The cause of gull deaths near the Port of Tacoma last month likely poses no risk to human health according to preliminary lab results, but more tests are underway to determine the source of the die-off.
“Based on what we know so far, water pollution or contamination is highly unlikely and there is little or no risk to human health,” said Dr. Katie Haman, a veterinarian for the Washington Department of Fish and Wildlife (WDFW), which is investigating the incident.
Port of Tacoma workers first reported Jan. 22 that at least 30 gulls were found dead or dying in and around Commencement Bay. The birds were all glaucous-winged gulls or glaucous-winged/western gull hybrids, some of the most common gulls on the West Coast.
At least a dozen more dead gulls were reported by the public through Feb. 5, and 31 sick gulls showing signs of weakness and/or paralysis were taken to state-licensed wildlife rehabilitation centers.
No additional sick or dead birds have been reported in the area since then.
WDFW biologists collected six of the dead gulls and sent them to the Washington Animal Disease Diagnostic Laboratory (WADDL) at Washington State University in Pullman for testing. Another nine gull carcasses were sent to the U.S. Geological Survey’s National Wildlife Health Center (NWHC) in Madison, Wisconsin.
Haman reported initial lab results showed inflammation of the intestine and liver, but bacteria could not be cultured from those lesions, making it difficult to determine the cause. Initial lab work ruled out avian influenza virus and avian cholera, and standard screening at wildlife rehabilitation centers ruled out lead poisoning.
WDFW wildlife biologist Emily Butler noted that crows, waterfowl and other birds in the area were not affected – only the two species of gulls initially identified in the die-off – so water pollution or contamination is highly unlikely.
Marine algal toxins are also an unlikely cause because no other affected animals were found, but testing for them is underway at a National Oceanic and Atmospheric Administration (NOAA) lab.
Haman said additional lab tests are also looking for botulism toxin, even though the gulls’ symptoms don’t perfectly match what would be expected from such toxicity. Given the scavenging nature of gulls, they may have been exposed to the bacterial toxin from contaminated food sources.
Testing is also underway for heavy metals and viruses.
All final lab results are expected later this month.
Twenty-five of the 31 sick gulls were taken to the Progressive Animal Welfare Society (PAWS) in Lynnwood. Other gulls went to Puget Sound WildCare, Fair Isle Animal Clinic, and West Sound Wildlife Shelter. At last report, 20 of the gulls were still alive and showing signs of moderate improvement with supportive care.