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Déposant : Timothy Parsons
Communauté : Brentwood Bay
Déposé le : Septembre 10, 2010
Résumé :
L’ensemble des informations présentées dans le cadre de l’atelier sur le déclin des populations de saumon rouge dans le fleuve Fraser, qui s’est tenu du 15 au 17 juin 2010, ne permet pas de tirer des conclusions claires sur les causes de ce déclin. En particulier, on a omis de tenir compte de l’une des étapes du cycle de vie du saumon – le séjour en eau salée –, y compris la possibilité que tous les stocks de saumon rouge du fleuve Fraser occupent des zones presque distinctes dans le golfe d’Alaska. Cela pourrait expliquer pourquoi on observe d’importantes variations en ce qui a trait à l’importance des stocks, variations basées sur les rencontres trophodynamiques dans le golf de l’Alaska.
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Représentations :
Re: Synthesis of Evidence from a Workshop on the Decline of Fraser River Sockeye, http://www.psc.org/pubs/FraserSockeyeDeclineWorkshopLinks.pdf
Brief comment on this report by T.R.Parsons, Prof.Em. Dept.Earth.Ocean.Sci.UBC
I find the report inadequate in offering any firm conclusions on the cause of the Fraser River Sockeye decline. I recognize that the authors have attempted to balance possible causes, but none present an outstanding explanation .
The sockeye salmon spends about 70 % of its life in the ocean and yet in this report, beyond a few months in the inshore waters of British Columbia, virtually nothing is written about this stage of their life in the Gulf of Alaska. The closest the text comes to considering sockeye at sea, is in the section by Ed Farley on Bristol Bay where a study on sockeye was made in an ocean environment with the concluding statement the “carrying capacity is not unlimited, and instead is a function of ecosystem status and climate variability”. I take this to mean that the abundance and survival of salmon on the high seas is a function of their food chain and how it may vary with climate. Nowhere in the report is attention given to this kind of detail..
This raises a point about ocean survival in particular reference to different stocks of salmon on our coast. It is noted in the text that the survival of different stocks varies so that whatever happens to the Fraser Socks may not happen to Vancouver Island, or say Columbia river stocks. This is a very important question to fish feeding in the Gulf of Alaska. One gets the impression from the report that the Gulf is a big black box of more or less uniform content in which salmon just swim around and find what food they can. But the fact that different stocks appear to have different survivals indicates to me that the feeding location of different stocks may be highly specific and that it is these locations that can be very different from year to year due to a variety of oceanographic conditions which can be quite localized ( e.g. the presence or absence of a gyre ). The suggestion is not without some scientific merit – Welch and Parsons (1993) conclude from isotopic studies on salmon caught on the high seas …”that the Chilko and other sockeye stocks are geographically separated within the Gulf of Alaska..” and that … it is possible that all Fraser River sockeye stocks may occupy quasi-discrete areas in the Gulf of Alaska “ If this is true then it would go a long way in explaining (together with the work of Farley loc.cit.) why certain stocks show large variations in abundance based on their tropho-dynamic encounters in the Gulf of Alaska.
None of this is discussed in the report which relies heavily on unexplained correlations and on some observations on the early sea life of sockeye in the Strait of Georgia.
In addition to the decline of sockeye discussed in the above report, annual stock specific trophodynamic differences in ocean feeding could also account for the more recent phenomenal increase in the Fraser river sockeye returns.
Ref: Welch, D.W. and T.R.Parsons, 1993 C-13 and N-15 values as indicators of trophic position and competitive overlap for Pacific salmon (Oncorhynchus spp) Fish. Oceanogr. 2:1, 11-23.
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