Sea Lice and Salmon

On 16 Dec, 07:10, Tim Lysyk wrote:

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


Just a question, because I don´t know anything about pink salmon. Do
all the pink salmon of a particular year return at the same time?

Just wondering because of the two year cycle you mentioned.

Oh, and just one other point. Does this mathematical model take
population viability levels into account? Or does it just show the
time to extinction?

I saw a model here which demonstrates that population viability levels
reach a critical point quite a while before actual extinction, but
this also accelerates the extinction. ( Hope that made sense?).

Unfortunately I don´t know what this model is called.

Just a question, because I don´t know anything about pink salmon. Do
all the pink salmon of a particular year return at the same time?

Just wondering because of the two year cycle you mentioned.

All I can find is that they spawn from late-June to Mid-October, but I
don't know if that is over a wide geographic area, or if the spawning
times are more restricted on individual rivers.

Tim Lysyk

"Mike" wrote in message
...

Just a question, because I don´t know anything about pink salmon. Do
all the pink salmon of a particular year return at the same time?

Just wondering because of the two year cycle you mentioned.

Pink Salmon (also commonly called Humpies because of the pronounced hump
that forms on spawning males) - the smallest of the PNW salmon species -
mature in 2 years (1 year at sea) and, unlike many other species of salmon,
do not have some portion of the population staying at sea for longer
periods. In many watersheds significant runs occur only every other year,
with very weak runs in the off years. i.e some watersheds have even # yr.
runs while others have odd # yr. runs, and at times for no apparent reason
the cycle of the runs within a given watershed may switch from odd yrs. to
even years (or vice versa) for no apparent reason. Fish from odd yr runs
and even year runs do not interbreed, though Humpies have been known to
cross with Chum salmon producing a sterile hybrid.


Bob Weinberger La Grande, OR

Mike wrote:
Oh, and just one other point. Does this mathematical model take
population viability levels into account? Or does it just show the
time to extinction?

I saw a model here which demonstrates that population viability levels
reach a critical point quite a while before actual extinction, but
this also accelerates the extinction. ( Hope that made sense?).

Unfortunately I don´t know what this model is called.

The Ricker model is mostly used to predict a time series of data, i.e.,
numbers at one time as a function of numbers at an earlier time. It
differs from the logistic model in that negative population growth can
occur at high numbers; it becomes quite a bit more stochastic, and even
chaotic.

The authors mainly used the Ricker model to estimate population rates of
change, then used a viability analysis to estimate extinction times.

Tim Lysyk

"Bob Weinberger" wrote in message
newse49j.1098$Vg1.56@trndny04...

In re-reading what I wrote , I believe that I didn't make it clear that,
though Pinks in a given watershed are PREDOMINANTLY either odd yr or even yr
spawners, there are runs every year within a watershed.

Bob Weinberger La Grande, OR

Bob Weinberger wrote:
"Bob Weinberger" wrote in message
newse49j.1098$Vg1.56@trndny04...

In re-reading what I wrote , I believe that I didn't make it clear that,
though Pinks in a given watershed are PREDOMINANTLY either odd yr or even yr
spawners, there are runs every year within a watershed.

Bob Weinberger La Grande, OR







If you want a detailed map to see where they are talking about, here is
a link below. It is a large PDF file, about 3 megs.

http://ilmbwww.gov.bc.ca/lup/lrmp/co.../broupa62m.PDF

OK. Thanks for the info.

TL
MC