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Subject: Re: "Feed the Fish"
From: John Gilbey <[log in to unmask]>
Reply-To:Scientific forum on fish and fisheries <[log in to unmask]>
Date:Thu, 9 Mar 2000 09:23:56 -0000

text/plain (98 lines)

A few more points

> 5.  The decline in the Atlantic and Pacific salmon stocks.
> John Gilbey wrote:
> >Yet in the last few years the amount caught at sea has dramatically
> >declined, BUT the stocks returning are still generally down. If only it
> were
> >as simple as a single cause for the fall in stocks, we could then do
> >something about it easily! Talking about Atlantic salmon, NASCO have
> >produced reduced quotas, NASF pay fisherman not to fish and the price of
> >salmon has fallen through the floor, added together this has meant a
> drastic
> >reduction in fishing effort and amount caught. If your arguments are
> true,
> >this should have meant the salmon stocks returning to our rivers would
> >increase, but, surprise surprise, they still continue to fall on
> many/most
> >rivers. Perhaps this means that if you base all your arguments on a
> single
> >piece of evidence or causal factor, your conclusions will be wrong. This
> is
> >school level science, in the real world there a multitude or interacting
> >factors all affecting stocks, and it these that fisheries scientists are
> >trying to understand.
> "If my arguments are true" salmon are starving at sea. Despite major
> attempts to restore and preserve river habitat and hatchery programs
> galore, salmon stocks are crashing (*only except pinks in Alaska...).
> Scientific documents I have read on salmon constantly point to "marine
> survival" as their main problem. Salmon range quite far offshore, there's
> not much to eat out there, and they don't return.
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.

> 6.  Why do I discount the importance of "El Nino" and similar
> environmental/usually "temperature" changes?
> John Gilbey wrote:
> >Again, more rubbish, if the change happen at the low end of the food
> chain
> >this will effect everything 'upstream' of this.
> >e.g. if El Nino means a drop in nutrients available to algae and plankton
> >this will limit their production, fish which feed on these will in turn
> be
> >limited, as will fish which feed on these fish etc etc. Thus the whole
> >systems biomass will fall
> Gary Sharp wrote:
> Regarding "If El Nino means a drop in nutrients available to algae and
> plankton..." - the nutrients in question being dissolved organic
> compounds:
> phosphates, nitrates, CO2? I don't see how a water temperature change of a
> couple of degrees could actually make these "unavailable" to algae. For
> some reason many elaborate analyses of the marine ecosystem have been done
> with models that seem not to really include food.
        I thought that El Nino was a reversal of ocean currents which
resulted in the nutrient rich lower water layers no longer upwelling near
the South American coast, thus no nutrients for the algae?!

> __________________________________________________________
PS, perhaps rubbish is a bit strong (bit of red mist there) but it is hard
to think of another word for some of the arguments.

> -----------------------------------------------
> John Gilbey
> FRS Marine Laboratory
> Molecular Genetics
> Victoria Road
> Aberdeen
> Scotland
> AB11 9DB
> Tel: 01224 295303
> Fax: 01224 295511
> E-mail: [log in to unmask]
> -----------------------------------------------
>  '
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