Efforts to restrict the shark-fin trade -- which is now illegal in four states and has prompted legislation in at least six others -- have stirred a noisy public debate about how best to protect a top ocean predator whose numbers are shrinking.

While the United States boasts some of the world's toughest restrictions on shark fishing, requiring sharks be brought in with their fins attached, proponents of the measure argue more needs to be done to stem the decline of sharks.

"This is everyone's problem," said Eric Luedtke, a member of the Maryland House of Delegates, which is considering banning the sale and trade of shark fins, an Asian delicacy, much to the ire of some fishermen and restaurant owners.

Luedtke noted that large sharks off the East Coast have declined by 90 percent compared with historic levels, leading to an explosion in the Chesapeake Bay's cownose-ray population, which in turn wiped out some oyster beds.

"The reality is sharks don't recognize state boundaries; they don't recognize international boundaries," he said. "What's bad for oceans elsewhere is bad for oceans here."

But some Asian-American businesses that serve shark's fin soup, as well as fishing operators who catch sharks legally, oppose the bans, which went into effect in Hawaii in 2010 and in California, Washington and Oregon last year after receiving wide bipartisan support.

A group representing Asian-American shark-fin dealers, restaurateurs and grocers will argue in the California Superior Court in San Francisco next month that the ban is unconstitutional because the federal government has ultimate authority over interstate commerce and the state is not compensating them for the economic loss.

The fin trade is the top intentional driver of shark deaths worldwide -- killing between 26 million and 73 million sharks annually -- because their cartilage is used to make noodles for a soup served at weddings and business meals. Millions of sharks also die each year when they are caught accidentally in gear targeting other species.

In many ways, the push to target shark fins is modeled on the successful effort to outlaw raw ivory imports into the United States in 1989, a year ahead of a global ban on African elephant ivory. In both cases, according to Beth Lowell, campaign director of the international group Oceana, "It's the product which is driving the unsustainable trade of a species. If we can impact the trade of the product, we can have a difference outside the U.S. as well."

Although the United States was a major importer of elephant ivory, it accounts for less than 1 percent of the global shark-fin trade.

Maryland's secretary of natural resources, John Griffin, has joined coastal business groups, including fishing operations, restaurants and hotels, in opposing the Maryland measure out of concern it will restrict the local shark catch.

In a statement, Griffin said that while the administration of Gov. Martin O'Malley, a Democrat, shares the sponsors' goals, "We feel that the bill in its current state will hurt the honest Maryland commercial fisherman who already abides by the law and humanely lands sharks whole. As the bill stands, watermen will still be allowed to land sharks, but the fins will have to be wastefully discarded later in the process."

Rebecca Regnery, deputy director of wildlife for Humane Society International, said her group and others are targeting the shark-fin trade in states with major ports and with large Asian-American populations, not the overall practice of shark fishing. A bill is pending in the New York legislature, she said, and activists are concerned more shark fins could flow into other states if it passes.

"We think that closing down the big ports and places with large Asian populations will end U.S. involvement in the fin trade, to a large extent," Regnery said.

Legislators have tried to enact bans in Virginia and Florida but failed largely because of opposition from fishermen. Similar bills are pending in New Jersey and Illinois. Advocates are also eyeing Delaware, Nevada and Texas.

The shark-ban lobby represents an eclectic coalition and varies depending on the state: Distance ocean paddler Margo Pellegrino has joined the advocacy group Shark Stewards in New Jersey, while the National Aquarium in Baltimore is one of the major proponents for the Maryland bill.

Peter How, president of the Asian American Restaurant Association, estimated shark's fin soup constitutes between 2 and 3 percent of his members' sales.

"Nevertheless, the shark's fin soup can be replaced by dishes with other ingredients or substitutes out of environmental concern," How wrote in an e-mail. "It is just a matter of time for a full transition. After all, our culture has been changing along with the history for social needs."

Robert Hueter, who directs Mote Marine Laboratory's Center for Shark Research, said people need to keep in mind that banning U.S. fin imports will not address all the threats sharks face, especially since the bulk of the demand is in Asia.

"In and of itself, shark's fin soup is not the enemy," Hueter said. "If we could wave a wand tomorrow and end the fin trade it would reduce the worldwide shark mortality. The more important question is, would it reduce it enough?"

While it remains unclear whether Maryland's proposal will become law, the flurry of activity may prompt federal lawmakers to take action.