On May 22, my last evening of sampling for May in Fakahatchee Bay, we caught only one shark, but that small neonate (newborn) bull shark was the one I was hoping for. I’ve been trying to acoustically tag the youngest bull sharks I can catch in the bays furthest from the altered Faka Union canal system. I’m trying to see if sharks born in bays with higher salinity patterns will seek out the altered freshwater flows coming from the Faka Union canal, where millions of gallons of fresh water are directed across the land to the Gulf of Mexico.
I’d read a paper published by Mote Marine Lab (MML) describing how the youngest, smallest bull sharks in their study were found further up the Caloosahatchee River, in the lowest salinities. They couldn’t, however, state where these sharks came from, or where they were pupped or born. I’m attempting to prove that newborn bull sharks can find the lowest salinities and will stay there to avoid being preyed upon by larger juvenile bull sharks that tend to stay in moderate to higher salinities. Let’s get back to my perfect catch that evening...
With our newborn bull shark swimming in circles in a five-foot-wide kiddie pool to stay alive and healthy, we had to first collect length data before we could perform shark surgery. One of my most enthusiastic volunteers that night asked if she could assist with the surgery. I agreed and let Kennedy Vertin, an undergraduate at USF in Tampa, hold the shark upside-down in the pool while I made a small incision in the belly area, inserted the acoustic tag, and put in three stitches to close up the opening. Meanwhile, another volunteer held a bilge pump in front of the shark’s mouth to keep water flowing into the mouth and over the gills. This technique worked well since the shark continued to swim circles in the pool after surgery.
During her recovery period, we idled the boat away from the capture gear so we wouldn’t stress the shark any further by recapturing it later that evening. Just before we released the shark back into Fakahatchee Bay, I asked Kennedy if she’d like to name our newly tagged bull shark. She replied, ‘Artemis’ and proceeded to tell us that Artemis was the goddess of the wilderness. I let Kennedy get a photo holding Artemis just before gently releasing her back into Fakahatchee Bay.
After tagging and releasing her, there’s no evidence of her movements until data from the acoustic receivers showed that the following day, May 23 at 9:30 a.m. she made an appearance in nearby Faka Union Bay. She wandered all around the bay, pinging off many of our sixteen receivers within the study area. Kennedy has the tag and receiver data for Artemis, as well as the salinity data from the area, to track the shark’s general movements and correlate with changing salinities due to tidal and canal flows. She’s using her newly acquired GIS skills to produce a pictorial view of where Artemis traveled and when.
At low tide on May 24, the receiver data showed that Artemis found the Faka Union tidal creek leading up to the dredged canal, where fresh water from the subsurface aquifer adds to the canal flow. She stayed within the canal/tidal creek for 44 days until July 7. During a falling tide, she re-entered Faka Union Bay and stayed there until the salinity reached about 22 ppt on a rising tide, and then returned to the fresher tidal creek.
For the next 18 days Artemis swam around Faka Union Bay being recorded on just about every receiver within the bay. From July 25-30, she was found in the dredged canal again. For less than one day on July 30, she swam around the bay before again returning to the canal for the next 21 days.
The story is on hold now, from late August onward, as the complete dataset has yet to be downloaded. This is hopefully just the beginning of her story, as my tags theoretically can transmit for over nine years. It’s up to Artemis to stay alive and swim by some more acoustic receivers when she can, to tell us more secrets of her survival.
Pat O'Donnell, Fish Biologist