Spinning, Whales

Al wrote:

>The problem is the amount of plankton. Whales live in a very big
>ocean, and I strongly suspect that a couple of cubic miles of salt
>water can't possibly produce enough plankton to support one whale, much
>less a pod. Anybody have data on this?

Lovely question.

Plankton concentrations = 1 - 2.5 joules per litre.
(http://mywebpages.comcast.net/kils/biomas36.htm)

I need about 10 million joules of food a day. A 100 tonne right whale is
going to need something like 12.5 billion. Taking the high level for
plankton energy (Planks Constant!? ;-), and factoring in a magnitude
of inefficiency for a canivorous diet, the whale needs to filter-feed
something like fifty billion litres of water per day. That's a cube of
water about a third of a kilometre on an edge, per whale.

Given that Krill and much plankton require oxygen levels above those found
at 250m depth, and that plankton (all sorts of different species, remember)
reproduce over a fairly short timespan (~20 days) you might be able to
self-support a small pod of half a dozen individual great whales in an area
of 25km2, a quarter kilometre deep.

This feels more or less ok: the Southern Ocean (20 327 000 sq km - CIA
factbook) might well be able to support a population of 5 million great
whales. The calculated 95% cull in whale biomass during the 20th century,
coupled with figures for Minke whales in that region of around 300 000 make
me think this is the right order of magnitude.

That said, it would be a remarkably generous society willing to invest in
developing an environment containing a gigatonne of water per whale, in a
volume able to support half a million humans.

Andy G