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> John Gilbey wrote:
>
> >I agree marine survival is a major problem, but just one of many. I repeat,
> >the fishing effort has dropped in recent years but the returns stayed down.
> >Further, have you any evidence for lower body weights in returning salmon? I
> >would be very interested in some references. I have seen no data to support
> >this view.
Debbie MacKenzie wrote:
"DFO's work includes a huge amount of research into Atlantic and Pacific
salmon, yet weight-at-age and size-at-age data I have yet to find."
Well I think your statement of a decline in avg. size at age (as well as age
at maturity) is generally correct for Pacific salmon. This data is certainly
there,
and has already been looked at quite extensively, from what memory and a
few minutes of research serves. I think one of the first people to bring it
forward
was Ricker himself (81), but it was also reviewed by Bigler et al. (96). I know
there are a lot more papers out there on the subject, but these are two of the
key
papers and were close at hand. Plus, I'm not the one looking for them ;-)
As well, Steven Hare has some interesting and very plausible (in my mind
anyway) climatic explanations for the present state of Pacific salmon stocks
and why Alaskan stocks seem to be doing well, while B.C., Oregon, Calif.,
and Wash. stocks are not.
http://www.iphc.washington.edu/Staff/hare/html/papers/inverse/abst_inv.html
Hare also has some additional information related to large climatic patterns and
Pacific zooplankton abundance. Most of which can be accessed through this link:
http://www.iphc.washington.edu/Staff/hare/html/papers/papers.html
Additionally, I find it far more likely that any negative effects due to nutrient
deficits
incurred via excessive catches of Pacific salmon would be most significant in the
natal
streams, not the marine environment. There has been a fair bit of recent
research
specifically looking at nutrient deficits (or at least reductions) in freshwater
systems
due to decreased salmon escapement. A good example with relevant references is
that
of Gresh et al. (2000).
Although I think Debbie's hypothesis has merit and probably contributes to part
of the problem, I don't think it (or the proposed solution) is the underlying
panacea to all of our problems, or all of the oceans' problems. On a bigger
picture, I can't help but see this as the temporary translocation of nutrients,
not a net loss.
The above references:
Bigler, B.S., D.W. Welch, and J.H. Helle. 1996. A review of size
trends among North pacific salmon. (Oncorhynchus spp.)
Can. J. Fish. Aquat. Sci. 53: 455-465.
Gresh, T., J. Lichatowich, and P. Schoonmaker. 2000. An estimation
of historic and current levels of salmon production in the Northeast
Pacific ecosystem: evidence of a nutrient deficit in the freshwater
systems of the Pacific Northwest. Fisheries 25(1): 15-21.
Ricker, W.E. 1981. Changes in the average size and average age
of Pacific salmon. Can. J. Fish. Aquat. Sci. 38: 1636-1656.
Hope this sheds some additional light, it certainly makes me wonder
why I am still out here in Ontario when my heart is back in B.C.!!....cue
John Denver's "Country Roads" ;-)
Alec Dale
Dept. Biol. Sci.
University of Windsor.
Windsor ON. N9B 3P4
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