PADRE ISLAND NATIONAL SEASHORE, Tex. — It is nesting season here, and just offshore, Kemp’s ridley sea turtle No. 15 circles in the water before dragging herself onto the sand to lay another clutch of eggs.

The sea turtle, affectionately nicknamed Thelma by a National Park Service employee, has already beaten some terrible odds. Still in the egg, she was airlifted here from Mexico in the years after the 1979 blowout of the Ixtoc 1 rig, which spilled millions of gallons of oil into the Gulf of Mexico and covered the turtles’ primary nesting place.

Now Thelma and others of her species are being monitored closely by worried scientists as another major oil disaster threatens their habitat. Federal officials said Tuesday that since April 30, 10 days after the accident on the Deepwater Horizon, they have recorded 156 sea turtle deaths; most of the turtles were Kemp’s ridleys. And though they cannot say for sure that the oil was responsible, the number is far higher than usual for this time of year, the officials said.

The Deepwater Horizon spill menaces a wide variety of marine life, from dolphins to blue crabs. On Tuesday, the National Oceanic and Atmospheric Administration expanded a fishing ban in the gulf because of the spreading oil. But of the endangered marine species that frequent gulf waters, only the Kemp’s ridley relies on the region as its sole breeding ground.