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Ed Allison wrote:
> Lets say that roughly 100 million tonnes of fish are removed from the oceans
> each year. If you dried it all, it would be around 20 million tonnes.
Your back of envelope calculations are indeed stimulating and much good work
comes from envelopes rather than computers. However those calculations are
often just a good starting point. Now if most of the world's 87 million tonnes
of wild caught marine fish (FAO) come mostly from the continental shelves, then
that narrows down by quite a bit the volume of ocean where most of the fish
nitrogen is being taken from.
Actually Caddy has advance similar arguments to Debbie's if I remember them
correctly. He said it was not just top down fishing of the food web that was
contributing to fisheries crises. Nutrients were also involved. In the
Mediterranean catches were not declining because of the enclosed nature of the
basin and the high concentration of humans around it contributing nutrients.
Debbie's point is one that should be taken into account.
Actually I see the nutrient questions as an ongoing battle. In some areas,
e.g.
the deeper fisheries discussed by Merrett and Haedrich in the 1997 book,
nutrient depletions by biomass removal may well be significant factor. In
other
cases it may be one of the marginal (and ignored) factors that is eroding
marine
ecosystems. In yet other cases, the Baltic (before actions were taken to start
reversing the trend), on many coral reefs, and in the dead zone off the
mouth of
the Mississippi, there has been too much nutrient added due to human
activities.
don
Don McAllister
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