Watching the river flow - the complex effect of stream variability on Bristol Bay's wildlife

Bristol Bay in southwest Alaska supports the world’s greatest wild salmon fishery.  And now scientists have a new understanding why: water temperature and stream flow.   Variation in the temperature and flow of streams is key to supporting not just Bristol Bay’s prolific salmon populations, but also the area’s immense wildlife diversity from bears to birds to plants, according to new research presented this week at the Ecological Society of America meetings in Portland, Oregon.  Working in the Wood River watershed of Southwest Alaska, scientists found that the diversity of stream conditions results in salmon that spawn at different times throughout the season, thereby extending the time that predators and scavengers can feast on this important food supply. 

As the lead author of the research explains, "Animals like coastal brown bears and Glaucus-winged gulls gorge themselves at one stream for a few weeks and then just move to another stream that might have water temperatures a few degrees warmer and therefore support salmon populations that spawn at a later time."  In this way, the diversity of stream conditions allows animals to feed on salmon over a period of three months rather than just the couple of weeks that salmon in any particular stream usually take to spawn.  

Also, add this to your list of cool things we didn’t previously know about nature:  the researchers also found that salmon play an important role in pollinating a flowering plant.  How?  Kneeling angelica, a 3-6 foot streamside plant, has evolved to bloom about a week after salmon return to a stream to spawn, at which point many of the salmon die or are consumed by bears and other critters.  Blowflies, who pollinate the flowers by swarming the blooms, then lay eggs in the decomposing carcasses of the salmon.  Those larvae emerge as adults the following year just in time to pollinate the flowers again!

This research illustrates the complexity of ecological relationships that underlie the world’s most productive salmon ecosystem.  Both the fishery’s great productivity and a diversity of wildlife are dependent on a wide range of hydrological conditions that are intricately tied to the salmon’s life cycle. That stream diversity in the area is what makes Bristol Bay’s fishery so successful and will be key to buffering the salmon and other wildlife populations that depend on them against future changes in climate conditions. 

This just shows there is even more at stake than we previously thought if a large scale copper mine is constructed and operated at the headwaters of this fishery, as proposed.  The Pebble mine in southwest Alaska poses a number of threats to salmon in the region, including the fact that copper itself can be toxic to fish and other aquatic life.  

But even if the estimated 10 billion tons of toxic mining waste stored in giant tailings ponds in a seismically active area never leaked – an experience contrary to every large scale copper mine in the world --the construction and operation of the mine alone would have a great impact on salmon populations through alteration of stream conditions. 

EPA’s recent Watershed Assessment, a scientific study of the impacts of large scale mining on the Bristol Bay watershed currently undergoing independent peer review, estimates that the mine would result in the complete loss of 55-90 miles of spawning or rearing habitat for salmon and would affect the stream flows in additional surrounding habitat by reducing stream flow and by altering the temperatures of the streams.

Thanks to the new research on stream variability we now know that these types of impacts are likely to affect not only the salmon, but  also the complex web of ecological interactions that are dependent on the specific timing of salmon populations with their natal streams that has evolved over time.  These discoveries also suggest that altering stream conditions is likely to disrupt complex relationships in ways that we do not yet even understand.

Pebble Mine could potentially devastate the ecology of the region, and is simply not a risk worth taking. It’s time to Stop Pebble Mine. Take action at

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