Posts Tagged ‘mangroves’

Tagging lemons

June 15th, 2009

Two hours after I arrive in Bimini I’m swimming with 100 sharks. This isn’t as risky as it sounds, because the sharks are less than a metre long, and they’re inside a pen in the middle of Bimini lagoon. They are lemon sharks, charcoal grey on top and white underneath, and they circle the plastic mesh walls of the pen. If I swim in the opposite direction they stream past me like cars on a freeway.

Shark census volunteer Hollie Neibert with a lemon shark she has just removed from the net.

KENNEDY WARNE
Shark census volunteer Hollie Neibert with a lemon shark she has just removed from the net.


I’m in the pen with a couple of volunteers from the Bimini Biological Field Station (aka “Sharklab”). We’re checking to see that all the sharks are healthy and swimming properly. The director of the lab, Bryan Franks, has just performed a stomach eversion on a shark caught the previous evening. After knocking out the shark with a mild anaesthetic, he gently pulled the animal’s stomach through its mouth and removed a few fragments of undigested fish from inside it. The procedure, which sounds more drastic than it actually is, took only a few minutes, and afterwards the shark resumed swimming around the pen with its fellows. Its stomach contents will be analysed as part of a study to test the long-held theory that sharks play an ecological role in culling weak and sick animals from prey populations, thereby increasing their genetic fitness.

All this activity is part of an annual census of all the lemon sharks in Bimini lagoon. Over the course of a month, nets are set each evening at strategic locations in the lagoon and monitored by volunteers throughout the night. (The work happens at night because the sharks are most active then.)

Flotilla of Sharklab boats heads into Bimini lagoon.

MATTHEW POTENSKI
Flotilla of Sharklab boats heads into Bimini lagoon.


The population study has been going for 15 years, making Bimini’s lemon sharks among the most studied sharks on earth. Researchers now have a full pedigree of the entire population (around 200 animals).

One of the current research goals is to look at the effects of nursery habitat loss on the population. Lemon sharks use mangroves as a nursery area until they reach about a metre in length and are less vulnerable to predation. On Bimini, the mangrove habitat loss is happening big-time. Resort development, channel dredging, roading and reclamation are steadily robbing the lemon shark—and other fish that use the mangrove roots as refuges—of a vital nursery ground.

A fishing guide I spoke to, “Bonefish” Ebbie, lamented the losses, saying: “Everybody chewin’ into mangroves. Sooner or later we won’t have a fishin’ village no more.”

Bimini has been called the bonefishing capital of the world. Hemingway lived here on and off in the 1930s and wrote about the experience in Islands in the Stream—the “stream” being the Gulf Stream. Bimini, the smallest of the 700 islands of the Bahamas and the closest to the US, lies on the edge of the Gulf Stream. This strategic location gives Bimini an ecological importance that exceeds its tiny size. Marine organisms spawned in its wetlands and seagrass beds may disperse for hundreds of kilometres on the aquatic conveyor belt that lies just offshore. Development threatens that process, and the Sharklab researchers want to quantify its impact.

One end of the net is tied to the mangroves, a vital nursery habitat for lemon sharks.

KENNEDY WARNE
One end of the net is tied to the mangroves, a vital nursery habitat for lemon sharks.


A couple of hours before sunset I join one of the net teams for a night of shark catching. One end of the net is tied to a mangrove trunk and the other to a pole sunk into the sediment. The lagoon is shallow, no more than about knee deep—except for soft spots where you suddenly sink to your waist. The water is 34 degrees—three shy of body heat. Every 15 minutes the net teams wade through this bath-temperature water, removing sharks or the occasional fish that gets caught in the nylon meshes. Sharks are whisked to a centrally located tagging boat for measurement and the injection of an electronic tag (which can be read with a scanner like a barcode). They are then released into the holding pen.

It’s a slow night. I’ve come to the island midway through the census, and two-thirds of the shark population has already been caught and corralled in the pen. Our team captures four sharks in the space of five hours. There’s a lot of bonhomie out here on the water. The crews are constantly on the radio, congratulating each other on a capture, ribbing each other, playing music from their iPods, posing obscure trivia questions (one of the catchers is an expert on Pirates of the Caribbean).

The two dozen volunteers come from as far afield as the UK and Holland to spend a sleep-deprived month swatting mosquitoes and being drenched by tropical rainstorms for the shark cause. I ask the crew in my boat if it’s the sharks or the camaraderie that draws them here (some come back year after year, and they pay for the privilege)? With one voice they say: “The sharks!”

Checking the net at sunset.

MATTHEW POTENSKI
Checking the net at sunset.


Around midnight everyone is thinking about the imminent food run. The radios are busy with confirmation of people’s burrito orders: One or two? Guacamole or sour cream? The skiff with the goodies is due around 12.30 am, but as the magic hour approaches so does a thunderstorm. The sky rumbles and heavy drops of rain start to fall. Before long we are all huddling under raincoats and plastic net bins as the downpour hits.

It could be worse. If the electrical activity is severe (usually heralded by the net girls’ hair standing on end with the static) crews either crawl into the mangroves and shelter under insulating plastic covers or race hell for leather back to the lab, everyone lying flat on the floor of the skiffs. You don’t mess with lightning in this part of the world.

To everyone’s relief, when the dinner boat arrives the rain eases. Sodden jackets are peeled off and the boat bilge is pumped dry. I leave the net teams to their burritos and join the boat going back to the lab. I tell them I’m feeling guilty for bailing out halfway through the session, but that I’m sure the feeling will pass. In about half an hour, as soon as my head hits the pillow.

Wild ibis chase

May 7th, 2009
Tim Laman's stunning picture of scarlet ibises in Trinidad ran in the National Geographic mangrove story in 2007.

TIM LAMAN
Tim Laman's stunning picture of scarlet ibises in Trinidad ran in the National Geographic mangrove story in 2007.

Today we searched for a bird of the mangroves, the stunning scarlet ibis. Guará, as the Brazilians call it, is one of hundreds of bird species which use mangroves as nest-building sites, overnight roosts or migration stopovers. The Parnaiba Delta is one of the areas guará has found to its liking.

We hired a speedboat at Porto dos Tatus, Parnaíba’s fishing port, and set off downstream. As we idled past floating islands of tall freshwater lilies, Ronaldo, the boatman, explained the geography of the place. The delta is like a hand, he said. The five fingers are five major rivers; the palm is a 3100 sq km labyrinth of islands and mangrove-fringed channels.

Ronaldo has lived here since childhood, and knows this wetland the way a taxi driver knows a city—with an arcane knowledge of all its shortcuts and dead ends. We sped downriver, watching as the lilies and freshwater trees and palms on the banks slowly gave way to salt-loving mangroves as the river water began to mingle with the sea. I had the sense of being among old friends: red mangroves with their characteristic looping prop roots—“the walking tree”—and black mangroves, each with an army of breathing snorkels protruding up from their underground roots.

We stopped at a fishing village where men were working with shuttles and thread in the shade of cashew trees, repairing holes in their nets. Small fish lay drying in the sun. Ronaldo found a man who knew where the ibis prefer to roost, and he joined us on the search.

At an even more remote camp, where three fishermen were resting in hammocks while their evening stew bubbled in a blackened cooking pot and a scrawny cat mewed for attention, we asked if they had seen guará recently.

“Muitos. Demais!” one replied. (“Many. Too many!”)

This sounded promising. But where would the birds be roosting today? There may have been muitos birds, but they had muitos options on where to spend the night. Compounding the problem, poachers had been operating in the delta. Ibises had become unpredictable in their roosting habits.

We tied up to a mangrove branch in a channel between two islands, ate crackers, drank water and waited for dusk, when ibises return from sea. An hour later, with a nearly full moon on the rise, Ronaldo motored around a headland and cut the engine. In the mangrove foliage dozens of egrets and cormorants flapped, jostled and screeched. As we drifted past, Elaine shouted, “I see red!” I grabbed my binoculars and there, among the snowy white of egret wings and the jet black of the cormorants, was a bird so brilliantly, totally red it looked as if it had been coloured with lipstick.

We watched for more, motoring up and drifting down as skeins of cormorants crossed the moon and circled down to land among the branches, but no more guará arrived. Yet that solitary flash of scarlet—a rose among the commoner birds—was more than worth the effort of an afternoon’s search. Indeed, seeing it on its own underscored for me the fragile importance of mangroves for a whole array of species. The indigenous Maori of my home country have a saying: Take away the flax bush, and where will the bellbird sing?

Take away the mangrove and where will the guará rest?