Treaty tribes and partners are collaborating to answer a question essential to marine mammal management: How many salmon are being eaten by seals in Puget Sound and Hood Canal?
The Pinniped Predation on Salmonids Project, a partnership consisting of the Port Gamble S’Klallam and Nisqually tribes, Washington Department of Fish and Wildlife (WDFW), National Oceanic and Atmospheric Administration (NOAA) and the nonprofit Long Live the Kings (LLTK), has been collecting data over the past year to quantify abundance, movements and diets of seals in the Dosewallips, Duckabush and Nisqually river estuaries. The team also is working with the Stillaguamish Tribe to compare the results of this study with similar work in the Stillaguamish River estuary.
Seals are one of several pinniped species native to Washington. Their populations have rebounded significantly since the federal Marine Mammal Protection Act of 1972, said Megan Moore, a NOAA research fisheries biologist. This population growth has led to increased consumption of salmon and steelhead listed as endangered or threatened under the Endangered Species Act, including Puget Sound chinook and steelhead, and Hood Canal summer chum.
“This is the first time an intensive study investigating both pinnipeds and salmon has occurred simultaneously, focusing on the behaviors of the pinniped population, prey abundance and seasonality of salmon in their diet,” said Joy Lee Waltermire, senior fisheries biologist for LLTK. “It also is the first time a thorough pinniped population abundance has been completed using drones throughout the year.”
The partners are all trying to answer the same question, said Casey Clark, lead marine mammal researcher in WDFW’s wildlife program. Which species and age classes of salmon are being eaten by seals?
The answers will help natural resources managers understand and quantify predator-prey interactions, information that is vital to regional fisheries management decisions.
Studying seal habitat, diet
Researchers first need to understand how many seals are using the estuaries and how likely they are to be on shore and visible during project surveys. Monitoring techniques included attaching a transmitter tag on the hind flippers of seals to collect location information via satellite, reporting hourly how much time the animal is on land versus the water. Drone surveys were conducted twice a month to count seals hauled out at the estuaries.
Nearly 4,000 scat samples from the three estuaries and Stillaguamish River will be analyzed to get a clear picture of the seal diet at each location, Clark said. Prey remains, including fish bones and eye lenses, will help scientists determine the species and ages of salmon seals ate during the study. Additionally, DNA in the scat will provide information about the proportion of a seal’s diet that was made up of salmon, as well as the identity and sex of the seal.
“Those two pieces of information are going to be really valuable because there are definite sex differences in what the animals eat,” Clark said. “If males eat more salmon and females eat less salmon, and we learn that a site is used more heavily by males, this will help us interpret the impact to salmon.”
Using salmon to track seals
The other part of the research is understanding the habitat that seals and salmon share. The Port Gamble S’Klallam Tribe, NOAA and LLTK have been studying juvenile salmon survival at the Hood Canal Bridge for more than a decade, during which it became apparent that seals use the floating bridge to corral and prey on juvenile salmon, said Hans Daubenberger, senior research scientist for the tribe.
“It made us wonder, are there other places in Hood Canal or Puget Sound where pinnipeds are having these outsized impacts on juvenile salmon?” he said. “Addressing this issue is really important to the tribe in terms of trying to get back to sustainable harvest opportunities for tribal members.”
Using telemetry, two populations of steelhead and one population of chinook were tagged with transmitters that were read by receivers placed throughout rivers, estuaries, Hood Canal, Puget Sound and Strait of Juan de Fuca. The data includes date and time of detection so scientists can track fish migration and identify potential patterns of predation. Additionally, steelhead smolts from the Duckabush River were tagged with transmitters that track movement and detect temperature, telling scientists when a predator has consumed a tag.
The team will spend 2026 processing, analyzing and synthesizing the data collected, and hopes to have results available in about a year.
Above photo: Seals are seen hauled out in the Duckabush estuary, photographed during a drone survey in August. Washington Department of Fish and Wildlife, MMPA/ESA Permit #22678. Story: Tiffany Royal.
