WASHINGTON Shrimp boats that fish in the Gulf of Mexico without the required turtle-excluder devices are killing more sea turtles than is allowed under the Endangered Species Act, the advocacy group Oceana said in a report Tuesday.

The organization based its new estimate of leatherback and loggerhead turtle deaths on federal fishery regulators' emails about periodic checks on the use of the turtle-excluder devices. The group obtained the emails under the Freedom of Information Act. If the memos capture a representative sample of the fleet, the group estimates that 4,874 loggerheads and 108 leatherbacks were killed in the nets last year.

"There are other types of fishing gear that can be dangerous to sea turtles, and there are other problems like oil spills and plastic pollution, but we think the greatest threat now is the shrimp trawl fishery," said Elizabeth Griffin Wilson, senior manager for marine wildlife at Oceana.

Shrimp boats that trawl on the seafloor have been required to have turtle-excluder devices for nearly 20 years. But Oceana said the problem of sea turtle deaths remained unsolved because of noncompliance, poor enforcement and exemption from the rule for some types of trawlers.

Since January, more than 423 injured or dead sea turtles have washed up in Louisiana, Mississippi and Alabama, the National Oceanic and Atmospheric Administration reported last week. The number is consistent with last year, during the BP oil spill, but higher than in previous years.

"It's clearly a problem because there are way too many dead turtles," said C. David Veal, the executive director of the American Shrimp Processors Association in Biloxi, Miss.

The fishing industry blames the oil spill, but sampling by federal officials shows compliance with turtle-excluder device rules is inadequate, Veal said.

"Over time, apparently, we've gotten a little lax at that because the numbers show there's a problem," he said. Still, he said, the data available so far don't make it clear that the shrimp industry is the major culprit.

Oceana examined memos from federal fisheries officials who checked on the use of the devices in Mayport and Fort Myers, Fla., Biloxi, Miss., and ports in Texas and Louisiana, plus state inspections in Georgia. The memos showed that of 76 vessels checked in the Gulf of Mexico, 17 percent had no turtle-excluder devices or the devices were blocked intentionally.

In Mississippi and Florida, none of the 22 vessels checked was in compliance with the rule. In Georgia, 47 percent of 30 vessels observed last year were in compliance.