Pre-spawn mortality in coho salmon

Pre-spawn mortality is a phenomenon where adult coho salmon, Oncorhynchus kisutch, die before spawning when returning to freshwater streams to spawn.[1][2] It is also known as Urban Runoff Mortality Syndrome in more recent studies.[3][4] This occurrence has been observed in much of the Puget Sound region of the Pacific Northwest.[5] During fall migration, salmonids (trout and salmon) pass through urban watersheds which are contaminated with stormwater runoff.[2] As the coho salmon pass through these waters, many will show symptoms of lethargy, loss of equilibrium and disorientation, and die within a few hours of showing these symptoms.[2][5] These symptoms and behaviors are prevalent after rain events.[5] Mortality often occurs before salmon have the opportunity to spawn, which is determined by cutting open female carcasses and observing for unfertilized eggs.[5] Rates of pre-spawn mortality could impact the local salmon populations.[2] Based on model projections, if rates continue, populations of coho salmon could become extinct within the next few decades.[2]

Weight of evidence suggests coho salmon pre-spawn mortality is due to exposure to stormwater runoff. A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon.[6] [7] A negative correlation exists between the incidence of pre-spawn mortality and urban land use, specifically with the impervious surfaces, commercial property type, and local roads.[1][5] Exposure to metals and petroleum hydrocarbons displayed some response to pre-spawn mortality, while exposure to pesticides, diseases, and water quality variables did not elicit this effect.[7] This trend has not been observed in any other life history stage of the coho salmon nor in other salmon species in the Puget Sound region.[1]

  1. ^ a b c Feist BE, Buhle ER, Arnold P, Davis JW, and Scholz NL. 2011. Landscape ecotoxicology of Coho salmon spawner mortality in urban streams. PLOS ONE 6(8): 1-11.
  2. ^ a b c d e Spromberg JA, and Scholz NL. 2011. Estimating the future decline of wild Coho salmon populations resulting from early spawner die-offs in urbanizing watersheds of the Pacific Northwest, USA. Integrated Environmental Assessment and Management 9999: 1-9.
  3. ^ Chow, M. I., Lundin, J. I., Mitchell, C. J., Davis, J. W., Young, G., Scholz, N. L., & McIntyre, J. K. (2019). An urban stormwater runoff mortality syndrome in juvenile coho salmon. Aquatic Toxicology, 214, 105231.
  4. ^ Peter, K. T., Tian, Z., Wu, C., Lin, P., White, S., Du, B., ... & Kolodziej, E. P. (2018). Using high-resolution mass spectrometry to identify organic contaminants linked to urban stormwater mortality syndrome in coho salmon. Environmental science & technology, 52(18), 10317-10327.
  5. ^ a b c d e McCarthy SG, Incardona JP, and Scholz NL. 2008. Coastal storms, toxic runoff, and the sustainable conservation of fish and fisheries. American Fisheries Society Symposium 64: 1-21.
  6. ^ Kolodziej, Edward (3 December 2020). "A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon". Science. 371 (6525): 185–189. doi:10.1126/science.abd6951. PMID 33273063. S2CID 227281491.
  7. ^ a b Scholz NL, Myers MS, McCarthy SG, Labenia JS, McIntyre JK, Ylitalo GM, Rhodes LD, Laetz CA, Stehr CM, French BL, McMillan B, Wilson D, Reed L, Lynch KD, Damm S, Davis JW, and Collier TK. 2011. Recurrent die-offs of adult Coho salmon returning to spawn in Puget Sound lowland urban streams. PLOS ONE 6(12): 1-12.