In conclusion

1. What are the biggest threats to the health of Puget Sound?

We reviewed eight assessments of threats relevant to the Salish Sea ecosystem. While each presents a unique list, there is considerable overlap and consistent high ranking of development, climate change, invasive species, pollution, and shoreline modification. Species harvesting was also highly ranked and should be priority topics for future synthesis.

In just over a century, the human enterprise in the Salish Sea Ecosystem has had tremendous impacts. The human footprint has taken roughly half of the forest and wetlands, impounded 37% of the drainage, removed 1000 km of natural shoreline and altered weather patterns such that entire glaciers have been lost. Simultaneously, human activities have introduced toxins, endocrine disruptors, and at least 700 non-native species in the system. The combined impacts of these changes and their current and future interactions in an environment substantially warmed by anthropogenic energy demands are profound and wide reaching.

Conversion of land from forest to human settlements has transformed the watersheds that feed the Salish Sea to the detriment of terrestrial, freshwater, and marine ecosystems. The importance of linkages between terrestrial and aquatic systems cannot be overstated. Furthermore, the interaction between factors such as modifications to the landscape and climate change can enhance declines of habitats (e.g., salmon habitat).

2. What are key lessons learned?

In an effort to boil down the information in this chapter and highlight the most important lessons learned, we selected key pieces of information where there was a significant weight of evidence to support the observation, there were good data and high certainty, impacts were wide ranging impacts in the ecosystem or were derived from multiple threats, and where good information existed to characterize threats (please see specific sections for references).

Climate change If climate changes as predicted, the following impacts will likely occur:

  • The Climate Impacts Group predict average temperature rise in the Pacific Northwest of 1.1°C.
  • The combination of warming temperatures and decreased snow to precipitation ratio will affect snowmelt and the region’s water supply will be affected.
  • Stream temperature will be less hospitable to salmon.
  • Sea surface temperatures in Puget Sound will increase by ~ 6°C, causing an increase in algal blooms and hypoxic events.
  • Acidification of Puget Sound waters is cause for concern for organisms at the base of the food chain supporting higher tropic levels.

Invasive species

  • Of the 700 species introduced/established in and around Washington State, the council identified 50 priority species/guilds based on these having highest impacts to the system.
  • Trans-Pacific vessels had higher diversity of non-native species, and densities of non-natives were 100-200% greater in domestic ballast water. Considering that a variety of biological and physical factors affect an invader’s success, both foreign (high diversity) and domestic (high density) sources of ballast water have high potential to result in successful invasions of the Sound.
  • In the Pacific Northwest, non-native fish may pose a greater conservation concern than bullfrogs, at least for amphibians.
  • Identifying pathways and vectors is critical because the easiest means to prevent and reduce the spread of new invasions is vector interception or disruption.
  • For terrestrial animals there is no comparable comprehensive list of species present throughout the Puget Sound region like there is for aquatic environments.

Residential, Commercial and Industrial Development

  • The biophysical contrasts introduced through the process of residential, commercial and industrial development – particularly through the replacement of native vegetation with impervious surfaces – impact ecological processes from the ecosystem to species level.
  • Development within the Puget Sound watershed, particularly within the central Sound region, has increased at a rate of approximately 1.4 percent per year over the last decade, and is forecasted to spread well into the Cascade foothills by 2027.
  • Canges in land cover and land use result in significant loss of nutrient and water retention, affecting water quality and quantity in the Salish Sea ecosystem. Simultaneously, such changes introduce new stressors through introduction of chemical contaminants and increased stormwater runoff.

Shoreline development

  • Approximately 99.8 percent of shoreline exhibit some level modification and degradation to nearshore processes.
  • Of the forms of shoreline modification, shoreline armoring is most prevalent, comprising 74 percent of all artificial shoreforms.
  • Shoreline modification has resulted in significant disruption or loss of important natural shoreforms such as large river deltas, coastal embayments, beaches and bluffs, and estuarine wetlands. Shorelines have also exhibited considerable shortening and simplification as a consequence of modification.
  • Dominant impacts of shoreline modification include disruption of sedimentation rates and patterns, which affect the geomorphology and maintenance of shoreform structures.
  • Ecosystemic changes resulting from shoreline modification lead to significant disruption or loss of plant and animal habitats, particularly affecting salmonids and other important aquatic species.


  • Non-point source pollution carried by stormwater and atmospheric processes represent the greatest threat of contaminant loadings from their terrestrial sources to Puget Sound.
  • Residential pollution sources are a large contributor to toxics in Puget Sound.
  • The probability of a catastrophic oil spill in Puget Sound is low but the threat of long-term damage from such an event is high.
  • A wide range of Chemicals of Concern for Puget Sound has been identified based on a broad range of conveyance pathways and contaminant types, and on the threat of harm to biota health.
  • Trophic transfer (food-web biomagnification) of persistent bioaccumulative toxics has resulted in high threat of toxicopathic disease to apex predators such as southern resident killer whales and harbor seals in Puget Sound.
  • Toxicopathic cancer in English sole from habitats along urbanized shorelines is caused by exposure to fossil-fuel compounds in their environment, and is being used to track bottom fish health through time.
  • English sole from habitats throughout Puget Sound have shown reproductive impairment related to exposure to endocrine disrupting compounds, possibly related to human wastewater.
  • Pre-spawing mortality of coho salmon returning to some urbanized stream is linked to stormwater runoff from urban landscapes.

Future Directions

We view this threat assessment as a “work in progress” and hope that other contributors will fill in missing pieces (e.g., threats to human wellbeing, and other identified threats not covered) using peer-reviewed sources, provide additional information and help identify any mistakes or misrepresentation of information.

Our review of the literature suggests that threats have been identified and classified along broad categories (Table 1). The scientific community did a good job at developing conceptual models using DPSIR framework to show linkages among threats. We tried to build on these efforts by providing information to validate those links. However, we identify the need to further demonstrate linkages and the effect of interactions among threats in a more quantitative way. We propose methods to accomplish this effort in the Introduction and Ecosytem Models sub-sections.

We also identify the need for a more comprehensive, quantitative and systematic assessment of the relative magnitude of threats and the uncertainty surrounding the relative magnitude of threats. We did not find a peer-reviewed analysis of the relative magnitude of threats for Puget Sound proper. Therefore, our Chapter treats threats separately and does evaluate the relative importance of threats on the Puget Sound ecosystem. However, we identified modeling approaches that help identify and compare threats quantitatively and the information contained in this chapter will hopefully contribute the information needed to build such models. Ideally, the models would help tease apart the confounding effects of human activities and natural events. The output of the modeling exercise would be to provide recommendation on priorities for management and policy.

More effort is needed to translate threats into measures or indicators of threats following Haines et al. 2008.

Ideally, future threats assessments would be both spatially and temporally explicit. For example, GIS maps of contamination would be comprehensive and demonstrate levels of contamination explicitly highlighting when contamination levels exceed heath thresholds or impair population survival and reproduction.



Haines, A. M., M. Leu, L. K. Svancara, J. M. Scott, and K. P. Reese. 2008. A theoretical approach to using human footprint data to assess landscape level conservation efforts. Conservation Letters 1:165-172.