Theses and Dissertations


Title: THE EFFECTS OF LATITUDE ON LARGEMOUTH BASS GROWTH POTENTIAL: IMPLICATIONS OF COUNTERGRADIENT VARIATION AND POSSIBLE EFFECTS ON CURRENT BIOENERGETICS MODELS

Name: Slaughter, Joe E.

Degree: MS

Chair: Wright, Russell and DeVries, D.

Resides: SFAA

University: Auburn University

Location: Auburn

Date: 2002

Pages: 135

Keywords: largemouth bass, growth, latitude, bioenergetics

Abstract:

Largemouth bass is a widely-distributed sportfish species native to eastern North
America. Given its broad geographic distribution, largemouth bass is subject to a wide
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range of environmental conditions that, over time, may have led to the evolution of
growth differences across this latitudinal gradient. To test the potential for such latitudinal
growth differences, a two-part project was implemented.
The first component of this research was a common-garden experiment that
compared growth of age-0 largemouth bass among geographically isolated populations.
In this evaluation, adult largemouth bass from one population in Wisconsin (Micropterus
salmoides salmoides) and two populations in Alabama (M s. salmoides and M s. jloridanus) were brought to ponds in a common environment and allowed to spawn.
Their progeny were then stocked into 0.01-ha ponds and allowed to grow for
approximately one year. During the 1999 experiment, countergradient variation in the
growth of these populations was evident in that those individuals from the higher latitude
grew faster, thus exhibiting larger body size at the end of the experiment, than the
populations from lower latitudes. Largemouth bass in the 1999 comparisons were subject
to similar predator and prey densities across ponds thus representing a stable and
consistent environmental state where all populations were subjected to similar conditions.
In the 2000 pond experiments, countergradient variation was not evident and the lower
latitude population (Florida population) grew at a higher rate than either the northernmost
or southernmost populations. This difference in findings between the 1999 and 2000
experiments likely was the result of highly variable prey abundance and temperature
variations which may have lead to decreased survival and differences in largemouth bass
density. These results, although highly variable, provide evidence that, while
countergradient variation may exist among age-0 largemouth bass populations,
environmental conditions weigh heavily on bass growth and countergradient variation may
not always be evident. The second component of this study was a test of the efficacy of current
bioenergetics models to accurately predict growth given that the evolutionary past of
largemouth bass has not been incorporated into current bioenergetics models. I ran a
series of six 14-day aquarium experiments with controlled feeding rates and temperatures
that covered the range of average daily water temperature regimes experienced in central Alabama. Juvenile largemouth bass from the populations described above were used in
the experiments. Ration levels based on initial sizes for each bass were fed to each fish on
a daily basis and the total amount consumed over the 14-days was quantified. Growth was
then compared with bioenergetics model predictions based on the actual amount of food
consumed by each fish. My results indicated that survival generally was similar among
populations, decreasing as temperature increased, and that the model consistently underpredicted
growth at higher temperatures, being more accurate at lower temperatures.
Model predictions were more accurate for Florida subspecies largemouth bass than for
northern subspecies largemouth bass throughout the temperature range. Further, the
model was generally inaccurate at predicting growth for all experimental populations at all
sizes and temperatures. These results suggest that countergradient variation in first-year
growth of largemouth bass may prevent the current model from making accurate
predictions of growth. An understanding of the mechanisms by which these animals
exhibit countergradient variation is necessary for further refinement of bioenergetics model
parameters. These combined results provide managers with needed information about growth
potential of largemouth bass subspecies from different latitudes that will help in making
decisions about stocking programs. The differences in both age-0 growth potential and
the predictive ability of current bioenergetics models are ultimately influenced by
evolutionary differences among isolated populations from different latitudes. These same
evolutionary differences have led to subspecific differentiation of largemouth bass and
must be incorporated into management strategies for these subspecies. Improved understanding
of the effects of latitude on largemouth bass evolution is necessary to better
manage populations introduced outside of their native range and will provide valuable
information regarding trade-offs between conservation ethics and angler satisfaction.
Vlll

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