Monster Seminar JAM - Anthropogenic causes of a state shift in a large river ecosystem: chinook salmon and the Snake River basin
Dr. Mark Scheuerell, Northwest Fisheries Science Center, NOAA Fisheries
Throughout the Pacific Northwest, intense efforts are underway to recover numerous stocks of Pacific salmon that are now listed under the Endangered Species Act. Much of the debate surrounding the cause of their decline centers on habitat degradation, overharvest, hydroelectric dams, hatchery production, and the introduction of exotic species. Using 40 years of data, I will show how a combination of these anthropogenic factors and poor ocean conditions contributed to a massive loss of chinook salmon from the Snake River basin. A consequent reduction in the amount of marine-derived nutrients likely caused a shift toward a much less productive state in the freshwater ecosystems that these salmon rely on for juvenile rearing habitats. As witnessed elsewhere, the survival of juvenile salmon appears positively related to the density of adult spawners during the time they rear in freshwater, suggesting a direct reliance on salmon eggs and carcasses for food. Despite relatively high numbers of adult returns in recent years following a shift toward good ocean conditions, the capacity of the freshwater environment to support juvenile salmon has decreased by more than 50%, causing an apparent negative feedback loop. Without appropriate mitigation efforts, this human-induced alternate state might preclude salmon from reaching desired restoration targets.
Date and Time:
October 21, 2004,
11:00 am - 12:30 pm