Salmon returns in the Columbia River, counted at Bonneville Dam, were the largest in 2014 than in any year since 1938, when fish counting began at the site, according to the Northwest Power and Conservation Council.
The 2014 run was about 2.5 million fish.
This is indeed good news.
But, NWPCC says these big numbers “may portend less benefit for future generations of fish” because the productivity of naturally spawning salmon is decreasing. Citing a mechanism called “density dependence,” which regulates the grown of populations, NWPCC indicates robust runs are exceeding habitat limits in some areas. These limits include the types and amounts of available food, shelter from predators and competitors, and the ability to move to other suitable habitats when needed. These limits, along with others, define the “carrying capacity” of habitat, NWPCC says. “When carrying capacity is exceeded, salmon runs can collapse quickly to levels the habitat will support.”
The Independent Scientific Advisory Board -- a panel of 11 experts that advises NWPCC, NOAA Fisheries and Columbia River Basin Indian tribes -- released a report containing detailed scientific evidence on the above. The report contains a number of recommendations for fish managers and planners, including:
-- Understanding why density dependence occurs in particular habitats and life stages of fish and accounting for density dependence when evaluating the responses of fish populations to restoration actions
-- Setting biologically based spawning escapement goals that sustain fisheries and also a resilient ecosystem
-- Balancing hatchery production and releases with the basin’s capacity to support existing natural populations
-- Improving stream habitat to help resident fish, as well as those that go to the ocean
The report, entitled Density Dependence and its Implications for Fish Management and Restoration Programs in the Columbia River Basin, is available here.
NWPCC is charged by the Northwest Power Act to develop a fish and wildlife program for the Columbia River Basin that achieves its biological objectives with minimum economic cost.