Seabirds nesting in Puget Sound consume fish far more contaminated by long–lasting urban pollutants such as PCBs and flame retardants than seabirds feeding on the outer Washington Coast, according to a new study led by researchers at the Northwest Fisheries Science Center.
The study of rhinoceros auklet colonies in Washington state signals that seabirds feeding near urbanized estuaries and coastlines may accumulate the toxics known as persistent organic pollutants, or POPs, at levels that could jeopardize their behavior, reproduction and immune systems.
The diets of rhinoceros auklets in Puget Sound include roughly two to four times more POPs than diets of auklets on the Pacific Coast outside Puget Sound. Rhinoceros auklet carcasses salvaged as part of the study suggest that the same pattern extends to the birds themselves, with auklets from Puget Sound carrying much higher concentrations of PCBs than those from the outer coast.
"Rhinoceros auklet chicks in Puget Sound are eating the most contaminated fish, so they’re going to get a greater overall contaminant load during their first summer,” said Tom Good, a research biologist at the NWFSC and lead author of the study. “It certainly points to the potential of them having, if not lethal effects of pollution, then sub-lethal effects such as compromised immune systems."
The pollutants may in some cases accumulate to extreme levels in seabirds: One tufted puffin carcass from Puget Sound held POP concentrations nearly 10 times higher than rhinoceros auklets, rivaling pollutant levels in much larger and more voracious Puget Sound killer whales.
The study examined three colonies of rhinoceros auklets for exposure to POPs in their diets. The colonies included Protection Island in the inland waters of Puget Sound, Tatoosh Island at the outer tip of the Olympic Peninsula and Destruction Island off the Washington Coast. Birds typically return to the same colony and possibly feeding area year after year.
Researchers used "spotlighting" and surprise to sample the auklets’ meals. They sat in the seabird colonies at dusk and shined their headlamp beams on adult auklets landing nearby with bills full of fish. The startled auklets would typically freeze, drop their mouthfuls of fish and then run or fly off, leaving the fish for researchers to test for contaminants.
The researchers gathered samples only a few nights each year and varied their collection location in each colony to minimize effects on individual breeding pairs of birds.
The fish eaten by auklets varied between colonies but commonly included Pacific sandlance, Pacific herring, northern anchovy and salmon. Researchers calculated the POP exposure of auklet chicks in each colony through a “food basket” approach that accounted for the amount of each fish species in a colony’s diet and the concentrations of POPs in each fish species.
The results showed that the diet of Protection Island chicks exposed them to 4.5 times more PCBs and 4.5 to 7.5 times more flame retardants called PBDEs than those in the other two colonies. Scientists have so far not seen overt signs of adverse effects on the Protection Island birds, Good said, but continued monitoring should document them if they appear.
Among the most contaminated fish detected in the study were Chinook salmon. Three of 10 Chinook salmon from Protection Island exceeded PCB thresholds for adverse health effects on fish and two of the 10 carried concentrations of PBDEs associated with increased susceptibility to disease in yearling Chinook salmon.
One surprise was the elevated levels of POPs in salmon from the Destruction Island colony on the outer Washington Coast. Two of the three Chinook salmon from Destruction Island had PCB concentrations similar to fish from interior Puget Sound and other polluted sites. Those same fish also had the highest PBDE levels recorded in the study, far exceeding levels linked to increased susceptibility to disease.
The researchers suggested that the contaminated salmon collected from the Destruction Island colony may have originated from the Columbia River, another hotspot for contaminants in the Pacific Northwest.
Good said further research and monitoring would better gauge the effects of elevated POP exposures on locally breeding seabirds.