Student Research Profile: Migration in white perch

Student Research Profile

Name: Brian Gallagher

Degree Sought: M.S.

Advisor: Dr. Dave Secor

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.

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?