On Fri, 09 Nov 2007 20:16:01 -0000, Halfordian Golfer
wrote:

On Nov 9, 8:03 am, Willi wrote:
Tim

Came across this researching something else. Thought you might be
interested:

https://research.idfg.idaho.gov/Fish...Reports/Volume...

Some different results using a different (maybe better?) methodology.
Like all fish studies, the methodology has some drawbacks but it seems
much better than the confining that the other studies used to measure
mortality in streams and rivers.

Willi

Hi WIlli,

This was a really good read, thanks for passing it along. I agree that
there are some big question marks in the technique. The results depend
on snorkelers finding the corpses of fish that die. The control being
frozen fish anchored. Seems a little questionable to me, for several
reasons, but the results being fairly consistent with the aggregate of
other studies makes me think it's a good enough methodology. Several
things are clear. 1) Mortality is cumulative, increasing fairly
dramatically as the resource is exploited 2) It was not clear in the
study if mortality during high-stress periods such as warm water
temperatures is increased, potentially exponentially 3) Mortality from
Catch and Release fishing is, and can never be, 0. Overall, this study
suggests 3% mortality from C&R through flyfishing, in Yellowstone
park. An assumption is that differing regulations, perhaps mandatory
catch/kill/quit regulations would reduce both the overall pressure,
could target desirable classes for optimal growth, yield and health of
the fishery.

Tim

o "anchor tags" does *not* mean the fish were fixed in place. It means that
type of *tags* were fixed in place - as opposed to the ribbon slips that were
simply passed through the gills. it is clear all carcasses used to refine the
methodology were allowed to "free-float".

o the temperature ranges that existed during the study periods are clearly
described, and the studies covered the warmest temperature periods recorded
for the sections of the river used.

o the methodology seems sound from here. of particular interest was the
avoidance of penning captured fish, as it removes the resulting stress from
the equation.

o if each fish caught has a 0.3% chance of dying as the direct result, and
each fish is caught 10 times during a season, the result is the 3% overall,
seasonal mortality rate. there's nothing "dramatic" about this; it is simple,
straight-line mathematics.

o no assumptions are provided in the study that changing the regulations -
short of banning all fishing - would improve the overall, seasonal mortality
rate.

o there is nothing obvious about a slot limit that would reduce the overall,
seasonal mortality rate. indeed, the opposite is *far* more likely: each fish
legally taken has a 0% probability of survival, while each fish released has
at least a 97% probability of survival...

cheers

/daytripper