Oyster Reefs and the Law of Attraction

If fish could provide a review of an oyster reef, it might go something like this:

Great eats! For starters, there was a tasty and plentiful smorgasbord of barnacles, mussels, and crabs. Arrived just before high tide and the ambush action was off the chart! I’m talking all-you-can-eat baitfish and shrimp! Impressive water filtration process, too – outstanding visibility. Would rate exposure level as minimum as the structure offers a versatile make-up of pockets, humps, ledges, slits, and coves. Had a near miss with a fast-moving predator but was able to dart into a hidey hole in the nick of time. Sure, this reef is up the waterway a bit, but it is so worth the swim! My favorite go-to oyster reef! Highly recommend.

Over the past five years, Dr. Jim Morley, a fisheries ecologist, has been researching the benefits of oyster leases as a potential artificial aquatic habitat source. Dr. Morley is an Assistant Professor in the Department of Biology at East Carolina University and is located at the Coastal Studies Institute, ECU’s Outer Banks Campus.

Although there has been discussion that the installation of oyster aquaculture farms in estuarine systems poses a threat to seagrass, Dr. Morley believes the ecosystem benefits of the farms outweigh those concerns. Yielding to his inquisitive nature as a scientist, he set out to prove it.

Dr. Morley began his research with a project utilizing sonar imaging technology to compare fish abundance on leases to that on unimpacted habitat. He found fish abundances to be much greater around leases. This pattern even held up when compared to seagrass dominated landscapes.

“This is not surprising, a lot of fish like structure,” Dr. Morley said of his findings. “It was a good piece of evidence that oyster leases provide good habitat.”

However, abundance aside, there are other factors of a “good” habitat to be considered. Mortality rates, feeding opportunities, connectivity to other important habitats, and residency time must also be examined. Dr. Morley was particularly interested in residency time, the number of days that a fish is present at the site. To collect this data, fish would need to be tagged and tracked over time.

“If they [fish] are really hanging out for a long time, that suggests a quality habitat,” Dr. Morley explained.

And so, an extension of Dr. Morley’s previous work was begun with the aid of his Ph.D. student, Andrew McMains.

The first item on the agenda, is a casting call for fish that would normally thrive in natural habitats akin to what an oyster reef provides. That distinction went to the Sheepshead, with its winning school-picture-day-smile. “They associate very tightly to structure,” McMains said. Sheepshead feed on the organisms and vegetation that grow on the pilings and culture gear making up the oyster reef.

Next up, find an oyster farmer willing to allow his oyster lease to be used as a lab. Enter Jay Styron of Cedar Island Bay. Mr. Styron operates a lease about an hour away from the marine lab where McMains was working. In support of scientific research, he graciously offered his lease for study.

How does one go about tracking this odd Sheepshead fish with its set of human-like teeth? The situation calls for a little underwater intelligence via implementation of an internal acoustic telemetry tag. This gadget is a powerful tool used to gather large amounts of data that help to better understand behavior and habitat needs. In short, the tags work when sound (acoustics) is used to relay information across open space (telemetry). Unique sound pulses are heard and understood by the underwater tracking stations (receivers). External tags are not viable as they are prone to being knocked off as the fish cavort around the structure.

Between methods used in previous studies and outside help from veterinary professionals, an efficient and safe procedure was followed to surgically tag 27 fish. Once the appropriate time required for recovery was met, the fish were transported to the edge of the reef, released back into the water, and the date and time were recorded.

For this project, McMains installed a total of 17 acoustic receivers around Cedar Island Bay. Nine of these receivers were spread in an array, centered around the baskets, ropes, and other structures that make up the main oyster lease. Eight additional receivers were set up around the distant reaches of the bay. These outlying receivers reveal when fish are leaving the area, what direction they are heading, and whether they return. The use of multiple acoustic receivers and sync tags, correcting for the speed at which sound travels underwater, and implementing triangulation methods such as those used in GPS, results in highly successful fish tracking.

“That is the really cool aspect of this.” Dr. Morley stated. “Roughly every forty-five seconds, he (McMains) can see the fish’s exact location. We sort of get residency time to the extreme.”

The acoustic tags last for two months which means there will be plenty of data to analyze when the project wraps up at the end of this year.

“Oyster leases are interesting, and I think they are a good habitat, and we will hopefully be able to show that by the end of the study,” McMains said. “You know there is a reason the fish are associating to the lease here, it provides useful structure for this species. Potentially, you aren’t degrading their habitat, rather you are enhancing it by installing an oyster lease.”

Dr. Morley’s research contributes to our understanding of the effects of oyster leases on natural habitat and will influence sustainable management of resources, such as Sheepshead, in North Carolina. In the future, he plans to continue work on the impacts of oyster leases on marine life. “I would like to do a similar project with a predator, like a flounder, in an estuary where there are lots of oyster farms, to see how the predators use the broader ecosystem, in terms of leases and non-leased areas,” Dr. Morley said.

In the meantime, we’ll grab a fishing pole and check out some of the local oyster reefs.