Drumming up Data

By Alee Knoell

Welcome, fellow NERRds, to the second installment of our Species Spotlight series, where our light today shines on Sciaenops ocellatus. S. ocellatus has many aliases: red drum, redfish, red bass, and spot-tailed bass, to name a few. Reaching five feet in length and 90 pounds, the red drum is one of Florida’s most popular gamefish and widespread estuarine fish, making appearances in freshwater, the open gulf, and coastal rivers.

Red drum are euryhaline, meaning they are able to tolerate a wide range of salinity. Additionally, they’re not too particular when it comes to temperature, which coupled with their salinity tolerance enables red drum to be such a widespread species.

This lack of pickiness also extends to the red drum diet. While as larvae they primarily eat plankton, the juvenile red drum will indulge in a wide array of eats: copepods, shrimp, marine worms, small crabs and, as they mature, other fish- very unlike the juvenile human that turns their head in horror at the sight of all things green. The adults in turn eat shrimp, blue crabs, marine worms, and fish. The primary contender of these dietary decisions does, however, vary with season, consisting mostly of fish in the winter and spring and crabs and shrimp in the fall.

Another fun tidbit about the red drum is that the individual fish’s color depends on what type of water they inhabit. Our freshwater friends take on a coloration more similar to the muddy, tannic water in which they reside and don a dark and coppery aesthetic. Alternatively, the red drums that occupy the sandy bottomed surf have a more silvery or silvery-pink look to them. Click on the gallery photos below to see which fish Aquatic Preserves manager James Tomazinis plucked from which habitat type.

The red drum also has a few tricks up its sleeve for spawning season. Aside from once again invoking this color changing phenomenon and slipping into some orange fins for the duration of the season (August- December), the males have a unique way of wooing the ladies. Using special muscles that rub against their air bladder, the male red drum produces a drumming sound (hence the name) to lure over a mate. If this bodily symphony is successful, females can produce up to two million eggs at once- enough to fill a quart and then some.

Despite its popularity and widespread reaches, plenty of details remain undiscovered about red drum.

*Cue exciting research project*

Dr. Jimmy Liao with the University of Florida Whitney Laboratory for Marine Bioscience kicked off a long term monitoring project in 2019 with the primary objective of “understanding habitat connectivity and local residence and migration patterns of breeding red drum”, as well as to learn more about how animals are moving in and out of the Intracoastal Waterway (ICW) and gauge their responses to dynamic environmental conditions, for which red drum can serve as an indicator species.

Researchers from the Liao Lab at the Whitney Laboratory for Marine Bioscience implanting transmitter in a breeding-size red drum; Photo provided by Clark Morgan

You may be wondering of all the fish in the sea, why chose red drum for this study? First, they carry a lot of local importance and value, therefore piquing the interest of scientists, charters, and local fishermen alike. There is also concern regarding the population of red drum and the pressure on them as gamefish. And finally, they serve as great indicator species because of their known migration patterns, thus helping gain insight into habitat connectivity.

OTN receivers; Photo provided by Clark Morgan

This monitoring project employs the use of passive acoustic telemetry, which Clark Morgan, the Liao lab manager and project lead, describes as a process similar to passing through a toll with a Sunpass. The system consists of transmitters and receivers (shown to the right) that communicate with each other when they come within a certain proximity. So essentially, the tagged red drum is the car and the receiver is the toll booth, but instead of a toll being payed, the event is simply documented and time-stamped. The transmitters are surgically implanted in the captured red drum. Stationary receivers are not only placed throughout the ICW, but up and down the coast from the Caribbean to Canada. This widespread installment of receivers allows for collaborative efforts between research institutes- a really cool example of the connectivity and community encouraged by scientific research. And it’s a good thing too; one of the tagged ICW fish made his merry way up to Georgia, which was discoverable through a collaborators’ receiver.

Red drum photo provided by Clark Morgan

Since this project was initiated, 39 fish have been tagged and around 7,000 events have been detected. Being a long term monitoring project, patience and time are key requirements in data collection. But the reward is evident; as their movements and migration patterns are tracked and recorded, the species profile of the red drum and the adventures they embark upon become clearer, and a steady reserve of baseline data is accumulated. Baseline data is important not only for building upon this cache of information, but also for playing a key role in being able to tell when things go south. In other words, if the species or habitat starts to display characteristics that don’t quite match up with previously collected data, it could be an indication that something is fishy (pun intended) in the system, and at the very least can stir up some inquiry.

Red drum photo provided by GTM SWMP Technician Silas Tanner

A classic paradigm of scientific research that goes hand in hand with this ‘stirring’ is that the more answers you uncover, the more questions pop up. One of a handful of questions raised by this project so far is whether dredging facilitates animal movement through the unnatural corridors it creates. Are red drum traveling from Pine Island in Ponte Vedra to the St. Johns River Jacksonville through this ‘first coast corridor’? And thus, the door is opened for potential further research, with the red drum guiding inquirers along the way. When asked if the vast difference in salinity and other water quality parameters between these two regions would be a deterrent to this excursion, Morgan replied that he is “convinced the red drum can do whatever it wants”, with which I am inclined to agree.

Click here for more information about Dr. Liao’s project. Also check out the FACT Network and the Ocean Tracking Network to further satiate any remaining curiosity.

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