Pesticides in Urban Streams and Prespawn Mortality of Pacific Coho Salmon

摘要

Pacific salmon (Oncorhynchus spp.) are anadromous, leaving freshwater as juveniles for a residency in saltwater before returning as adults to their natal stream to mature reproductively (coloration, ripening of gametes), spawn, senesce, and die (Quinn 2005). Prespawn mortality (PSM) in salmon is generally defined as adult fish that die before spawning (Wild Fish Conservancy 2008a). PSM has been documented in coho (O. kisutch, Chinook (O. tshawytscha), sockeye (O. nerka), chum (O. keta), and pink (O. gorbuscha) salmon (Quinn et al. 2007; Wild Fish Conservancy 2008a). There are multiple causes of PSM: high temperatures, low dissolved oxygen, high spawner densities, disease, parasites, and predation (Quinn et al. 2007; McCarthy et al. 2008). However, since the late 1990s, adult coho within urban streams in western Washington, with the "silver bright" and "intermediate" coloring indicative of a recent transition from seawater to freshwater, have exhibited a suite of neurological and respiratory symptoms, including disorienta-tion, lethargy, loss of equilibrium, gaping, and fin splaying. Symptoms appear soon after the fish enter freshwater with mortality usually occurring within a few hours of becoming overtly symptomatic (McCarthy et al. 2008; Scholz et al. 2011). For the purpose of the present article, we refer to this symptomatology as PSM. PSM appears to be limited primarily to adult coho of hatchery origin (Scholz et al. 2011).