A seal pup can look healthy and still carry nerve damage subtle enough to doom it once it is back in the ocean. Researchers at Texas A&M's veterinary college and their partners have built an exam to catch that kind of damage, and are using it to ask whether mercury absorbed before birth is to blame.
The work, described Monday by the Texas A&M College of Veterinary Medicine and Biomedical Sciences, is led in part by Dr. Todd O'Hara, a toxicologist on the college's faculty whose team has followed pollutants in marine mammals, and the fish and other animals they eat, along the Pacific coast between Alaska and Mexico.
Mercury that starts in the womb
Mercury builds up as it moves from small prey to the predators that eat them, so seals, sea lions and other fish eaters can end up with high doses. Mothers can also pass it to their young during pregnancy and nursing.
In one earlier study with O'Hara as a co-author, young Steller sea lions from the far western Aleutians in Alaska had higher mercury readings, plus more PCBs and DDT, a pesticide banned for decades, than adult females or sea lions elsewhere. Levels varied from place to place, which the team links to differences in what the mothers ate.
A neurological exam built for flippers
Finding a contaminant does not prove it is causing harm, and checking a seal's nervous system is hard. Standard exams are written for dogs, cats and horses, not animals with flippers, thick blubber and tiny external ears.
So the researchers teamed up with The Marine Mammal Center, a rescue hospital in Sausalito, California, on an exam made for harbor seal pups. Veterinary neurologist Dr. Chrisine Thomson led the evaluation of 45 stranded pups the center admitted during a two-year span. The finished exam has 26 checks suited to how seals move and behave and takes under 12 minutes.
It has already helped sort out cases that only looked toxic. Some pups with odd neurological signs turned out to have an ear infection, a serious brain defect present from birth, or malnutrition.
