UF Researchers Search For Ways To Save Sharks From Multiple Threats

May 20, 2003

GAINESVILLE, Fla. — Swimmers kicking off the summer beach season this weekend may fear sharks, but in some ways the giant predators face greater dangers than humans, says a University of Florida shark expert.

“Memorial Day weekend is the first major holiday weekend of the year for people entering the ocean, and it’s almost inevitable that we’re going to have a few nips,” said George Burgess, an ichthyologist who directs the International Shark Attack File housed at UF.

“We need to understand that there are millions of people spending a lot of time in the water doing the kinds of things that are provocative to sharks – kicking, splashing and screaming – in an area that many species of sharks call home,” he said.

The tide has turned against sharks because they and their relatives – skates and rays – are seriously threatened by overfishing, loss of habitat and other man-made intrusions, causing their numbers to decline dramatically, Burgess said. The dusky shark population is estimated to have declined by 80 percent along the U.S. East Coast, while other species have dropped by 30 to 50 percent, he said.

A large-scale effort is now underway to reverse that trend. The Florida Program for Shark Research at the Florida Museum of Natural History at UF is a member of a consortium of four shark research programs nationwide. The consortium received $1.5 million from the National Marine Fisheries Services earlier this year and is to receive another $1.9 million on July 1 to help plot a brighter future for sharks.

“Our research is largely devoted towards gaining a better biological understanding of the different species of sharks so that refinements in fishery management practices can be put into place to assure that not only we, but our children, will have these critters around in the future,” Burgess said.

One problem with current management policies is they assume all sharks are alike, when in reality each species has its own life history characteristics, Burgess said. Some reach sexual maturity faster or produce more young than others, while the length of the reproductive period varies from species to species, he said.

For example, the dusky shark, once a major player in the commercial shark industry, takes

three years to reproduce instead of the usual two, he said.

“The reproductive biology of the dusky shark is its Achilles Heel, certainly contributing to its marked decline,” he said. “By contrast, the sharpnose shark, a small species, reproduces every year and its population numbers are much higher. It’s this kind of variation from species to species that often grossly affects its vulnerability.”

Learning more about how the mother passes nutrients to the embryo in the uterus, and how these might be influenced by water quality and other environmental factors is one aim of the UF research team. Females of some species produce a milk-like substance the fetus may ingest or absorb, while those of other species circulate blood across a placenta wall, said Franklin Snelson, a biologist and another member of the UF team.

“We think of sharks as primitive animals, but nothing could be further from the truth,” Burgess said. “Because they’ve been around so long, they’ve developed very special adaptations unlike those found in other fish-like vertebrates. So their reproductive systems have developed in complex ways.”

Reproduction is one of many life history characteristics the UF team is studying in species important in the East Coast commercial shark fishing industry. The team also is analyzing growth rates by determining the time span represented by growth rings in sharks’ backbones, which are made of cartilage, and is trying to figure out what sharks eat by studying the fatty-acid composition of their livers.

“One of the problems of looking at the food habits of sharks has been that they often regurgitate what’s in their stomach as part of the physical labor of being caught by hook and line,” Burgess said.

Because environmental factors are critical to sharks’ well-being, the UF team also is tagging sharks and tracking their movements in response to man-made threats. One such project involves bull sharks, which use the shallow waters of the Indian River lagoon on Florida’s east coast as a nursery for their young. Their habitat is disappearing rapidly as encroaching boat traffic and human populations moving up the coastline destroy these marshes, he said.

The other three institutions that are part of the consortium are the Pacific Shark Research Center at Moss Landing Marine Laboratories at Moss Landing, Calif.; the Center for Shark Research at Mote Marine Laboratory in Sarasota; and the Shark Research Program at the Virginia Institute of Marine Science at Gloucester Point, Va.