LOS ANGELES (Reuters) - More than 300 sea birds, nearly 200 turtles and 19 dolphins have been found dead along the U.S. Gulf Coast during the first five weeks of BP’s huge oil spill off Louisiana, wildlife officials reported on Monday.

The 316 dead birds collected along the shores of Louisiana, Mississippi, Alabama and Florida -- plus 10 others that died or were euthanized at wildlife rehabilitation centers after they were captured alive, far outnumber the 31 surviving birds found oiled to date.

The raw tally of birds listed by the U.S. Fish and Wildlife Service as dead on arrival at wildlife collection facilities include specimens obviously tainted with oil and some with no visible signs of oil contamination.

But all are being counted as potential casualties of the oil gushing since April 20 from a ruptured wellhead on the floor of the Gulf because of their proximity in time and space to the spill, said Jay Holcomb, who directs a rescue center for birds in Fort Jackson, Louisiana.

The same is true of nearly 200 sea turtles found dead and dying along the Gulf Coast, and 19 dead dolphins verified in the region since the oil drilling blowout on April 20.

Tissue samples collected eventually will be analyzed to determine more conclusively if the animals were contaminated with oil from the BP spill.

Holcomb, director of the California-based International Bird Rescue Research Center, said mortality for sea birds, many of them in the midst of their breeding season, is expected to climb sharply, especially if hurricanes move into the region and sweep more oil ashore.

Veterinarian Heather Nevill (L) and rescue worker Deanene Birtell hydrate a Laughing Gull, rescued from oil contamination from the Deepwater Horizon spill, as they prepare it for transport from the Ft. Jackson Wildlife Rehabilitation Center in Buras, Louisiana May 23, 2010. REUTERS/Lee Celano

“The potential for this being catastrophic is right there because there’s a massive amount of oil in the water, and it’s still pouring out, and there’s a lot of nesting birds and a lot of birds using the coast,” he told Reuters. “If the tropical storms take that oil and move it, that’s when you’re going to see the real impact, I think.”

The size of BP’s disaster in the Gulf could eclipse the scale of the 1989 Exxon Valdez spill in Alaska’s Prince William Sound, in which an estimated 250,000 sea birds perished.

DIVING BIRDS HARDEST HIT SO FAR

The birds hardest hit by oil in the Gulf so far are those that feed by diving into the water for fish, including the Louisiana state bird, the brown pelican, removed last year from the U.S. endangered species list, and the northern gannet, Holcomb said.

But shorebirds, wading birds and songbirds will increasingly be put in harm’s way as more oil washes onto beaches and into marshlands.

Oil impairs the insulating properties of birds’ feathers, exposing them to cold and making it difficult for them to float, swim and fly. Chemicals in the petroleum also can burn their skin and irritate their eyes. They also end up ingesting the oil when they preen, damaging their digestive tracts.

Other wildlife at immediate risk in the Gulf are sea turtles and marine mammals.

To date, 209 sea turtles have been found dead or debilitated along the Gulf Coast, about double the number reported late last week, a tally that wildlife officials said then could be considered normal for this time of year.

The latest figure includes 194 that washed ashore dead and 12 that were found stranded alive, two of which later died in rehab, said Dr. Michael Ziccardi, a veterinarian and professor at the University of California at Davis who is overseeing sea turtle and marine mammal rescue teams in Louisiana.

Three remaining turtles in the latest tally were found heavily oiled at sea but have survived, he said. Those three are the only ones with outward signs of oil contamination.

Necropsies, the animal equivalent of autopsies, have been performed on 40 turtle carcasses found intact, and a majority of the findings pointed to drowning or the aspiration of bottom sediments as the cause of death, Ziccardi said.

Although the results are “inconsistent with oil exposure as a primary cause of death,” lab tests of tissue samples are still pending, so less visible factors remain to be determined, he said.

Nineteen dolphin deaths also have been confirmed since the spill began, but none of those animals showed any obvious external or internal signs of oiling, Ziccardi said.