Friday, June 4, 2010

Diversity is Essential for Healthy Salmon Populations

A paper published this week in the journal Nature authored by a group of University of Washington biologists titled, "Population diversity and the portfolio effect in an exploited species" adds to large and growing body of scientific research pointing to the critical importance of lifehistory diversity within salmon populations. The group used long term data sets from the Bristol Bay Sockeye fishery, one of the worlds most productive and consistent salmon fisheries to track the relative contribution of various stocks and life histories to the fishery overtime. What they found is that while the size of some subpopulations within the Bristol Bay stock complex changed dramatically over time, the high level of diversity within the region created stability overall in the numbers of salmon returning. The new paper builds on a previous paper by the group which first described the stock portfolio effect, whereby the dynamics of a group of populations are not synchronous.

Unfortunately, Bristol Bay is exceptional in the sense that the full spectrum of the historic diversity remains intact. In many watersheds in the Lower 48 many population groups have been homogenized by a century and a half of overharvest, habitat loss and hatchery supplementation. In the Columbia system in particular where as many as 90% of the returning salmon are of hatchery origin, much of the historic diversity has been destroyed. Without high levels of diversity buffering the population from environmental variation,y the abundance of salmon booms and busts with changes in ocean productivity and river passage conditions. Work by Jon Moore at the Northwest Fisheries Science center has focused on Snake River Chinook, finding that over the last 40 years populations have become significantly more synchronous leading to large swings in productivity overall.

More information in a Seattle Times Article

Abstract of Schindler et al. in Nature

Moore et al. in Conservation Letters

1 comment:

Slint said...

Could this go a long ways in explaining the recent crash of the early kings on the kenai? Years of selective harvest have shrunk the size of the fish (killing trophies), but also must "sort" the population.