Tuesday, 27 November 2018

Beyond the Tag - By Clemency White (Principal Investigator)

When you think of what shark scientists do, it usually conjures up images of tagging sharks and tracking them. Your mind immediately goes to the classic images of a team of scientists working quickly to tag and release huge sharks, it’s always a beautiful clear blue day, there are high-fives all round as the shark swims away with its new tag in tow. But how often do you consider what happens after that? How do we use the data that we get from tracking tagged animals to inform science? Welcome to Bimini...!

The Shark Lab team perform a work up on a Tiger shark (Galeocerdo cuvier) captured on a scientific longline.
© Sophie Hart / Bimini Biological Field Station
Since 1992, under the watchful eye of Dr Samuel Gruber, scientists at the Bimini Biological Field Station, “Shark Lab”, have been using data from tracking tagged sharks to answer a whole host of questions. We know that juvenile lemon sharks can swim back to their nurseries from as far away as the Gulf Stream. We know that space use is tidally linked, and juveniles will change their space use depending on whether or not predators can access the habitat they are using. We know that while adult females use Bimini to give birth, males are transient, rarely returning to Bimini after they reach sexual maturity. All of this is made possible by analysing the data obtained from tagging and tracking, particularly in long ranging marine species where physically following them by drone or boat is near impossible.

A juvenile Lemon shark (Negaprion brevirostris) swims by at one of Bimini's mangrove nursery areas, Aya's Spot.
 Sophie Hart / Bimini Biological Field Station Foundation
Over time, these datasets become even more valuable, and that’s where I come in. One of the reasons Bimini is such a special place is because of the long-term data that has been consistently collected in a standardised procedure for almost 30 years. Collating and analysing this data in one go allows us to confirm trends we have proposed from shorter studies and make new suggestions based on temporal change. While it may not be as glamorous as spending every day out on a research vessel in the Caribbean, there is a lot to be learned from spending your time running statistical models behind a screen.

During the two months I spent working on a dataset that spanned 26 years, surpassing my own age, I employed a statistical modelling technique that allowed me to see how different groupings of lemon sharks were using space. Most profoundly, I established that the space available for use by lemon sharks was reduced as a result of industrial development in Bimini. A thorough understanding of a species life history is imperative for sound conservation management techniques, and so studies like this one are instrumental in translating science to policy. This also highlights how important it is that we continue to tag and track sharks at all life stages.

So, next time you see one of those awesome pictures of sharks being tagged, consider the questions that the tag itself can answer, and how we can move forward in science and conservation - even after that shark swims far out of sight.

Tuesday, 20 November 2018

‘Turtle Day’; A visit from the FSU MTREC group - By Amanda Schadowsky

August 23rd, 2018 was the same as any morning at the Shark Lab, but for me it will forever be referred to as ‘Turtle Day’. We had visiting research assistants at the lab, from the FSU Marine Turtle Research, Ecology and Conservation (MTREC) Group, who took volunteers with them each day to assist in the field. On this particular morning a fellow volunteer and myself were selected. I was very excited because this was something new and I assumed that all the work I would be doing here was going to focus only around sharks.
After breakfast we got ready for working out in the field and grabbed the equipment we needed. We packed up the skiff and took off for the day to Bonefish Hole, a new location that I had yet to work at.
The sun was out in full effect surrounded by a picture-perfect blue sky and minimal clouds. The water was so clear, and the turquoise and blue color gradients starting from the mangrove edge was a perfect representation of the Bimini waters. I remember thinking to myself that the view was insane, and I couldn’t believe that I had the opportunity to live and work in such a beautiful place. 

As we were entering Bonefish Hole we were told to scan the water for green sea turtles (Chelonia mydas). This is where polarized sunglasses are important, so when the Shark Lab advises you to bring them, do it. The combination of the sun glare and waves makes it hard to see if you don’t. If we saw a turtle, we were instructed to point it out and the chase would begin! The turtles would try a few different tactics to get away, weaving, changing direction quickly, and sometimes completely stopping, camouflaged in the sea grass. They were quick, and we were on a small skiff, so it felt like a high-speed chase in an action movie. Once the boat was close enough, someone would shallow water dive off the front-side onto the turtle. Us volunteers were given opportunities to dive and try to catch one; unfortunately we were not as successful as the professionals! 

FSU MTREC researchers Alexa and Anthony take measurements on a green sea turtle (Chelonia mydas) during a work-up.
Sophie Hart
Once we had a few turtles in the boat, we then did work-ups on them. Measurements were taken along with small biological samples. While one turtle was getting worked-up the other turtles would make their way to the front of the boat, seeking refuge from the sun under my legs in the shade. It was truly a heart-warming moment to be near sea turtles. After the work-up was done, we were able to get photos with the turtles before releasing them. 

Turtle Day wasn’t an intense day. It wasn’t a day swimming with Bulls, Lemons, Reefs, or Tiger sharks. But, it was a day I will never forget.