In this blog I’d like to touch on a shark project titled ‘Jupiter’ which is led annually by the Bimini Biological Field Station Foundation (BBFSF) team, or ‘Sharklab,' as they’re affectionately known. This project, based in Jupiter, Florida, is a 12 week annual assignment that runs between January and April.
The objective of this project is to catch mature lemon sharks (> 12-13 years of age) in a known and familiar aggregation site. Once caught, tissue samples (fin clips and blood) are taken for DNA and stable isotope analysis, along with measurements. The sharks are also internally tagged with an acoustic device. Sharks are also marked with a PIT (Passive Integrated Transponder) tag injected into the muscle next to the dorsal fin and externally tagged (National Marine Fishery Service, NMFS dart tag).
An acoustic tag is approximately as long as your index finger. It is inserted (through quick surgery) into the shark's body cavity under the muscle near the pelvic fins. An acoustic tag transmits a signal every 5 minutes and can stay active, transmitting data for up to 10 years. A large array of static receivers logging the transmitters of many sharks allows scientists to determine when the sharks form the aggregation (i.e. at specific times of day, during the summer / winter? etc) and also migratory patterns which for this particular project is crucial. A receiver is a mini-hydrophone housed in a 'techy tube' which listens for and records data from a tagged animal. The limitation with this type of tagging is marine life is only detected within a 500 meter radius of a receiver's location. This method is ideal for the Jupiter project as it allows scientists to target the aggregation with the data collected contributing towards the protection of valuable breeding sharks.
So, onto the juicy stuff! I was fortunate enough to spend a day on the boat with the BBFSF team and Captain Jo Fraser. What a day we had! The sun was shining and sea was calm and peaceful, the ideal fishing conditions! But, would we be lucky?
Task number one; like all fishing you need bait so bait cutting was the first job on the cards! Messy. The second task was setting the ‘poly ball’ lines. What are they? ‘Poly balling’ is basically just large-scale float fishing with a hook on one end and float on the surface that we can monitor from the surface. A huge benefit of this technique includes the shark's ability to swim freely, they’re not limited to a fixed location like in drum lining. This technique also reduces a shark’s hook time as it is very common for those fishing with poly balls to witness float separation/movement (you set the poly balls in a straight line so notice misalignment) and usually you’ll see a buoy/float moving through the water the moment a shark is caught. This means you catch ‘fresh’ sharks resulting in minimal anxiety and upset.
Regardless of buoy/float movement the lines are checked every hour. There’s a fine line between checking lines later and running the risk of possibly stressing a hooked shark verses checking the lines too often and disturbing/putting off any sharks interested in your bait. The Sharklab's numerous years of experience has provided the optimum timescale to check the hooks; the balance of shark safety and shark research. Finally the last task was to wait. It’s rather exciting watching the balls waiting for movement, just like rod and reel fishing you watch your float patiently and question even the slightest bob!
Within no time the first line went and it was a huge 3m+ great hammerhead! Great hammerheads are listed as Endangered on the IUCN Redlist. These Hammers are in serious trouble and with minimal scientific data for them, little can be done in protecting them at the moment.
Hammerheads are known for their sensitivity; It’s regrettably very common for great hammers to die on fishing lines or after release of big game fishing. They simply can’t handle the stress. The Sharklab, however, has a 100% success rate with 0% mortality on hammerhead captures in Jupiter, which is a rare and wonderful achievement! So, back to it; we brought the shark to the side of the boat quickly and safely to assess how she was doing. As the shark appeared somewhat stressed, no samples were taken. We noted her sex, estimated her length, and she was released immediately. It was amazing to see a team of scientists and students releasing a shark with minimal data to ensure the animal was safe. Any inclination the shark could get stressed meant the shark was released without hesitation. Shark safety was paramount. Sounds obvious? Imagine you were the scientist who required the data, would you be so quick to release the shark with the burning temptation to take samples which only take a few minutes? I was inspired and grateful to be surrounded by true shark lovers.
Fishing continued. Another line went. As always we shouted out our guesses as we all impatiently fixed our eyes on the water eager to see what we’d caught! What a sight, we all spotted the stripes as a big tiger shark cruised to the surface.
Tigers are known for being quite 'hardy' and resilient and they are one of the rare sharks that appear to be unphased (within reason) by scientists handling them. Bizarrely the tigers we caught in Jupiter were covered in some kind of slime which I hadn’t seen before. I was unsure if it was perhaps a type of defensive reaction as we were catching them so fresh? I struggled to grip them with just my hands so gloves were used for a better grip, something new to me! All details were taken this time and the shark swam off strong within 15 minutes of capture.
Next up was another hammer. This time we watched the polly ball blast through the water like a scene from JAWS! As we witnessed the ‘bite’ we had the shark secured to the boat in under 7 minutes! We placed her into tonic (i.e. upside down) and conducted a full ‘work up’. This beauty swam away strong. Such an amazing experience seeing the detail of these hammers so closely.
As we rebaited our lines we saw another ball move. This time it was another firey tiger, measuring just 210cm. This guy was full of life as sub-adult Tigers are notoriously known for having a bit of an attitude! Another full work up and off he swam.
Total sharks caught on the day: Three hammerheads ranging from 250-330 and two Tigers 210 and 260. Yep, that’s right no Lemon sharks (sad face). All data was logged and all sharks were released swimming away healthy and powerfully.
So with the sunlight fading it was time to head home. Once at the docks we off loaded our gear from the boat and cleaned every piece of equipment, down to the pencils! It’s hard to keep motivated after a tiring, yet exciting and long day in the sun but all equipment must be cleaned with fresh water as the sea salt practically destroys everything in its path with its incredibly aggressive, corrosive nature.
With all equipment cleaned and with dinner in the local diner consumed our work was done. A great day fishing and five sharks contributing towards research. In fact, since the above day took place the Sharklab's scientific data from the Jupiter sharks has gone on to protect the aggregation. An incredible result that has restricted the commercial fishing season, allowing the mature lemons to receive the protection they so rightly deserve during key mating months. How fantastic is that!!
Well another blog complete. In my next post I’ll be writing about my diving experience with notorious shark diver and world record holding freediver Mr William Winram. I can’t wait to share that with you all!
The Bimini Biological Field Station Sharklab depends on the efforts of dedicated volunteers to accomplish our research. Since its 1990 inception, the BBFS Sharklab has been host to thousands of volunteers from all over the globe. Annie Anderson blogs at Sharks Need Love.
