How turtles benefit Seychellois

The Seychelles is home to nesting populations of two sea turtle species, the green turtle (chelonia mydas) and the hawksbill turtle (eretmochelys imbricata).

In fact, Seychelles hosts one of the five largest remaining populations of the hawksbill turtle

in the world and has the largest population of nesting hawksbills in the Western Indian Ocean. These amazing reptiles have been around since before the time of the dinosaurs, some 100 million years.

The International Union for the Conservation of Nature (IUCN) redlist of threatened species, states that the green turtle is considered as endangered while the hawksbill turtle is classed as critically endangered.

This is due to worldwide populations of these species declining in enormous numbers, so much so that we have lost up to 67% of the global population of nesting female green turtles and up to a staggering 87% of the global population of nesting female hawksbill turtles over the last three generations. Hawksbill turtles have been particularly badly affected in the Indian Ocean which has seen a decline in nesting females of 93% between 1870 and 2005. Nesting females have been completely wiped out from mainland Mauritius, where the last known nesting attempt was in the mid-1970s.

You may think that you see plenty of turtles in the waters around the inner Seychelles islands but you are very wrong. Compared to the population sizes that used to be found here, we have very little left. The turtles in Seychelles have been studied in great detail over many years by Dr Jeanne Mortimer. She has found that Seychelles itself has lost 65% of its nesting female green turtles and 25% of its nesting female hawksbill turtles. The loss of hawksbills would be so much higher if it weren’t for the hard work put into protecting the nesting beaches on Cousin Island, (Nature Seychelles) and Aride Island Nature Reserve (Island Conservation Society) which have been fully protected since the early 1970s and seven small private islands which have had intermediate protection since 1979. 

Dr Mortimer said simply by stopping people from killing turtles on the beaches and planting plants favoured by nesting females, Cousin and Aride have managed to increase their nesting turtle numbers by an amazing 389%. However, this is not enough to stop numbers, especially of green turtles, in Seychelles as a whole from declining. If we want to prevent our nesting Green and hawksbill turtles from becoming locally extinct such as on mainland Mauritius, we must stop killing them on all the islands and rehabilitate the remaining nesting beaches. Cousin and Aride have shown that this is a simple and very effective way of conserving these beautiful creatures.

Reasons for declines in population

Killing of nesting females, foraging adults, juveniles and eggs for human consumption - e.g. according to the University of Florida, exploitation of green turtles for food began in Bermuda in the early 17th Century and after two centuries, the nesting colony had become extinct. It has been illegal to disturb, harm or kill turtles in Seychelles, as well as to possess any of their products including meat, shells, eggs and calipee since 1994.

Breaking the turtle laws can result in a fine of up to R500,000, minimum 2 years in prison and confiscation of vessels and gear.

Degradation of nesting habitat – includes beach development such as the building of hotels and restaurants which removes plants favoured by nesting females, takes up space on the beach, increases levels of disturbance by people on the beach and creates light pollution where lights on the beach at night scare away female turtles and cause hatchlings to become confused and head away from the sea which ultimately causes them to die.

Degradation of the marine environment – includes pollution with chemicals, plastic bags that are mistaken as jellyfish and eaten (hawksbill) and destruction of coral reefs.

Tortoiseshell trade – according to Dr. Mortimer, 6, 569kg of tortoiseshell (hawksbill shell) which is equal to 8, 877 hawksbill turtles, has been exported from Seychelles to Japan since 1950. Although this trade has been banned, we are still feeling the effects.

Accidental by-catch in marine fisheries – entanglement in gill nets is believed to be the most significant fisheries related threat to hawksbill turtles in Seychelles.

Turtle biology - only 1 in 10,000 turtle hatchlings is estimated to survive to adulthood and it takes roughly 30-35 years for them to reach maturity and be able to breed so it takes a very long time for adult turtles that have been killed to be replaced in the population.

How turtles benefit Seychellois

Other than being beautiful and fascinating to watch and for attracting tourists to Seychelles, turtles can directly benefit locals and fishermen in particular.

It is a fact that green turtles are beneficial to the health of seagrass (also referred to as turtlegrass) beds due to the way that they feed on them. They keep the grass blades short and prevent turtlegrass wasting disease by enabling an efficient mode of nutrient transfer.

A research paper published in the Proceedings of the National Academy of Sciences, USA in 2001 showed that the vast majority of reasons behind the huge die-off of seagrass beds in Florida Bay are due to the large reduction in green turtle numbers in the area. In Seychelles, the seagrass beds host populations of fish commonly caught for consumption such as rabbit fish (kordonnyen), surgeonfish (sirizyen) and sand-wrasses (bef).
 

 

Hawksbill turtles are one of fewer than a dozen vertebrates known to specialise their feeding on sponges. Sponges are well known to compete strongly with corals for space on reefs, and scientists from the National Oceanic and Atmospheric Administration (NOAA) found them to be superior competitors in 80% of cases. As such, it has been concluded that Hawksbill turtles can have a strong effect on reef diversity, recovery time and succession by removing sponges that would otherwise inhibit new coral growth. After the well documented coral bleaching event of 1998, Seychelles’ coral reefs need all the help that they can get if they are to recover and continue to attract the tourist trade upon which Seychelles is dependent.

The relationships between hawksbill turtles, sponges, reef fish and coral reefs have been studied by several scientists over many years, notably Dr Anne Meylan. 

Dr Meylan found that hawksbill turtles not only remove sponges by direct consumption, but also make the soft inner parts of sponges available to fish after breaking through the tough outer layer.

Fish that would benefit from this in the Seychelles include two species of angelfish, a rabbitfish and the Moorish idol (Zanctus cornutus). Angelfish and Moorish idols are very popular with divers and snorkelers and also provide food for larger fish which in turn can be caught and eaten or sold. It is the general scientific consensus that through the removal of sponges, Hawksbill turtles can increase reef recovery time, providing larger areas of reef to support greater numbers of reef dependent fish and their predators e.g. snappers, groupers and parrotfish – all of which are eaten in Seychelles.

Sea turtles are ancient, beautiful creatures that can help Seychellois by attracting tourists, aiding reef recovery and indirectly providing fishermen with greater numbers of fish. As it has been shown by islands such as Aride and Cousin, these animals can be effectively protected and as such, it would be a real shame on us if we let them disappear from other inner islands.

Contributed by Georgia French, Marine Conservation Society Seychelles project coordinator