Harvest rates

Chris J. Durden drdn at mail.utexas.edu
Fri Dec 17 23:26:34 EST 1999

  Here is a practice bismillenial thought. We just hit 6 billion in our
population this past fall. Look at our population growth curve now. About
time the great collector stepped in wot!
** If you are having more than one, get permission from someone who is not!**

At 03:08  17/12/99 -0500, you wrote:
>The key thing to remember here is that all mortality is not equal.  For any
>stable population, the bottom line is that each female is able to replace
>herself and a mate during her lifetime (and that pair have to successfully
>themselves).  Hence a salmon which lays 4000 eggs produces two breeding
>seven years later (if population are stable), just a a bear which produces
>one cub every two years - maybe 10 cubs total - needs to generate exactly
a pair
>by the time she dies in a stable population.
>Hence mortality of immatures in these populations has very different
>consequences.  99.99% of immature salmon are destined to die.  80% percent of
>bear cubs might suffer the same fate.  But the point that everyone
forgets, is
>that adult mortality is very different than immature mortality.  Yes, salmon
>have higher reproductive "potential" than do bears, but only in optimal
>when they do better than replace themselves.  This very basic point is why
>people justify over fishing commercial stock, and then seem surprised that by
>eliminating all the reproducing adults (literally the 2 in 4,000 that won the
>lottery and are still alive), they place population in a downward trend.  The
>argument that 99.99% of all salmon die is true from egg to adult only - yet
>applied to adults where breeding success in a stable population probably
>approaches 75%.
>In many ways, this is the invalid argument that we here over and over
again with
>regard to collecting adult insects.  To me the logic (and theoretical
>underpinnings) of the argument seem invalid at best.
>Hence in addition to "lies, damn lies and statistics", I would add  "lousy
>population ecologists" to the litany of misuse.
>Norbert.Kondla at gems3.gov.bc.ca wrote:
>> Agreed. I am cautious about all statistics.  I seem to recall a famous
>> about "lies, damn lies and statistics" :):) Maybe best to use the following
>> example with general numbers to illustrate the point that perhaps I did not
>> make very well.  A female salmon has been reported to produce between 3 and
>> 4 thousand eggs in a season.  A female bear will produce at best one or two
>> offspring every few seasons.  Given these fundamental differences in
>> fecundity; it is reasonable to expect that the impacts of mortality on
>> population levels and ability of populations to recover from crashes
will be
>> fundamentally different.  (and yes, there have been some classic management
>> errors in fisheries management - in this country we use the phrase "cod
>> scenario" to jokingly refer to harvest levels that are likely to be
>> dangerous)

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