According to Canada's Globe and Mail, researchers have come to the end of a "landmark" study of Bristol Bay's sockeye salmon and have concluded that a "portfolio effect" is the main reason the area's runs have been much more stable and prolific than those in other river systems. The study will be featured on the Thursday cover of the journal Nature. The portfolio effect happens when there are multiple stocks of a particular species of salmon in one river system. During yearly river variations, conditions favor some stocks over others -- and over the long term, this means that a river's total population of fish doesn't change much from year to year even if some particular stocks may be down in any given year. The researchers argue that the effect has been key to the Bristol Bay sockeye fishery's long sustainability, as opposed to volatile runs in which the population has become homogenized -- like some hatchery-fed runs -- and thus more prone to boom-and-bust cycles. The connection between biodiversity and overall ecosystem stability has been considered established science for some time, but this is the first study that has looked at the same phenomenon within one species. So what does this mean for fisheries managers? Well, one of the researchers says it confirms what many agencies are already doing, managing for stock diversity. Read much more, here, from the Globe and Mail, and read PhysOrg.com's more technical report, here.