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Science research shows salmon surprisingly vulnerable to things humans barely notice

Posted: June 12, 2013 - 4:55pm

The history of salmon in North America is tragic. Over and over, Euro-American settlers ate salmon, knew the fish’s value, resolved to maintain runs, and yet managed to completely destroy the stocks within a few human generations after arriving.  

We learned fairly quickly that dams destroyed fish runs and, over the long term, hatchery transplants were disastrous. We learned slowly that other things kill off salmon, too: hydraulic mining, clear-cut logging, irrigation diversions and pollution of many sorts including industrial toxins and farm run-off. The Kenai Peninsula is blessed in that it does not have those things.  

So, are our salmon safe?

Alas, no.

We are still learning — more slowly — that salmon are surprisingly vulnerable to things we do that we barely even notice.

When we put a jetty into a river, little fry can’t swim around it. When a four-wheeler turns a tiny creek into a mud wallow or the culvert on a country road erodes, the juveniles can’t get to and from summer feeding grounds. When rain slides across a greasy driveway into a ditch, it sends oily silt that kills fish eggs into the stream below. When a family clears a little “beach” on their lakefront, the water below becomes a dead zone too warm and dirty for little fish and the critters that feed them. When leaks from old septic systems work their way into creeks, the bacteria make fish sickly and the effluent fertilizes slimy weeds that coat gravel and suck oxygen out of the water. 

Some problems start far from the water. For example, contaminants gradually percolate through groundwater, flow changes can dry up creeks or pavement can transform rainwater into flash floods.

As we use computers, satellite pictures and other 21st century tools to learn more about landscapes, we are discovering that changes, often tiny by themselves, accumulate in both time and space to weaken and eventually destroy freshwater habitats and the salmon that need them. 

Every little bit of damage makes salmon more vulnerable to other stresses such as by-catch, poor ocean conditions or downturns in natural cycles.  By the time we see the habitat problems clearly, it is too late to reverse the damage.  Studies, including my own through the University of Alaska Fairbanks, show that the salmon returns are sensitive to even rural and suburban human development on the land, but often noticeable declines take decades to occur.  In other words, the consequences of our actions will not be clear until our children take our place.

Salmon evolved to bounce back from random natural catastrophes like earthquakes, floods and surging glaciers. They have an impressive record of recovery after over-fishing, including in Cook Inlet in the years after statehood.  

But they have no defense against lost habitat. Manmade efforts to restore damaged habitats, while admirable and useful, are no substitute for God’s original handiwork.

Salmon in Alaska already show signs of stress. Forecasts suggest they will have to deal with more diseases, storms, invasive species and warm water in the future.  Southcentral Alaska has gotten away with habitat abuse so far because most development only happened in the past 50 years and hasn’t had time to pass critical tipping points.

History, biology and experiences elsewhere tell us that if the people of the Kenai Peninsula pursue “business as usual” — treating habitat as our ancestors in other states did over the past several centuries — then we will lose our salmon.

Fortunately, we can do things differently.  We can learn from others’ mistakes.  We have new tools such as elevated light-penetrating walkways, bioengineered bank restoration, off-site wastewater treatment, non-toxic chemicals and open-bottomed culverts.  

But our most important tools are knowledge and motivation. Saving salmon for future generations is not painless. It involves investing money and effort, plus limiting some types of development and land use.  

The payoff goes beyond preserving salmon. If we succeed, for generations to come we will get not only nutritious, valuable and enjoyable salmon, but we also will keep a healthy landscape that provides clean water, beautiful scenery and habitat for other sensitive species such as swans and loons. We will attract visitors, support jobs and enhance property values with our renewable salmon resource. We will enjoy the privilege of living in a special place that demonstrates to the world that we can be stewards of nature’s bounty.

Shana Loshbaugh lived on the Kenai Peninsula for 20 years, mostly in Homer.  She now lives in Fairbanks, where she is a doctoral candidate in natural resource management. Her research focuses on the history of land use and salmon habitat in the Kenai River Watershed.

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