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June 23, 2021

Uncovering the Hidden Ecosystems above Oyster Reefs

When thinking about the habitat created by an oyster reef, you might picture minnows, mud crabs, and barnacles that hide in and among the shells. However, the ecosystem of an oyster reef also extends high above in the water, as larger fish also enjoy living near the structure and feeding on the smaller fish.  As part of my capstone research project comparing the health of five oyster reefs on the South River, I conducted a biodiversity assessment of these waters above the reefs. I did so using an otter trawl, which is a large cone-shaped net that is dragged behind a boat to capture any fish or other critters in the water column.

After some initial trial and error, we devised a system to smoothly deploy and retrieve the net. I surveyed the waters above oyster reefs at Duvall Creek, Glebe Bay, Persimmon Point, and a control site in the main stem of the river where there is no reef (see Google Earth image below for exact locations). I anticipated catching the most fish at Glebe Bay, which is often touted as a great spot for fishermen. To my surprise, Duvall Creek by far yielded the largest catches and the most diversity of species. The table below notes the species caught at each location.

Circled in red are the locations at which we conducted this trawl survey.
This table notes which species were found at each location.
White perch
Diamondback terrapin turtle

Some of the most exciting catches were a Summer Flounder and Weakfish, which are less common in this part of the Bay, and a Diamondback Terrapin turtle. We also caught a brown bullhead catfish and a “whale” or a blue crab measuring over 6 inches point to point. All critters were tallied, measured, and released. These data will be included in my final capstone report to serve as a resource for future oyster reef studies and restoration projects.

Many thanks to the Chesapeake Bay Foundation for lending us their trawl net and to Rich Kuhlman for volunteering his time to assist in this survey.

-Chloe Obara (Chesapeake Conservation Corps 2020-21)