On Thursday, March 6, 2014 2:47:15 AM UTC, Russell Standish wrote: > > On Wed, Mar 05, 2014 at 05:52:20PM -0800, ghi...@gmail.com > <javascript:>wrote: > > > > > I'd always defer to an aussie on sharks...but I'm curious how they get > the > > oxygen onto their gills. Could it be they exploit currents that certain > > kinds of cave might produce? What happens when two windows are open on a > > room sort of thing? Are those cave sharks quite small, out of interest? > > Smaller fish have less oxygen demand...hence really little one don't > seem > > to need much of a sleep strategy for keeping the flow on the gills. > > The sharks in question are 2-2.5 metres in length, so they're by no means > small fish. > > But fish, in general, have lower metabolic requirements than say a > mammal of the same body mass, as they're ectothermic. > > In terms of the caves, these are open to the ocean, so with the swell, > I expect the oxygen concentration inside to be similar to that of the > open ocean. > > > > > > > > > Re dolphins, the problem is that they cannot breathe underwater, so > > > need to surface periodically to do so. Consequently, they need quite a > > > bit of brainpower (essentially to be awake) to be active all the > > > time. Fish (like sharks) do not face this problem, so can rely on > > > autonomous "breathing" via their gills. > > > > > Could be, although larger fish would feasibly have oxygen needs > > that couldn't necessarily be supplied by remaining stationary. > > Could be - I have heard the factoid that some sharks need to keep > moving. What I don't know is whether it is an urban myth or not. > If it's a myth someone should tell them they don't have to die like that when the fishermen lasso and pull 'em backward :o)
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