast, Abel said. If the local shark population is not carefully managed, an unpredictable ripple can go through an entire ecosystem, Abel said. Abel said if sharks aren't around to feed on large fish, those fish in turn eat more smaller fish, which in South Carolina can lead to large populations of sea trout or red drum and a corresponding drop in smaller fish important to the ocean environment.

"On the other hand, if large sharks such as tiger sharks are declining, there may be more blacktip sharks, which are among their prey," Abel said. "These black tips may compete with commercial and recreational fishers for fish like trout and drum. The result is that the whole system may be out of balance.

Abel said in such a scenario, more blacktips could mean more shark bites for humans.

The study focuses on Winyah Bay, one of the largest estuaries in the Southeast; North Inlet, a pristine estuary surrounded by a nature preserve; and, Murrells Inlet, which is surrounded by development and has runoff pollution issues.

A similar study in Chesapeake Bay has been conducted since the 1970s and has led to some sharks being named as protected species, said Jack Musick, head of vertebrate ecology at the Virginia Institute of Marine Science.

"Most shark species are vulnerable to overfishing and stock collapse," Musick said. "You can drive their populations down, so it is important to keep a watch on those populations."

The two dominant species of sharks in Georgetown County waters are sandbar sharks, which grow to about six feet, and Atlantic sharpnose, much smaller at less than three feet. Both species use local estuaries as nursery grounds, Abel said.

In the past four years, the Coastal Carolina study team has caught about 500 sharks. The study needs to continue for another five years to determine whether the shark populations are holding steady, Abel said.