The Nassau grouper, Epinephelus striatus, is an iconic species here in The Bahamas and throughout the Caribbean. They are the highlight of a dive in the tourism industry as well as an extremely important commercial fishery. However, they have been in decline over the last few decades and are currently considered an endangered species under the IUCN Red List1. In response, much stricter fishing regulations have been implemented (see here); Research has been increasing (see here) to learn more about their basic ecology.
One question we are investigating is what habitats sub-adult Nassau grouper use. We are wondering whether all individuals use the same habitats and space or if individuals have a preference for where to eat and how far they are willing to travel for food. For example, one grouper may prefer getting take-out from ‘Shawny’s’ where another grouper prefers ‘People’s Best Grill’ just down the block (grouper equivalents of mangrove and seagrass habitat to feed).
Juvenile Nassau grouper live in patch reef ecosystems for about 1-3 years before they migrate offshore to deeper reefs (see here for more details on their life history). In this sub-adult stage they are considered to be generalists predators, i.e., they don’t have a preference for where or what they hunt. However, recent research has shown that other ‘generalist’ predator populations are often a group of individuals with each having unique habitat and diet. A hypothesis for this individual specialization is to reduce intraspecific competition for food and space. For example, Matich et al. 2014 found that some juvenile bull sharks in the Everglades would feed upstream whereas others would migrate to feed2.
To look at the differences in habitat use of sub-adult Nassau grouper, we are using an acoustic telemetry array off the shorelines of Great Abaco. Simply, we catch grouper using hand nets or non-lethal traps (yes we have a permit), surgically insert an acoustic tag inside their stomach cavity (about the size of an Advil pill), and then release the grouper back where we found it. In addition, each grouper has a passive external tag located on its side to let fishermen and snorkelers know these grouper are a part of a study (see purple tag on grouper in photo above). Once the grouper is released, the transmitter sends off a particular signal to our receivers and they record the location of each grouper every minute (see photos below). So far, we have about half of our groupers tagged and the project is going very smoothly. I am looking forward to updating you on what we find. The project will be going on until this December.
- Cornish, A. & Eklund, A.-M. 2003. Epinephelus striatus. The IUCN Red List of Threatened Species 2003: e.T7862A12858266.
- Matich, P., M. R. Heithaus and C. A. Layman (2011). “Contrasting patterns of individual specialization and trophic coupling in two marine apex predators.” J Anim Ecol 80(1): 294-305.