An expert in aquatic ecology told the Cohen Commission that a retrovirus is having a more devastating effect on salmon smolt as rising water temperatures put stress on them.
Dr. Scott Hinch, expert in aquatic ecology and forestry professor at the University of British Columbia took the stand as a witness accompanied by Eduardo Martins, UBC population ecologist at the Federal Judicial Inquiry in to the collapse of the 2009 Sockeye Salmon runs yesterday and today.
Hinch said the optimal average temperature for salmon is around 13-15 degrees. Over the last 20 years the Fraser River has increased by about 2 degree, often causing salmon to seek thermal refuge in cold water at the bottoms of stream or lakes.
“Survival decreases as temp increases,” said Martins, whose research showed that an increase in water temperatures would likely a higher die off rate among smolts and older salmon.
“Mortality got to be a problem at about 18 degrees in the river. When things got up to about 19 degrees stocks survived very poorly,” said Hinch.
Climate change has been showed to be a major stressor for returning salmon. But far less is known about how climate change is affecting salmon while they are at sea.
“This life stage is the most poorly understood of the salmon, there is a major data gap when they are in the open ocean,” said Hinch.
“It’s possible to keep fish alive [in warmer water temperature], if the water is pathogen free,” explained Hinch.
But the water in which B.C. salmon swim isn’t pathogen free. In fact a mysterious retro-virus that has been shown to be killing off large numbers of salmon before they have spawned. Salmon showing a certain genomic predisposition were 13.5 more likely to die before spawning than their healthier counterparts.
“Warm water highly increases the mortality rate of pre-spawning salmon,” explained Hinch. “Stress hormones impede their ability to spawn, and develop eggs and sperm. And higher temperatures, are making it harder for the fish who are experiencing disease to cope.”
Also of central concern are early entry patterns of returning salmon. Some runs are not holding in the mouth of the river as long, and are spawning as early as two months earlier that their usual run time.
Kristina Miller along with Dr. Hicks recently published a study in Science Journal that has “fairly significant findings with regards to early entry spawning”, according to lawyer Greg McDade during yesterdays cross examination. The retrovirus that has been hypothesized to be a hybrid of known strains of salmon leukemia or lymphoma, also what salmon farmers refer to as “Salmon AIDS”, has been suggested to be one of the single most important factors in the loss of salmon populations.
The Commission heard, as well, that the affects of this retrovirus may be causing early physiological development in the fish leading them to freshwater phases sooner.
As a result, sockeye returning to the Fraser River have spawned earlier than in the past.
“The core issue could be a virus reducing their ability to sustain the run of issues they experience going up the river,” said McDade.
Hinch said that the retrovirus, combined with the “variability of climate factors … could align in a perfect storm.”
Mark Worthing reports for the Martlet Newspaper at the University of Victoria and has been attending the Cohen Commission.