Thursday, February 18, 2016

Mild winter could spell disaster for salmon return

© Othmar Vohringer

According to the River Forecast Centre, the mild winter in southwestern British Columbia and on Vancouver Island resulted in extremely low snowpack in the mountains. This could cause lower water levels in the rivers. Lower water levels in the rivers mean warmer water and less oxygen. This, in turn, can have negative consequences on the returning salmon.

Low water levels and warm water makes what is for salmon an already difficult journey from the ocean upstream to the river or creek where they were born even more challenging and hazardous.

“The warmer water makes the fish weaker,” David Campbell of the River Forecast Centre has said. “It impairs their immune system, it impairs their health and it makes them far more susceptible to things like diseases.”

This means fewer salmon than forecast will make it to the spawning grounds.

In addition, according to Dr. Craig Orr of the Watershed Watch Salmon Society, above normal sea surface temperatures along the north Pacific coast could mean that salmon are likely arriving at the rivers in an already weakened state, just as they are about to embark on the most difficult and dangerous journey of their lives.

Last year British Columbia experienced a record year with the highest numbers of sockeye salmon returning to the rivers. An estimated 72 million salmon entered the Fraser River; more than double the number that returned into the river system in 2010, when 30 million salmon began their journey upstream.
My wife Heidi and I went to watch the salmon “homecoming” on a visit to the Adams River that year. It was an impressive manifestation of survival, millions of fish fighting their way to the exact spot in the river and its tributaries where they hatched a few years previously. But that was nothing compared to the images and videos I have seen from the salmon returns last year. At times there were so many fish coming upstream that one probably could have walked over them to the other side of the river without getting wet feet.

The salmon migration is one of many natural wonders that still is not fully understood. Salmon are born in rivers and streams but spend most of their adult life (two to five years, depending on the species) in the ocean. From there they migrate for thousands of kilometers back to their natal stream and the exact spot where they were born to lay their eggs and then die.

To adjust from the saltwater to freshwater and the long journey upstream fighting against strong currents, rapids and jumping up waterfalls, the fish undergoes a complete physical transformation.

Salmon returns are constantly fluctuating; there are years when we have numbers like last year, followed by years where we see fewer salmon. Fishery scientists are still trying to figure out all the details of why this is so.

While some blame mild winters and climate change, others believe that with growing populations, disease among the fish spreads faster and kills more fish. Still others think salmon returns, or their lack, has to do with rising predator numbers during good salmon years and perhaps even over-fishing.
We may never know for sure why salmon migration numbers can fluctuate so drastically from one year to the next. One thing is for certain though: when the salmon start to show up here, I will be somewhere on a river to enjoy one of the most spectacular wonders nature has designed: the annual salmon migration.

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