Student Research
Profile
Name: Brian Gallagher
Degree Sought: M.S.
Advisor: Dr. Dave Secor
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| Brian Gallagher (poorly) holding a large white perch caught this past spring. At the top of the picture, you can see Dr. Dave Secor's finger. |
For a long time,
fisheries scientists thought of migration in fish populations as more or less
uniform; that is, fish from the same population will have very similar
migration patterns, give or take a few “outliers.” This focus on dominant
trends meant that individuals who displayed unusual migratory behavior received
very little attention from researchers. In the last few decades, however, more
attention has been paid to these outliers as scientists have continually detected
the presence of two or more distinct migratory groups within many different
fish populations. This type of migratory behavior is termed “partial
migration,” and the migratory groups are (usually) called “contingents.”
My research is looking at a model species of partial
migration in fishes, fondly referred to by my advisor as the “rats of the
estuary,” the white perch (Morone
americana). A heap of previous work done in the tributaries of the
Chesapeake Bay consistently detected two contingents of white perch: one which
migrated between brackish and freshwater habitat, and one which resided in
freshwater for the entirety of its lifespan. Looking into this further,
researchers found that the prevalence of each contingent in each year class was
related to environmental conditions and that growth during the larval period
largely determined whether fish became resident or migratory. Contingents also
experienced differences in growth later in life, such that migratory fish grew
faster than their resident counterparts, but at the cost of exploiting a more
uncertain environment (think of the tortoise and the hare). Finally,
characteristics of both contingents were incorporated into an age-structured
population model, which showed that having both migratory behaviors present in
the population made it more stable over time and more resilient to perturbations.
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| Electron micrograph of a white perch otolith. At each point (white squares) an instrument measures the chemistry of the otolith, which can in turn be used to reconstruct the migratory behavior of individual fish. |
Extending from this impressive foundation, the goal of my
thesis work is to validate partial migration in white perch within the Hudson
River Estuary. The presence of partial migration in a different system would
indicate that this behavior may be a general phenomenon in white perch, and
perhaps warrants investigation in more species. Using otolith microstructure,
otolith chemistry analyses, and a long time series of environmental data, I
will be exploring potential causes and consequences of partial migration, with
the previous work done in the Chesapeake serving as a baseline. Once I get an
idea of how the environment influences migratory behavior, and how the
characteristics of the contingents differ, the final goal is to apply a similar
model as the one mentioned previously, but include projected regional warming
trends to see how the population is likely to respond to climate change in the
future.
Who would have thought those “outliers” could have such a
big impact?
