Re: Shark liver

Subject: Re: Shark liver
Date: Fri, 21 Jul 2006 15:35:55 +1000
> I'll take this advantage to say just how silly are the scientists
> claiming that shark liver oil per se is a deterrent to sea-birds.

The article was badly written to the point of being misleading.
The shark liver oil doesn't deter the birds per se, it deters
them from diving for baits.  (As Mike rightly points out, shark
liver is the bees knees for _attracting_ seabirds.)

Roger suggested 'Perhaps it is the "oiliness" of the shark liver
oil and not the shark odour that keeps the birds away.'  I think
that is indeed the case, and probably what the researchers were
trying to test for with vegetable oil.  I suspect the different
results is due to the different physical properties of the two
oils - shark liver oil seems to form very thin slicks over a wide
area far more readily than vegetable oil.  (I haven't found any
quantitative measurements for these oils' viscosities.) 

Simon mentioned that birds can see polarised light.  It's also
worth noting that thin films of oil can produce light interference,
e.g. "rainbows" and fringe patterns, that would be visible to
the birds.  (Rainbows are polarised, as you would discover if you
ever try to photograph one through a PL filter.)  I suspect it is
the visual appearance of the oil slick that the birds recognise and 
shy away from; the birds may not recognise the vegetable oil as
a threat until it thins sufficiently to form the interference

   Paul Taylor                           Veni, vidi, tici -
                    I came, I saw, I ticked.

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