Tag Archives: The Sea Collaborative

Happy Centennial!

Today we are set to capture and tag the 100th oceanic whitetip! We motored off, leaving the calm, aqua colored waters of the lagoon for the deep blue rolling waves of the sea. Excitement and anticipation compliment our morning coffee.

With 5 years of data coming in, the SEA Collaborative has already begun to answer important questions about the mysterious oceanic whitetip: Where do they go during the year? Do they come back? Did they get pregnant along the way? Are they having pups? How often?

It turns out that these sharks come back to the same place year after year. This especially holds true if they have round, swollen bellies: Cat Island seems to be a maternity ward for pregnant sharks!

Collecting data on a pregnant oceanic whitetip, including doing an ultrasound! Researcher Debbie Abercrombie maneuvering the shark. Photo by Andy Mann.
Collecting data on a pregnant oceanic whitetip, including doing an ultrasound! Researcher Debbie Abercrombie maneuvering the shark. Photo by Andy Mann.

But tagging sharks is not easy business.

Sometimes the hardest part isn’t their sheer size or razor sharp teeth, it’s finding them!  There were days when we just waited, waited, waited…and waited some more. The routine was the same: cut up dead fish into small chunks; tear the chunks of fish meat apart and toss them over, one at a time, into the choppy waves; scan the bright blue to the horizon for grey shadows; repeat. This part could get a bit monotonous, and, as the day went on and the hunks of fish baked in the sweltering Caribbean sun, quite stinky.  I loved every second.

Someone might take out a knife, jump overboard and “scrape” fish in the water, shredding it into the tiniest of flecks, ensuring the sea’s currents would carry the smell. Sometimes we would drag fishing lines behind the boat (called trolling), hoping to lure sharks up from the depths with promises of a freshly caught fish. Mid-day a huge sparkling yellow and blue trimmed mahi mahi snagged a line, bouncing out of the white spray of the waves, pulled feverishly by the boat. Out of nowhere, a shark emerged from the blue and snapped it in half! Within seconds, the fish and the shark were gone.

Some days, only the laughing gull following the boat would go home full, smirking and snatching hunks of fish not meant for its belly. Sometimes we saw a shark, but it wasn’t interested in our bait. Other days three oceanic whitetips would be swimming around the boat within minutes. This was not that kind of day.

We decide to take a break to fish for bait (and dinner, of course!).  Birds dive on the horizon. We are a couple hundred feet off the shelf break and reef. Lines get dropped in. Within minutes there is a bite on Joey’s line. The once-straight pole curls around towards its base, pointing at the water. Spinning feverishly on the reel, he quickly rolls it in, fighting with the fish on occasion by pulling back on the line ever so gently. The struggle is soon over. It’s a large strawberry grouper – this one’s dinner.

We head to a new location. The distant limestone cliffs of Cat Island are barley visible on the quiet horizon. The chum crate gets thrown over. It is full of fish heads, spines and tails. We began work on preparing today’s menu: frozen bonita with a side of leftover mahi heads. Today, Lucy was adding to the smorgasbord of delicacies by splashing in cups of bloody water from where the fish carcasses were kept. Sound delicious? It does it you are a shark. And that is why we are here after all.

There she was. Like magic. Our spirits rise. Appearing out of the blue as if she were next to the boat all along.

The thing is, once you see a shark, you have to hook it.  And, once you hook a shark then you have to catch it. Then the hard work starts. Including, once you collect your data, unhooking it.

A buoy gets tossed over the boat’s side. It has a line attached to it, with a hook on the other end in the shark’s mouth. She swims away freely and pulls the buoy fast through the water. This extra effort should tire her out and make her easier to tag. Quickly hopping into the small boat, passing over clunky equipment between the crests of big rolling waves, we head toward her.

Catching a shark.  Photo by Andy Mann.
Catching a shark. Photo by Andy Mann.

Tagging a shark requires being agile and deliberate. Most of all, it requires a deep respect for this animal. Jumping in and wrangling a shark will not make it sit quietly along side the boat. You need caution, experience and a lot of care.

The small boat is thoughtfully steered toward the shark: slowly maneuvering around, backing up, turning ever so slightly so the shark is facing the right direction. If she gets spooked, she will take off again. The boat follows the whim of the shark, not the other way around.

When she is secure along the side, the team hurriedly begins its work. The quicker this is done, the less stressed out the shark will be.

Measuring a shark.  Photo by Andy Mann.
Measuring a shark. Photo by Andy Mann.

The team moves about with beauty and precision, working quietly over the shark and each other. Taking exquisite care to not harm her or put themselves in danger. No nervous energy, just deliberate quick, detailed movements. Ready to pull back on a moment’s notice. Skill takes over. Read the shark, anticipate her movements, urges. Over the years, and after many scrapes and bruises, this is something the team understands. Feeling the edges of her belly tense up before she decides to flip up her tail and smack it into your side, burning the top of your thigh with her sandpaper-like skin. Or sensing her agitation and frustration before she rears up her head, swinging it around, just missing your hand.

You must trust your colleagues and trust yourself.

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Mark Bond putting an oceanic whitetip in “tonic” – a hypnotic state when they are rolled on their back. Photo by Andy Mann.

The workup usually takes less than 10 minutes.  We measure it, tag it, take a small skin sample, some blood, and do an ultrasound (yes, the same as pregnant women!), and send it on its way.

Often the sharks are in groups and its friends stick around while it is with the research team. They are usually able to catch one shark after the other, and even recapture the same sharks from one year to the next.

However, this one is alone, and she is special. Our 100th shark captured and tagged! The significance of the milestone seems to escape her as she swims hastily away, engulfed by the blue, never looking back.

Shark swimming away after getting tagged.  Photo by Andy Mann.
Oceanic whitetip under the boat. Photo by Andy Mann.
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Fishing blues

It was our first day tagging. I was nervous and excited.

Seven- to ten-foot oceanic whitetips dwarf the baby lemon sharks and bonnetheads I tagged last year. Tagging these larger, far more dangerous, animals requires a lot of skill and knowhow. Good thing the experienced SEA Collaborative (Shark Ecosystem Assessment or SEAC) researchers were running the show! Most of these scientists have been friends since graduate school and have been tagging oceanics for over five years, with many years of planning beforehand. This well-earned trust is relied upon when handling these big sharks: team members know each others’ movements; thoughts — and tagging a shark takes on the air of a well-choreographed dance.  I am learning from some of the best in the field.

Within two minutes of chumming, a ghostly grey shadow moved languidly: a broken, unsure shape glimpsed through the choppy blue surface of the water. A telltale dorsal fin broke the surface. Shark.

Delight burst through me. I jumped up to take pictures and chase the 8 ½ foot shark along the side of the boat. I took over 50 pictures in a minute.  I felt like I was 5 years old again, seeing a pile of perfectly wrapped presents on my birthday.  I thrilled with excitement, awe, wonder. But, as I looked around excitement waned and there was a quiet disappointment seeping from the team. Even from afar, they could tell this wasn’t the one we were looking for, not the infamous oceanic whitetip, just a blue shark.

Blue sharks are commonplace in the waters off New York where I am from. What was it doing all the way in the Caribbean?

As it turns out, blue sharks have the widest range of any shark species. Usually they prefer cooler water and frequent greater numbers in higher latitudes. Whitetips rule the ocean down here.

The shark was a she. On male sharks there are two short appendages that look like white asparagus stems used for mating attached their bottom (pelvic) fin called claspers. Clear evidence of mating scarred her side: a round ring of gashes in her skin made by the teeth of an amorous male blue shark no more than two weeks ago.

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Mating scars on a blue shark. Photo credit: Andy Mann.

Female sharks are actually born with thicker skin than males because they need to withstand the vicious pleasantries of mating. Males bite down hard, curl around the female and rotate her on her back, which puts her in an almost hypnotic state called tonic (a handy method we also employed when working on sharks). They then use their claspers to fertilize her.  Usually the scars heal up in about a month.

Blue sharks and oceanics are very different. But, unfortunately, they share two things in common: they are both targeted in the shark fin trade and often mistakenly killed on hooks and lines meant for other fish.

But why is the oceanic whitetip endangered, and the blue shark not?

Fundamentally the blue shark is much hardier. Many sharks die when accidentally caught on hooks of longlines set out over miles of ocean to target such fish as tuna. Called “bycatch,” this unnecessary killing happens when one species ends up dying from fishing that targets another species. Blue sharks have a much higher survival rate as bycatch when they are caught on the longline. They also reach sexual maturity around 6-8 years old, which is young compared to other sharks.  Perhaps more importantly, blue sharks have lots of babies (called pups!): around 20-50 each year compared to 2-14 for an oceanic whitetip.

Even though they make up about 40% of the shark fin trade, blue sharks are technically sustainable, teetering right on the edge of maximum sustainable yield. There are just enough blues born into the population each year to replenish the ones that die.

After a recent trip to Hong Kong, where 50% of the shark fin trade takes place, Debbie Abercrombie, one of the shark scientists, exclaimed “I can’t even believe there are still blue sharks swimming around in the ocean anymore!” She described four two-story malls filled from top to bottom dried seafood products, “…with bags upon bags of shark fins from mostly blues and some oceanics!”

Blue shark being tagged.  Photo credit: Andy Mann
Blue shark being tagged. Photo credit: Andy Mann