Not all the same: misconceptions on wild salmon populations
By Dave Preikshot, The Citizen July 25, 2012
I am writing to address some misconceptions that appear in the July 18, 2012 column written by Tom Paterson on the subject of salmon in B.C. I applaud his goal in writing this article but, as so often happens in complex environmental discussions, scientific evidence can be misinterpreted.
The discussion that Mr. Paterson has entered on salmon management in B.C. is an important one, and his perspective on our shared history on this topic is invaluable. However, I feel clarification is called for with respect to the science which underlies aspects of his contribution.
In the second paragraph we are told that in 2009 "...only one in 10 sockeye salmon returned to the Fraser River watershed to spawn-" This statement appears to be based on the widely reported 2009 return of adult Fraser River sockeye as one million out of 10 million expected.
The 10 million expectation was derived from a DFO pre-season abundance report (DFO 2009.
Pre-season run size forecasts for Fraser River sockeye and pink salmon in 2009. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2009/022).
In this document, the "expected" number of return migrating adults was actually reported as probabilities. The 10 million figure actually represented the point at which there was 50 per cent probability of that many, or fewer, sockeye returning. This method of reporting has become very common in fisheries management. One could think of it rather like rolling two dice. While there is about a 58 per cent chance of rolling a seven or less, there's always a chance of getting two or 12. At no point in the report is there ever the statement that 10 million sockeye were expected or certain. In 2009, then, we had the unfortunate situation of rolling snake eyes.
In fact, there was a frank admission by the authors that returning sockeye numbers could vary to a huge degree.
They state that "Forecasts are associated with relatively high uncertainty, consistent with previous Fraser sockeye forecast(s)..." Indeed the authors go on to note that numbers of returning sockeye had been at the lower end of the probability range in the recent past likely due to poor ocean survival. For example sockeye salmon "... migrated to the ocean in 2005 and returned in poor numbers (well below forecast) in 2007." Remember that in each year hundreds of millions of Fraser River sockeye smolts enter the ocean.
Historically the proportion of those surviving this ocean residency has usually been about five to 10 per cent but has ranged from about one to almost 20 per cent. This means that given our limited knowledge as to what processes in the ocean influence sockeye salmon survival we can never state that any given number will be returning. The one million sockeye that did return in 2009 probably represent something more like one per cent of the juveniles that entered the ocean in 2007. The high numbers of returning Fraser sockeye in 2010 mean that the juveniles entering the Strait of Georgia in 2008 had far higher ocean survival for reasons which remain partly unknown.
In the bulk of Mr. Paterson's article he uses the Hells Gate slide as a metaphor for the situation of 2009. This parallel seems awkward to me because the Hells Gate situation was entirely man made. Evidence provided in the reports referred to at the start of his article suggested that ocean conditions, particularly in the Strait of Georgia in 2007, likely led to poor survival of migrating juvenile sockeye salmon which were to become the returning adults of 2009. The poor oceanographic conditions facing the juvenile sockeye in 2007 were not associated with any humanderived causes. To return to the dice analogy, in 1913 we were playing with loaded dice which were going to come up snake eyes every time.
My last critique is the tendency to conflate issues facing sockeye salmon on the Fraser River with issues facing salmon populations in the rest of B.C. In the concluding paragraph Paterson states that "-our wild salmon continue to be a threatened, even endangered, species."
There are actually seven species of salmon from the genus Oncorhynchus, found on our coast; chinook, coho, chum, cutthroat trout, pink, sockeye, and steelhead. Note that brown trout and Atlantic salmon are from a separate genus: Salmo. All other trout found in B.C. belong to the genus Salvelinus.
The seven salmon species in B.C. spawn in dozens of rivers other than the Fraser and many are doing quite well. Indeed, many populations in the Fraser River are doing quite well. For more on this please see a report by Marc Labelle on south coast B.C. salmon to the Pacific Fisheries Resource Conservation Councils. In the case of Chinook, populations on the west coast of Vancouver Island and from the northern part of the Strait of Georgia appear to be doing quite well. Coho populations do appear to be relatively depressed across the province.
On the other hand, consistent and positive trends can be seen in chum and pink populations across the whole province.
Sockeye from the Fraser experienced very low ocean survivals judging by the 2009 return. This depressing figure was the culmination of almost 20 years of poor sockeye production of Fraser River sockeye. However, returning sockeye salmon num-bers in 2010 were near historic highs. Also note that one Fraser River sockeye population, the Harrison, has not shown the same declining trend in production over the last 20 years. Harrison sockeye have been returning in near historic high numbers for the last few years and 2009 was no exception. Recent scientific investigations suggest that changes in the ocean contribute as much as, if not more than, human factors to recent changes in salmon numbers across the province.
It is thus inaccurate to refer to salmon as an endangered species. Rather, they are a suite of species facing very different situations depending on local trends. What one does note is our apparent lack of knowledge as to how the ocean might influence the number of adult salmon that will ultimately return to spawn.
These salmon species not only provide economic and social benefits to our society, they also influence other species like killer whales, black bears, grizzly bears, and bald eagles among others. It is thus a duty on our part to understand why populations of salmon change so drastically, so often, and with such rapidity so that we might better act as responsible stewards of our marine and freshwater ecosystems.
Dave Preikshot Cowichan
