Thursday, February 19, 2015

Bake and shark a threat to turtle conservation

Guest Post
by Marc De Verteuil

Trinidad & Tobago is famous for being at the forefront of sea turtle protection and for the delicious bake and shark. But what if eating shark puts turtles at risk? Healthy reefs need sharks to create ecosystem balance. Even turtle populations can cause problems when they do not have predators to keep them in check. T&T banned the hunting of marine turtles in 2011 but what effect can this have on a wider marine ecosystem in which sharks are driven to extinction?

This question struck a cord with me after a dive at Macqueripe Bay, in the proposed Tucker Valley National Park, Chaguaramas. Within a relatively small area I saw five turtles—two critically endangered hawksbill turtles (Eretmochelys imbricate) and three endangered green sea turtles (Chelonia mydas). Only one hawksbill was an adult. It a kept a weary distance, a result of pre-ban turtle hunting by spear fishermen.

The other four observed turtles had probably never experienced life before the hunting ban. None of them had ever faced the business end of a spear so fearless of humans they showed no avoidance behaviour. It seems that there is strong population growth. Will there be a time that there will too many turtles for the bay to support and will the absence of sharks then become a problem?

Sea turtle conservation has been successful throughout much of the Atlantic area. Simple conservation efforts like protecting turtles and turtle nesting beaches, the banning of gill nets and the introduction of Turtle Exclusion Devices (TEDs) has resulted in a growth rate of between 4-16 per cent for the green sea turtle population.

Green sea turtles are mostly herbivorous. Seagrass beds are like the meadows of the ocean. Grazing sea turtles eat large amounts of seagrass. Historically they played an important role in maintaining healthy seagrass beds by pruning the seagrass canopy and preventing the build-up of dead matter.

Green sea turtles were nearly hunted to extinction by humans and a knock on effect of their plummeting numbers may have been the mass die-off of seagrasses in the 20th century. Seagrass meadows offer important ecosystem services like habitat for many fish species and carbon sequestration. Sea turtle numbers have bounced back in Bermuda.

It is a conservation success but one that throws up a new challenge as sea turtles are overgrazing the seagrass beds. Some seagrass beds have been completely destroyed. The problem is that sea turtles are being reintroduced to an ecosystem that is completely altered by humans. Humans aside, sharks are the main turtle predators.

But overfishing has decimated their numbers and up to 25 per cent of shark species are in danger of extinction by the year 2050. Tiger sharks used to keep sea turtle numbers in balance, but they are now near threatened themselves. Pew Charitable Trust, based in Washington DC, is at the forefront of worldwide shark conservation and a major driver behind the establishment of shark sanctuaries.

Pew’s Angelo Villagomez explained to me that: “There was a study recently by Dr Mike Heithaus showing sharks regulate the behaviour of turtles, which in turn benefits the ecosystem. If there are no sharks, the turtles can overgraze seagrass beds, which can be important breeding and pupping grounds for fish, as well as carbon sinks.” Tiger sharks do more than just limit turtle numbers. They also alter their behaviour by influencing where turtles graze.

In the absence of sharks turtles will choose to graze the tastiest, most nutritious sea grass beds, which become overgrazed and then destroyed. When tiger sharks are in the area turtles behaviour is influenced by fear. They spend less time in the most desirable seagrass areas and do not overgraze. In order to protect sea turtles we must protect sea turtle habitat. Protecting sea turtle habitat means protecting the sharks that are turtles’ main predator.

Predators do not only affect numbers and health of prey, they also influence habitat, like seagrass beds. This is in no way a call to cull sea turtle numbers. Marine turtles are still faced with the threat of extinction. Sea turtle recovery will take many decades or longer. If the population is to recover to healthy levels we need to protect the different parts of the ecosystem with which sea turtles interact.

T&T is the number six exporter of shark fin to Hong Kong. This makes T&T a global player in the demise of sharks. This trade must be halted. Bake and shark is a national food, a culinary delight for which locals and visitors travel to Maracas beach. It is a tradition, but traditions must change when they become unsustainable. Please enjoy a sustainable alternative like bake and flying fish or bake and cheese. T&T tradition is eating delicious food, not eating endangered species.


Anonymous said...

Some things didn't quite make sense in the article. The tiger sharks are near threatned but most turtles are critically endangered. The sharks aren't smart enough to manage the turtle resource - they really could care less if they eat every last one. The critically threatened turtles required active management to get their numbers to start to recover - their numbers are just starting to recover. I am not saying kill all of the tigers going after the pregnant turtles but why not catch and release some of the tigers so the turtles can at least lay their eggs. The turtle populations probably will never recover to 5% of their numbers from 500 years ago - so it is rather unscientific to talk about the great potential for sea grass damage from a handful of critically endangered animals.
Also note that seas turtles have a very poor net reproduction rate - how many actually even make it to an adult state - far fewer % than the tiger sharks.
Wouldn't it be a big improvement to move sea turtles to the same near threatened status of the tiger sharks - then the sharks will actually have some turtles to eat - right now many of the turtles must be a very rare treat.

Yes top predators eat turtles and we are the biggest reason that everything is disappearing, however, we have saved many species from extinction such as the California condor and others - lets manage the turtles until their numbers rebound - then the sharks will have one of their favorite snacks to munch on also.

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