by Damon » Tue Nov 17, 2009 11:53 am Location: Dana 1028 (Ann Arbor)
Time: 8am
Title: Food web constraints on Chinook salmon recruitment in a large
Lake Michigan tributary.
Abstract: Food web interactions that occur over short temporal and
spatial scales may greatly affect population dynamics and management
of important fisheries. In Lake Michigan, natural reproduction of
Chinook salmon, a key target of the economically valuable sport
fishery, may vary greatly due to abiotic factors and biotic
interactions in tributary nursery areas. From 2004 to 2007, I
evaluated the relative effect of predation by stocked sport fish on
Chinook salmon recruitment in the Muskegon River, a large Lake
Michigan tributary. I conducted electrofishing surveys to estimate
growth, abundance and survival of Chinook parr, and estimated predator
densities and sampled their diets. Together, walleyes and brown trout
annually consumed from 18 to 49% of available Chinook parr. Although
brown trout consumed large quantities of Chinook parr, walleyes
consumed mainly hatchery trout. The presence of alternate prey
significantly influenced walleye predation on Chinook parr while brown
trout appeared to be limited by parr size. Walleyes positively
selected for rainbow trout in some years, and brown trout positively
selected for Chinook parr but only in April when parr were <40mm in
length. Both walleyes and brown trout selected for prey that were
smaller than the mean prey size in the environment, and prey size was
independent of predator size. I developed functional response models
to evaluate the potential for predator stocking reductions to affect
survival of Chinook parr. Brown trout had the greatest impact on
Chinook parr survival based on their feeding behavior and consumption
rates. Management efforts to reduce stocking brown trout could
increase short-term survival of Chinook parr by up to 23.4%. I used a
stage based matrix model (RAMAS), parameterized with empirically
derived estimates of Chinook survival, abundance and fecundity, to
simulate effects of predator or prey manipulation scenarios on
recruitment and population growth of Chinook salmon. In comparison to
a baseline scenario of mean predator and prey densities, only
scenarios that involved removal of brown trout significantly increased
long-term recruitment and population growth of Chinook salmon. Based
on the results of my dissertation research, I recommend elimination of
brown trout stocking in tributaries that produce Chinook salmon parr.
Damon
Or should I say Dr. baby! ha!
