Zy Biesinger
My research at the University of Florida focused on the habitat, movement, and performance of juvenile gag grouper (Mycteroperca microlepis) of the northeastern Gulf of Mexico.
After leaving near-shore nursery grounds during their first year, pre-reproductive juvenile gag spend two to six years moving about the shallow continental shelf before joining joining spawning aggregations at the shelf edge break. The shallow shelf landscape is characterized by flat hard-bottom (typically emergent rock covered by algae, sponge, and soft coral growth) or soft-bottom (typically sand). Gag tend to aggregate at infrequent rocky ledges or outcroppings, which are thought to serve as shelter from predators. From these central refuges, they roam across the surrounding landscape to forage.
In the balance of competing needs to shelter and forage, I asked, "What influcences how juvenile gag use the space surrounding shelter?" and "How do these space-use decisions affect individual fitness?" I focused on two potential factors: habitat and conspecific abundance.
To track the movement of unique individual gag across the landscape, we use acoustic transmitters with an array of fully sumberged, independent hydrophones. This system provides upto 5 weeks of submeter position estimates about every 6 seconds.
Experimental artificial reefs have been placed within areas representing the range of landscapes found on the shallow shelf. Because more gag tend to establish home ranges on larger reef patches (4-ball patches v. 1-ball patches), each patch represents an experimental treatment where individuals experience different conspecific abundances and different landscape compositions.
To quantify the landscape in which each reef patch is placed, using a towed side scan sonar system and making many adjacent parallel passes, we create a detailed sonar image. From this image mosaic we designate areas of sand- and hard-bottom, creating a categorical habitat map of the landscape in which individuals move. We used an Acoustic Doppler Current Profiler to continuously record detailed water flow.
Using these experimental tools it is possible to address questions about how gag movement is influenced by the landscape and conspecific abundance. Measurements of length, weight, and recent growth add the possibility of linking landscape, abundance and behavior to performance or fitness.