Harbor seal species profile

Harbor seals were hunted from the 1870s to 1970s until they were protected in the United States by the 1972 Marine Mammal Protection Act and in Canada under the 1970 Marine Mammal Regulations in the Fisheries Act. The inland Washington harbor seal stock is estimated to be over 12,000, while the Strait of Georgia sustains approximately 39,000 harbor seals. Key threats include human disturbance, habitat degradation, loss of prey, and interaction with fishing gear and boats.

Last month's federal authorization to kill more than 700 sea lions to protect salmon runs along the Columbia River is prompting discussions of similar actions for harbor seals in Puget Sound. But experts say the situations are very different with many unanswered questions. 

As wildlife managers work to recover Puget Sound’s diminished Chinook population, a proposed white paper is expected to review the impacts of some of the salmon's chief predators. The study would include a section on potential management of seals and sea lions, prompting open discussion of a long taboo subject: Could officials seek to revise the Marine Mammal Protection Act — or even conduct lethal or non-lethal removal of seals and sea lions in some cases? Such actions are hypothetical, but we look at some of the ongoing discussions around the issue as prompted by a new resolution from the Puget Sound Leadership Council. 

Increased consumption of Chinook salmon by seals and sea lions in the Salish Sea “could be masking the success of coastwide salmon recovery efforts,” according to a new study published in the journal Scientific Reports. Endangered resident orcas are said to be declining in part due to a lack of available Chinook, the orcas' preferred prey.

A new study shows that increased populations of seals and sea lions are eating far more of Puget Sound’s threatened chinook than previously known, potentially hampering recovery efforts for both salmon and endangered killer whales. 

Scientists say Puget Sound’s salmon are dying young and point to low growth rates in the marine environment as a possible cause. In part one of this two-part series, scientists consider threats facing young salmon in the open waters of Puget Sound.

Harbor seal numbers were severely reduced in Puget Sound during the first half of the twentieth century by a state-financed population control program. This bounty program ceased in 1960, and in 1972, harbor seals became protected under the federal Marine Mammal Protection Act and by Washington State.

Occasionally, our magazine includes reports and essays from guest writers on the subject of Puget Sound ecosystem recovery. Biologist and author Eric Wagner has this look at an ongoing harbor seal survey at the mouth of the Stillaguamish River. Wagner says the study hinges on a basic question: Who is eating the salmon? 

A 2021 paper in the journal PLoS ONE describes a non-traditional approach to estimating the size of three harbor seal management stocks in the inland waters of Washington using aerial line-transect surveys and tagging data.

An article published in the Journal of Wildlife Diseases in 2021 describes trends in birth defects among harbor seals in the Salish Sea from 2003 to 2019. The results suggest a level of congenital disease in this harbor seal population that is important for continued monitoring.

An article published in the Journal of Wildlife Diseases in 2021 describes research documenting injuries among harbor seals in the Salish Sea caused by boat propeller strikes. The number of strikes increased significantly between 2002 and 2019, as did vessel traffic.

Harbor seals and harbor porpoises in the Salish Sea are showing a relatively high presence of antibiotic-resistant bacteria. A 2021 paper in the journal Oceans suggests that these findings may indicate a wider problem among other species in the region.

A study published in Marine Mammal Science in June 2020 followed the movements and behavior of rehabilitated harbor seal pups after being released into the Salish Sea. The results suggest that although their movements differ from wild pups that have been weaned, the rehabilitated pups do successfully make the transition.

Tiny bone samples show that seals alter their diets as conditions change. The findings could help scientists understand whether seals are contributing to local salmon declines.

A 2020 paper published in Frontiers in Marine Science describes details of the fungal disease Mucormycosis which has caused the death of harbor porpoises, harbor seals and one orca in Puget Sound in recent years. The authors discuss the implications for local marine mammals, specifically the endangered southern resident killer whale population.

A 2020 article in the journal Frontiers in Marine Science looks at harbor seal stranding and necropsy findings in the San Juan Islands to assess age-related stranding trends and causes of mortality. The harbor seal (Phoca vitulina richardii) population in the Salish Sea has been at equilibrium since the mid-1990s. This stable population of marine mammals resides relatively close to shore near a large human population and offers a novel opportunity to evaluate whether disease acts in a density-dependent manner to limit population growth.

A 2019 article in the Journal of Wildlife Diseases looked at trace element concentrations of heavy metals in the livers of harbor seals that died and stranded in the San Juan Islands. The study indicated exposure to trace elements (naturally occurring, human-introduced, or both) in the Salish Sea; however, the study reports that trace element toxicity is not a major threat to harbor seal health.

A 2014 paper in the journal PLoS ONE examines differences between foraging behavior of harbor seals based on haulout site locations, seasons, sexes and times of day. The authors hypothesize that these factors may help explain the variability in diet among harbor seals observed at different haul-out site groups in the Salish Sea. 

A 2017 paper in the journal Aquatic Mammals reports that harbor seals in the Salish Sea are less concerned about predators when they become habituated to humans. 

Vessel traffic is increasing in the Puget Sound region. A 2017 article in the journal Aquatic Mammals looks at the potential impacts that increasing vessel disturbance may have on resident harbor seal populations and how future management decisions may need to look at variable buffer zones related to level of human activity.

New, smaller acoustic tags will allow scientists to track steelhead migrations in Puget Sound in ways that were once impossible. Will they provide answers to the mysterious decline of these now-threatened fish? 

This article describes the first known case of conjoined twins in a harbor seal. The case was documented in the Salish Sea region where harbor seals are often used as indicators of contaminant levels. However, researchers say their findings do not support that this anomaly was due to any common contaminants and hypothesize that the twinning was caused by disordered embryo migration and fusion. 

A 2015 article published in the Marine Ecology Progress Series identifies intraspecific differences in diet between harbor seals in the Salish Sea, suggesting implications for marine reserve management. 

A 2014 article in the journal Northwestern Naturalist shows how Harbor Seal tissues can reflect regional and temporal trends in contaminants in Puget Sound.

This paper discusses the dietary habits of harbor seals (Phoca vitulina) in two estuaries in Puget Sound.

This paper discusses Brucella pinnipedalis infections in harbor seals (Phoca vitulina) in Washington state and transmission to humans and other wildlife. The disease poses a threat to endangered populations and may be exacerbated by organic pollutants.

A master's thesis prepared at Western Washington University discusses the impact of harbor seals on fish stocks in the San Juan Islands, where the seals are a year-round predator.