Last summer we started doing 52-hour active acoustic tracks with some of our sharks. This was a collaborative effort between Ashley Dawdy, an FSU Biology Honors student who examined the effects of tidal and diel cycles on bonnethead and bull shark movement in her thesis, and Bryan Keller, another PhD student working with bonnetheads in our lab. This work was intended to supplement my passive acoustic tracking and Bryan’s own research, while also making up the bulk of Ashley’s thesis (which she hopes to publish soon!), and we found it to be both very rewarding and quite challenging.
To conduct a 52-hour track we live aboard our 26-ft vessel for about three days (one day to fish and two days to track). We operate in a 3 person team (8 hours on, 4 hours off), rotating between tracking with the hydrophone and receiver, driving the boat, and attempting to sleep. We make meals in jars to avoid eating PB&J for three days straight and bring tons of water and various drinks to help keep us awake. A cot and beanbag are used for sleeping (if you can manage to get any), and we bring multiple sources of power to charge our onboard acoustic receiver. Dry bags full of spare clothes and layers to stay warm, and a big box of dry food and snacks round out our list of supplies. That is a lot of prep!
To date, we have successfully tracked 5 bonnethead sharks and 1 bull shark for 52 hours. Active tracking is some of the most rewarding fieldwork I have ever done: nothing quite feels the same as following an individual shark trying to interpret their movements, and we’re regularly treated to fantastic sunrises, sunsets, and star-lit skies. It is also extremely challenging work: the anxiety-inducing beeping of the receiver picking up the animal, threats of rough weather mid-track, and obstacles in the darkness of night (we tracked on some new moons, denying us the helpful glow of the moon) add some healthy challenge. Active tracking, though, is most of all interesting: some of our bonnetheads made unexpected forays outside the bay at night and Ashley found some significant patterns of movement rates associated with ebbing tides and periods of dawn and dusk.
We’re now analyzing data from the summer and starting to put everything together. In the next blog, I’ll begin to detail some of our results!