Friday, July 28, 2017

Life at the Sandy Bottom


Marine scientist Anjani Ganase discusses sedimentary habitats that are abundant in the ocean but less recognized as ecosystems worth protecting.

Sedimentary habitats are exactly what they sound like, areas of sandy, or muddy marine habitats that result from settlements of sand and sediment particulates in locations of lower water movement. When we think of sandy habitats, we imagine shallow lagoonal areas along the coastline, which include areas along the bases of coral reefs in deep harbour bays such as Maracas Bay, Charlotteville and Scarborough. These types of habitats also extend to great depths beyond the continental shelf. Although these habitats may not be the postcards of marine biodiversity, the varying environments in which they are found make them quite diverse in terms of the communities that can live there. As sedimentary habitats are so extensive and rarely accessible, many of these places are underexplored especially in deeper locations; and to this today, the exploration of these habitats still results in the discovery of new species.
Flying gurnards flash their colours as they cruise over a shallow sandy bed. Photo by Anjani Ganase

What do we find?
Sedimentary habitats support marine creatures capable of living within the substrate by burrowing holes or are small enough to move between the sand particles away from predation, and include small critters, such as crabs, sea stars, clams, conch, polychaete worms and fish. Larger predators, such as stingrays, skates, sand sharks, fish and octopuses, on the other hand, forage the surfaces of these sediment beds for prey. When I used to swim laps along Grange Bay, I remember coming across clouds of sand being disturbed. As I approached the cloud, usually a stingray might be seen digging into the sand for burrowed prey. As the stingrays stir up the sediment, food is released and often a school of fish would be seen in the wake of the stingray scavenging leftovers. Even less is known about the microfauna that live in the tiny spaces between sand particles in their own microbial world, or the impacts these microbes have on the surrounding ecosystem.

Flounders are ambush predators that camouflage with the sandy substrate. Photo by Anjani Ganase

How can they live there?
The communities of organisms that live in these habitats can be very diverse. In shallow habitats, frequent disturbances such as storm debris make it difficult for permanent establishment of sessile communities because of constant shifting particulates. As a result, the residents tend to be armoured with hard outer shells or tough exoskeletons, adapted to be able to withstand being buried, and abraded by sand particles in these dynamic environments, which also act as their shields against predation. In areas of minimal water movement, poor circulation means that organisms may also have to adapt to low oxygen conditions by having smaller body size, or by living closer to the surface of sand. The feeding modes of these marine organisms also change as the environmental conditions of these sediment basins vary. In locations with constant water movement, you’ll find suspension feeders such as brittle stars and Cnidaria, while deposit feeders – crabs, urchins and molluscs – occur in calmer areas foraging the detritus that covers surfaces. In deeper locations beyond the reaches of light, the communities rely on other sources of food, such as from chemical energy at hydrothermal thermal vents or food that sinks from the surface, such as carcasses from whales and other megafauna.

What is the importance?
Much of our commercially important seafood – lobster, conch, crab, scallops and shrimp – come from sediment bottom habitats. In the Bahamas, the Queen conch and the spiny lobster are national dishes, while shrimp is popular throughout the region and globally. Apart from the consumption of this marine life, there is an attraction for recreational exploration of these habitats and the unique organisms that live there. In Southeast Asia, muck diving – diving along sediment bottoms, mostly composed of black volcanic sand – allows visitors to explore and encounter unusual marine life including the famous wonderpus octopus, a brightly banded octopus, as well as nudibranchs and disguised seahorses and frogfish and other assortment of critters. In the Caribbean, we often find flying gurnards, stingrays, and nurse sharks cruising the sandy bottoms.

However these habitats are important for other purposes. Microorganisms that live in the sediment contribute to sediment stability as they establish their homes, by making burrows or by binding sand particles together, often done by sponge species. This results in the trapping and consolidation of carbon and other materials. Organisms that remove suspended particulates from of the water column as they feed also aid in clarifying the water column. This material may include pollutants, which are then stored in the sediment, as well as in the tissues of organisms through consumption. Past studies have looked at the composition of pollutants in the tissues of organisms, such as filter feeding mussels, to determine the extent of human disturbances. Overall, the sedimentary microfauna play a significant role in the cycling of carbon, and other elements, such as nitrogen and sulphur.
Lizardfish bury themselves in the sand and wait for prey. Photo by Anjani Ganase

Threats to sediment habitats

Pollution in multiple forms is one of the biggest threats to these habitats. The dumping of garbage and old equipment may seem harmless, as people often perceive these environments as uninhabited, but these articles displace these communities. Furthermore, nutrient runoff and toxic chemicals can stifle the communities by soaking up the oxygen, especially in areas of lower circulation. These same pollutants – toxic chemicals and even micro plastics - can also build up along the food chain and impact commercially important species. Micro plastics, often ingested by marine organisms, can disrupt digestion in larger animals. Sedimentary habitats are also subject to tremendous amounts of exploitation from destructive activities such as dredging and trawling, both of which destroy these habitats by undermining the sediment structure and stability. It may be true that these habitats are less sensitive to human pollution, since, there are still important communities of organisms that utilise these spaces even when disturbed. However, considering the important roles and services that marine sedimentary habitats provide, there is need to regulate the exploitation of these environments; and to consider the effects on connected communities.
Sedimentary habitats appear to be barren at first glance but with a closer look, one will discover an array of marine life in these habitats. Photo by Anjani Ganase

References
Thompson, R.C., Olsen, Y., Mitchell, R.P., Davis, A., Rowland, S.J., John, A.W.G., McGonigle, D., Russell, A.E., Lost at Sea: Where Is All the Plastic? Science, 2004: 838.

Snelgrove, P. V. R., Getting to the Bottom of Marine Biodiversity: Sedimentary Habitats, BioScience, 1999: Vol. 49 No. 2, 129-138.

Thursday, July 20, 2017

The Travels of the Hawksbill Turtle

Marine scientist and Technical Advisor to Save Our Sea turtles (SOS) Tobago, Dr Michelle Cazabon-Mannette, describes the fascinating life cycle of hawksbill turtles, the long journeys they make, the different habitats they inhabit, and the challenges they face. This article first appeared in the Tobago Newsday on Thursday 20h July 2017

A hawksbill hatchling makes its way to the sea. Photo courtesy Ryan P. Mannette

We start the tale on a warm sandy beach in the tropics, where a female hawksbill has laid a clutch of about 150 round white eggs each the size of a golf ball. The eggs will incubate for about 60 days, before hatching in synchrony. Once the eggs hatch, it takes several days for the hatchlings, with an average shell length of just 4cm or 1.5 inches, to climb to the surface of the sand. They work together to wriggle their way through the sand, but once they hit the surface, it’s “every man for himself” as they make a mad dash for the sea. Natural instincts kick in and the hatchlings head for the brightest source of light (the sea) and then from the water’s edge they head into the oncoming waves. It is at this stage that they are most vulnerable to their natural predators which include various species of birds, mammals and even crabs and ants. Those hatchlings that survive their treacherous trip across the beach face more predators waiting for them just offshore, including birds and several species of fish. Many young turtles will be lost as they run this gauntlet of predators, but this loss is compensated for by the high numbers of eggs that each female turtle can produce in her lifetime - laying on average 4-5 clutches of 140-158 eggs each, every 2-4 years, over a period of several decades.

The hatchlings continue to swim away from shore, and go on to spend their first few years of life in the surface waters, out in the open ocean. This period of their life is often referred to as the “lost years” since they are so difficult to study at this small size and so little is known about where they go. Their route across the ocean basin is determined by a combination of the ocean currents, and their swimming behaviour. They can travel for hundreds to thousands of kilometres during this time, and are often found in association with masses of seaweed such as Sargassum, where they shelter from predators and feed. Unfortunately plastics and other pollutants that drift at the surface can also accumulate in the same areas, which make these young turtles prone to accidentally ingesting them.

Only when their shell is about 20-35cm (8-14 inches), a few years after leaving the nesting beach, do we begin to see juvenile hawksbill turtles close to shore feeding at coral reef, hard bottom and cliff-wall habitats. This represents a major change in their lifestyle, from drifting far from shore and feeding near the surface, to living close to shore and feeding almost exclusively on sponge (simple invertebrate organisms that grow fixed in one place) at the seafloor. This is quite a unique diet – few other animals feed on sponge in such great quantities. As a result of their dispersal at sea, hawksbills at any feeding ground would have originated from several different distant beaches. Once juvenile hawksbills make this shift to a nearshore habitat, they have already travelled great distances. But, their travelling ways change for the time-being – they remain within a relatively small home range for several years, until they approach maturity at the age of about 25-35 years. During this period, these juvenile turtles can still be prone to large natural predators like sharks as they spend their days foraging for food, and their nights resting on the reef.

Juvenile hawksbill foraging on a reef. Photo courtesy Ryan P. Mannette

On approaching maturity, at about 70cm shell length (28 inches), hawksbills migrate to an adult foraging ground, which may be closer to the nesting population to which they belong, but resembles the same type of habitat where they would have spent their juvenile years while developing, therefore there is no major change in diet or lifestyle. From there, females set out on their breeding migrations every 2-4 years on average. Each female returns to the beach where she was born, in an amazing feat of navigation, over distances as much as hundreds or even thousands of kilometres, to mate and lay her own eggs on, or very close to, the very same beach she left as a hatchling about 30 years before. Less is known about adult males, but it is believed that they make shorter breeding migrations every year, to nearby nesting beaches that are not necessarily their beach of origin. Adults continue making these migrations for at least 2-3 decades. And so the circle of life continues as each new generation of ocean ambassadors is deposited in the warm tropical sand, waiting to begin their journey.

 

Saturday, July 15, 2017

Hold your breath and dive deep!

Spearfisher Phillip Almandoz gives his insight to the sport of spearfishing and discusses the progress of the Tobago Freedive Spearfishing Challenge which he started in 2010. This year, 2017, it was held on June 17 and 18; and hosted in Castara, attracting a large number of freedivers in their search for underwater game.

Free-spirited freediving spearfishers celebrate after this year's rournament. (All photos courtesy Phillip Almandoz)


The challenge is to dive, spear a fish and return with it to the boat, on one breath. Some people can dive deeper than 100 feet on one breath. My normal dive on a single breath is 1.15 to 1.30 minute. I don’t try to push myself; after all, I have a young family, my wife and two children, six and three.

Freediving is a very dangerous sport. You should be trained. And you have to be very disciplined. Just think about it, you dive deep, spear a fish and have to fight to get the fish back to the surface. If you overspend your time down there, it’s possible to black out on the way up.

We don’t know what might have happened with Sunil Boodram – who was a keen participant in the Challenge for the past few years – but it must have been something unusual for him to drown in 20 feet of water, at Little Englishman’s Bay. He was one of the most enthusiastic free divers, improving after he did the Free Dive Course. He was also a good spear fisher. He brought up one of the biggest kingfish I’ve ever seen on a spear. He was an eager and competent diver.

All I can say is, don’t dive if you aren’t feeling well, if you aren’t in top form. What happened to Sunil is very sad; and my sympathy is with his family.
Phillip Almandoz presents a prize to Sunil Boodram in the 2017 Tobago Freedive Spearfishing Challenge

Sunil Boodram with his horse eye cavalli
THE CHALLENGE
In 2010, I started the Freedive Spearfishing Challenge in Tobago, to bring together free diving spear fishermen from all over Tobago and Trinidad. There aren’t that many of us. There are plenty scuba divers, and many scuba divers who spear fish. In 2010, there were 24 competitors. Last year, 2016, we had 42 divers. This year, we were 34 divers including one woman.

The rules are based on an international point system. I get some sponsorship from suppliers, and the sale of the fish we catch goes to offset the rest of the cost.

The categories of the Challenge include the point system; Heaviest Fish; and a Junior Category. This year, we added the Lionfish Category and a video competition. Divers attach GoPro cameras to their spear guns or their heads; the footage is always exciting; with good editing, you have fantastic videos.

In all categories, you get one point per pound of fish and one additional point per fish. Maximum per fish is 21 points; three fish per allowed species. Your targets are certain types of fish, with weight restrictions for each type: briefly, no small fish, no billfish, no parrotfish, no goliath groupers. The Lionfish category was introduced to remove this invasive species from our reefs. I’m glad to report they are now being caught in fish pots. Once you know how to clean them, lionfish is one of the most delicious fish.

You are allowed to dive and fish anywhere around Tobago. Before you dive, the boat is inspected; and there are inspectors available in Scarborough, Pigeon Point, Charlotteville and Castara. Weighing takes place at Castara in the evening; you can bring the fish back by boat or by road, but all fish must be kept on ice.

This was a very good year; we weighed over 1000 pounds of fish. We sell the fish to cover costs; and the balance goes to charity, a home for the elderly.

Castara is the host for the Challenge because we were treated well there from the beginning. We choose two days on a long weekend, so that the occasion attracts people who also come to support the divers. The weekend has to coincide with the moon in the first or last quarter when the sea is calm with the slackest current.

So yes, it is a festive weekend in Castara, and the village benefits from an influx of business for a couple days.

Our top fishermen this year were Josh Lewis and Brett Thompson, both from Trinidad. Richard Parkinson from Tobago is usually in the top three. (See who topped the Challenge in all categories attached.)


ADVICE TO NEW FREE DIVERS
Take the free diving course; this is available in Trinidad as well as Tobago. I started spearfishing as a kid, went away to school and got back into it in 2005: that’s over 25 years! Now, I usually get in a good dive once a month. If I go out on a boat, it's to St Giles, Speyside, the rigs in Scarborough, anywhere around Tobago. I did shoot my biggest fish on a near shore dive, in Little Englishman’s Bay, a 60-lb cobia. I dive in my comfort zone, I’m not trying to set any records so I don’t push myself. Men like Josh Lewis and Brett Thompson may go beyond 100 feet deep and spend two minutes underwater. To do that, you must be physically fit. You must be disciplined. (Pat Ganase)


2017 TOBAGO FREE DIVE SPEARFISHING CONTEST RESULTS

WINNERS BY WEIGHT
Edmund Alley: 49.55lb barracuda
Lehron Brooks: 45.1 lb Cubera snapper
Josh Lewis: 31.95lb barracuda
Dillon Ragoonath: 29.8lb pompano
Brett Thompson: 27.95lb horse eye cavalli
Maurice Aboud: 27lb barracuda
Tony Chameley: 26.3lb barracuda
Richard Parkinson: 24.75lb barracuda
Marc Jaikeran: 20.8lb pompano
Allon Williams: 20lb horse eye cavalli

MOST POINTS
Josh Lewis, 407.45
Brett Thompson, 377.35
Richard Parkinson, 263.8

JUNIOR CHAMPION
Anthony James

FEMALE CHAMPION
Danielle Bachew

VIDEOS
Richard Parkinson
Edmund Alley
Stephan Berkley
Josh Lewis
Aldo Abraham
Lehron Brooks with one of the heaviest fish in the tournament, a Cubera snapper

Maurice Aboud, barracuda

Edmund alley, barracuda, heaviest fish caught

Phillip Almandoz presents prize for most points to Josh Lewis

Danielle Bachew, lone woman


Anthony Graham, largest lionfish

Anthony James, junior champion,

Josh Lewis, crevalli jack

Richard Parkinson, yellow jack

Dillon Ragoonath, pompano

Brett Thompson, mutton snapper

Brett Thompson, horse eye cavalli

Friday, July 7, 2017

Why we should stop eating sea turtles

Marine scientist, Dr Michelle Cazabon-Mannette, argues that turtles alive are far more valuable than for food.
This loggerhead turtle was recently stranded on the east coast of Trinidad with a possible boat strike injury. "Sammy" is currently undergoing treatment (Ryan P. Mannette)

 In Tobago we have a taste for turtle meat, and many of us think it is a luxury that is our right to enjoy. But it is a luxury that right now we have to learn to forego. Why?
1)    Sea turtles are valuable in many ways, and we want future generations to be able to enjoy and benefit from these values.
Sea turtle products such as meat, eggs and shells have been consumed by man for thousands of years. Prehistoric peoples in the Caribbean exploited sea turtles substantially, for at least 4,000 years. There is no denying these animals are a valuable source of protein. We say sea turtles have consumptive value because their products can be consumed.
Sea turtles can also be considered valuable in terms of recreation or tourism. Like many species of wildlife, some people enjoy having close interactions with them in the wild, and pay to do so. This is most apparent with sea turtle nesting tours – for example, in 2014, 14,291 visitors were recorded at Matura beach, and tour fees totalled TT$290,276. Turtles are also encountered by divers and snorkellers, and such encounters add value to the activity. Divers are willing to pay considerably more for SCUBA dives if they will encounter sea turtles.
Arguably the greatest value of sea turtles that goes largely unnoticed, is the critical role they play in contributing to a healthy marine ecosystem. Through their diet, sea turtles contribute to healthy coral reefs, seagrass beds and fisheries.

2)    Sea turtle populations are very sensitive to harvesting and can decline very quickly as we have seen in the past.
Sea turtles are particularly sensitive because of their biology. They take decades to reach sexual maturity, and only approximately 1 in 1000 eggs will survive to adulthood, as a result of natural predators that prey mainly on their young. Those that do reach maturity have few natural predators and are able to survive and reproduce over several more decades. This system is quite successful for sea turtles (which have been around for about 100 million years), when there is no additional threat from man. But even small losses from the population due to harvesting can be devastating.
After European colonization of the Caribbean, sea turtles were quickly over-exploited in commercial fisheries and their populations dramatically declined within just 200-300 years (4-6 sea turtle generations). For example a large nesting population in Bermuda was completely exterminated by 1800. It is important to note that this occurred before industrialization, when the human population was still quite small, and before motorized ships, the industrial fishing gear we have now, and other contemporary threats like plastics.

3)    Sea turtle populations are now considered globally endangered and face many significant threats besides harvesting.
Sea turtles are considered globally endangered because their numbers have declined quickly within just a few generations. Some individual populations may be quite large and doing relatively well, like our local leatherback population, but we must consider how other populations are doing around the world too. 
Some of the other threats they face include plastic pollution, fisheries bycatch and entanglement in discarded fishing nets and lines, climate change, artificial lights, loss of nesting beaches, degraded feeding habitat offshore and boat strikes.
Conservation is about managing the use of natural resources (like sea turtles, fish, coral reefs, seagrass beds, water, forests etc), in order to ensure that we maximize the values or benefits we get from them for as many people as possible, and for future generations. If we apply this to a species like sea turtles, this means taking steps to ensure there are enough individuals to allow for use in the variety of ways listed above, now and into the future. For a species that is harvested, steps to manage its harvest can include implementing closed seasons, quotas (or bag limits), size limits, restricting use of certain fishing gear, having protected areas or stopping harvest completely – at least temporarily. When making these decisions we need to understand the current population levels (all around the world), the biology of the species, and have an appreciation for the extent of all the threats the species faces.
So the question is -  given what we know about sea turtles, are we willing to change how we use them now, including foregoing some of the benefits they can provide, so that in the future, sea turtles can be enjoyed in multiple ways by future generations?
A young green turtle found on the south coast of Trinidad that died due to fibropapilloma – a disease caused by a virus closely linked with water pollution (Michelle Cazabon-Mannette)

Note: Currently all five sea turtle species found in Trinidad and Tobago are legally protected under the Environmental Management Act, Environmentally Sensitive Species Rules (Legal Notices 2014), which carries a maximum fine of $100,000 and imprisonment for two years for adversely impacting a sea turtle.

Dr Michelle Cazabon-Mannette in her element, photo by Ryan Mannette