riverman wrote:

"Using a mathematical model of population growth rates, they show that
sea lice from industrial fish farms are reducing the numbers of wild
pink salmon - a Pacific salmon species - to the extent that the fish
could be locally extinct in eight years or less.

Dr Krkosek said the population growth rate was "severely depressed".

"It means that the probability of extinction is 100% and the only
question is how long it is going to take," he told BBC News. "

The 'probability of extinction' statement exposes that they are using
an exponential growth model, a la Malthus, while it is more likely a
logistic curve model. Logistic curves are self-correcting, although
all the mechanisms that decrease growth are not always known.

--riverman (off to create math Final exams, with his head in the
numbers)


Nope. They were using a Ricker model, modified for the two-year life
cycle of the pink salmon, which has a density dependent growth term in
it. They estimated rates of increase from an extensive data set, then
added a parasite induced mortality term estimated from years that salmon
populations were exposed to sea lice. The time to 99% extinction was
estimated from the population growth rates, and is about 4 years.

Tim Lysyk