In Honor of Motherhood: Birthing in Bimini (5/10/2014)

In the photo above, taken last April, our former lab manager, Jill Brooks, inserts an acoustic transmitter into the body cavity of an adult, female lemon shark (total length--231 cm). She then took a genetic sample from this female’s dorsal fin. 

One month ago, we downloaded our receiver data near the tip of South Bimini. This same female was acoustically detected by receivers on April 10th, almost a year later, and has lingered around these past weeks since, just in time for lemon birthing season...
Is this lemon pregnant? Last year she straddled the fence of sexual maturity, ultimately proving not to be.  After a year of further development, maybe this is her big debut. Soon we shall find out. And we don’t have to recapture her or observe her birthing to know for sure.

This is because, in June of this year, the lab will perform its 20th annual PIT project, a twelve night ordeal where we use gillnets to capture, then tag and measure almost the entire population of baby and juvenile lemons in the Bimini mangrove nurseries. Recaptured juveniles from past years already have electronic PIT microtags (also called RFID tags with unique ID codes) inserted, so we can measure their growth and weight gains.  But the newborns, called neonates, will all be captured for the first time, PIT-tagged, and DNA sampled.

The above photograph shows a fin-clipping, which will soon be shipped to the states for genetic analysis. It is placed in a DMSO-filled vial to prevent DNA denaturation.

With our increasing archive of genetic material, each year we expand the family tree of Bimini’s lemon sharks to piece together a pedigree of interrelatedness. This pioneering research project can open the door for understanding the behavior and ecology of sharks down the line, paving the way for possible studies in social preference for familiars and kin. None of this, of course, could be done without the magic of the mothers, bringing a new batch of neonates to Bimini with each year. Just wanted to acknowledge the marvel at this relevant time. Happy Mother's Day!

Open Day: Bridging the Biminis through Outreach and Collaboration (4/16/2014)

A few minutes into our chitchat and introductions, I was asked somewhat off-guard, “Hey, can I take a coconut?” Looking around at the abundance of untouched green spheres hugging our palms, I mustered a nonchalant, “Yeah, for sure. ”  But with those few words, thus kicked-off a 9 person sprint-fest towards the backyard in search of the delicious snacks.

“This is the Bahaman way!” a kid known jokingly as ‘Granddaddy’ informed as he bashed his coconut into the nearest palm trunk.  And out poured the liquid.  I watched the tropical delicacy get eaten to perfection, ‘macheted,’ slurped, scooped, then shared amongst all willing consumers.  If only it was this easy when we made coconut curry the week before...

With a snack to tide our visiting students over, now it was time to focus.  The academic day began with a lecture given by one of our volunteers, Zachary Parker (right).  Over the past few months, Zach has streamlined a solid 25 minute powerpoint that we currently give for public tours.  Now a seasoned guide, he engaged the high schoolers with his knowledge and wit, spreading word that sharks are essential to this area and need be respected and understood, but not feared.  

Bryan Keller, our master’s student who initiated this outreach event, followed up Zach by giving a quick presentation on marine ecology and coastal reefs.  With head nods, questions, and input from LMHS teachers Ms. Wallis and Mr. Clark, we began a conversation about development and how dramatically North Bimini has changed since it opened its doors to tourism.

Caroline Collatos (left), here in light blue, encouraged the students to find out for themselves which fish we placed in aquariums using the Fish ID book.  She geeked out fun facts on the temporary specimens, ranging from band-tail pufferfish to sergeant majors and juvenile damsels.  And as expected, the ‘Slippery Dick’ was a class favorite, slipping it’s way into more and more conversation as the day progressed. 

The teaching trifecta then ushered the kids into our renowned shark pens, where they saw firsthand the energetic, juvenile lifeforms that depend on the same, very habitat as themselves.  Though hesitant at first to come close, by the end of the tour I believe every student worked up the courage to touch a baby shark.  Our visitors are now able to identify at least two shark species that surround the islands, those being nurse and lemon sharks.  Here, Bryan Keller holds a mellowed, juvenile lemon shark (Negaprion brevirostris) as he explains their ability to actively pump water over their gills when stationary. 

One section of the course is to show the kids how to identify a shark’s sex, here with our juvenile nurse (Ginglymostoma cirratum).  This one is a male, which can be determined by locating two claspers behind the anal fin on the shark’s underside (unshown).  

After hearing our pizza delivery would be postponed thirty minutes, we made use of the precious island time by snagging our snorkel gear and heading straight back to the seagrass.  Though most of the students didn’t have much experience with the activity nor the equipment, they seemed more than excited to cross paths with upside-down jellies, bright orange Sea Cushions, one feisty Bahaman Blue Crab, and many more little fish that poked their heads out of their cinderblock and pen mesh-made habitat.  The snorkel finaled with a series of splashes and take downs in the shallow water.

By 3 PM, the students were all changed and dried off, ready to hitch the ferry back north and call the day quits.  LMHS teachers, Ms. Lisa Wallis and Mr. Clark, appropriately sandwich this photograph, as none of this day would be possible without their support and wonderful attitudes on education.  They are incredible role models and I know Bimini’s future scholars are in great hands.  

We were sad to say goodbye to our youthful compatriots, but with exchanged emails and hugs, we know we'll do our part to ensure this tradition continues down the line. To our budding Biminites! Marine scientists in the making...

-Chris Lang, Media Manager

Hammering Home the Missing Link: Tagging & Tracking S. mokarran (4/10/2014)

This past winter, the Sharklab blazed yet another trail in the shark-tracking world. This time, by acoustically-tagging a Great Hammerhead sharks, Sphyrna mokarran. Acoustic telemetry has been used in ecology for years, yet this particular feat required a bit of ingenuity, and a fair amount of natural talent as well. 

Here lies the problem: hammerheads are sensitive. They require constant motion to flow water over their gills, a breathing process known as obligate ram ventilation. For this reason, capturing them with the typical hook-&-line method is like knocking on death’s front door, and not for ourselves. S. mokarran is an endangered and declining species, so to study these creatures with minimal impact, we would need a new solution. Our answer: pole-tagging.

With the help of The Waterman Project (www.thewatermen.org) and their founder, free-diving world-record holder William Winram (www.williamwinram.com/), we now have placed an acoustic tag beneath the dorsal fin on 17 of these enigmatic predators. First, we mounted an acoustic transmitter on the tip of a modified spear gun. Next, we tagged. Hammerheads are a particularly skittish species, so in our experience, free diving has been the most effective way to meet them underwater. William used his unique breathing superpowers to wait on the sea floor as the hammerheads approached...

Pole-tagging insertion is minimally invasive in comparison to the hooking alternative. And the prospective data we receive from these deployments may uncover so much about the otherwise uncharted life cycle of great hammerheads. For the past ten years, we have regularly spotted these charismatic predators during our winter months off the western edge of the islands. But where are they coming from, and where are they headed towards on this journey passing beside Bimini?

That’s what we’re trying to find out. For those who don’t know, Vemco is a manufacturing company that specializes in underwater tracking products used on a variety of migrating marine species. In 2006, a group of sturgeon researchers created the Acoustic Cooperative Telemetry (ACT) network. Around the same time, Sharklab founder, Dr. Gruber, and his colleagues started up an independent FACT array surrounding Florida’s coastline. What began as a small collaboration between researchers has now vasty expanded to include over 100 groups, with roughly 9500 transmitters deployed on more than 75 species. Because any Vemco receiver logs data from any passing animal equipped with a Vemco tag, the doors have been opened for cooperative data collecting. 

In January of this year, we deployed these Vemco receivers on our own turf, Bimini, Bahamas...

Around Bimini, we have installed 21 unique receivers to understand more about the great hammerheads’ relationship with the islands. We believe they migrate alongside west Bimini via the cooler Gulf Stream waters, but they have been spotted off the eastern edge in the shallow waters too, often hunting on rays (see Chapman & Gruber 1999). When a tagged hammerhead swims within 500m of any of our receivers, the acoustic signature is recorded, as well as the date and time. At the end of every four months, the Sharklab team will download the receiver data and inform us all on the hammers’ movements around the islands, both collectively and individually.

Two weeks ago, Dr. Tristan Guttridge indulged his curiosity and downloaded data from one of the 21 receivers (the one at our tagging site, located about 800m west of Shell Beach, South Bimini) as a preliminary assessment. The results were astounding. In 10 short weeks, this single receiver logged over eight thousand pings, including at least several from all 17 hammerheads we’ve tagged. Some left almost immediately after tagging, still yet to return. However, others came back repeatedly, thus proving Bimini to be more than a mere pit stop but an explorable foraging ground...though the increase in provisioning ecotourism has very likely contributed to this fidelity.

But great hammerheads aren’t the only species our receivers can track...

After downloading this data, Tristan noticed our West Grate receiver picked up two blue fin tuna (Thunnus thynnus) from Stanford’s Tuna Research and Conservation Center, tagged way up north in the Gulf of St. Lawrence, Canada. To reach Bimini they would have had to trek 2000 miles south and cross a 1000m deep Gulf Stream. Talk about some tough tuna! (Not to overlook, they were measured at 2.5m long, each).

On the very same receiver, a large tiger shark (~3.5m) from Tiger Beach, tagged by Dr. Neil Hammerschlag, spanned the Northwest Providence channel to ping us loud and clear. Apparently, all waters lead to Bimini. No wonder Ernest Hemingway found his way here.

The excitement has only begun. We have exposed a small sliver of what’s yet to discover, and time will surely work in our favor. These arrays represent so much more than a ping on a receiver. They represent a collaboration of scientists, of conservationists, of countries even, connecting data; lighting up migratory routes that have existed for eons, filling in the knowledge gaps that so often triumph over our terrestrial limitations. For this reason alone, we can celebrate a shared responsibility of ocean stewardship. Looking forward to hammering this one home. Stay posted!

We’d like to acknowledge our appreciation to the Save our Seas Foundation for making these advancements possible through their funding, helping us purchase these aforementioned receivers and temperature loggers. Participants of the Hammerhead course and research experiences have also crucially contributed to get this project off the ground. Shout outs to William Winram and The Watermen Project crew for their obvious inputs, as well as to our local dive operator, Neal Watson’s Bimini Scuba Center, for their continued generosity and supply of dive gear and tanks. 

Recapping a Recapture: Lauran's Accelerometer Deployment (4/2/2014)

One week ago, with the help of Eckerd College students, Principal Investigator Lauran Brewster tagged three juvenile lemon sharks with accelerometers in Bonefish Hole, an entranceway into one of the shark nurseries of the North Bimini Marine Reserve. These accelerometers monitor directional movements of a shark, giving us a refined look into their behavior and energetic consumption over time. Are they predominantly resting? Chasing down food? Being predated on by bigger sharks?

Each accelerometer is bound to an acoustic transmitter that pings off receivers we’ve deployed throughout the island, allowing us to track shark movement and location at the same time. As long as the battery lasts, that is. Our accelerometers measure 30 data points per second across 3 axes (x,y,z), while gauging temperature and depth every second. Such scrutiny drains the device’s battery life after five short days. So it’s no surprise that our number one task after the fact is to track down these wild sharks, retrieving our expensive equipment and the invaluable data they contain.

Before April 1st, Lauran had deployed accelerometers on 18 lemon sharks, of which 15 were successfully retrieved with usable data. I can already hear some doubters thinking: “But you just said you know their location, how hard can recapturing really be?” Certainly not as easy as it sounds. Keep reading to find out why...

On the first day of recapture, if we catch over fifty percent of the deployed sharks, we’ll call it a success. But there are the escape artists, the exploratory nomads, the ones that inevitably bypass our seine nets by the day. As a last resort, we can remove the underwater receivers in the most likely shark-traversed areas, download the data, and see if our tagged sharks made the local news. This at least gives us an idea of where to start looking. Welcome to the wonders of passive tracking.

The exact location of these sharks, however, can only be determined through active tracking. By positioning hydrophones underwater, we can pick up frequencies emitted by the shark’s acoustic transmitter. But these only have an 80 m range. The lagoon area alone spans ~ 3 x 4.5 km, and they can leave it as they please. Sounds like a needle in a haystack, or a baby shark in a really big ocean.

Fortunately, to increase our odds of success, we can rely on a bit of science. During high tide, when water levels in the lagoon rise, these juvenile sharks normally retreat into the protected mangrove nurseries. And when the tide drops, they leave their nurseries to explore and search for food. If we can intercept these juveniles at the mouth of their nursery during departure, we can hopefully find the ones equipped with accelerometers and remove them before it’s too late.

Two days ago, April 1st, 2014: With a bit of luck and tidal foresight on our side, we recaptured all three accelerometer-tagged lemons at Aya’s Spot. As the tide receded, 21 sharks vacated the channeled nursery in predictable fashion, some in sharky solitude and others in their friendly groups. It was remarkable. We tagged the sharks at high tide when they were trolling about the channel entranceway, ignorant but hopeful of their nursery preference deeper in the mangroves. It was entirely possible they had converged from different nurseries, prolonging our recapture effort, but fortunately, on this April Fool's, the joke was not on us. 

And now we can analyze the data.