Guest Blog

By Adolfo Marco, Doñana Biological Station, CSIC

Twenty years later, loggerhead sea turtles Caretta caretta nesting in Cabo Verde, seem to recover following decades of poaching and disturbance on their breeding sites. During this year’s breeding season, the number of loggerhead turtle nests in Cabo Verde tripled (approximately) compared to 2017. This is excellent news meaning perhaps that a long-awaited recovery of this threatened population is happening.

IUCN recently updated the assessment of this species on its Red List of Threatened Species. It now considers that the population of Cape Verde, unique throughout the eastern Atlantic, is in danger of extinction. Cape Verdean loggerheads are categorised amongst the 11 most threatened turtles in the world and until very recently the conservation efforts of the last 20 years seemed vain. However, this year’s data show a very hopeful turning point in the future of this unique sea turtle population. Turtles are long-living animals and this example clearly shows that only long-term strategies supported by dedicated donors such as the MAVA Foundation pay-off. MAVA continues to support work on green and loggerhead turtles as part of its action plan to minimise disturbance and eradicate illegal harvesting on key nesting sites.

Making a long story short

Thanks to dedicated efforts of NGOs and the Cape Verdean authorities, despite nest flooding, high natural predation rates, and poaching, the number of loggerhead turtle nests in Cabo Verde has increased (Figure 1).

Figure 1 – Number of accumulated daily nests at the beach of Joao Barrosa (Turtle Natural Reserve, Boa Vista Island, Cabo Verde) during 2018 compared to 5 preceding years.

How to explain this sudden increase?

The protection of the most important nesting beaches of Cabo Verde began in 1998. This year, we celebrate the 20th anniversary of the beginning of turtle protection on the beaches. Coincidentally, loggerheads reach sexual maturation at 20 years of age!

Following decades of intensive poaching and unregulated tourism and other human activities on the beaches, an important number of females have been returning safely to sea after laying. The loss of eggs and juveniles has also been reduced dramatically by translocating thousands of nests to artificial hatcheries. This has improved the productivity on the beaches from 1998 onwards and it is to be expected that there would be a higher number of adults in the population 20 years later, even knowing that the mortality at sea most likely hasn’t decreased.

Adult females rarely spawn for two consecutive years. Following an active breeding season, they usually rest without spawning for two to five years. However, it is known that sometimes huge numbers of females come ashore to lay in one particular year, without having a variation in the total number of adult females in the population. However, in our case, since a significant number of laying females is tagged every year we know that less than 0.5% of the adult females that nested in 2018 have also been identified on the beaches in 2017. These figures support our belief that we are not facing a sporadic synchronism episode. In fact, those 15,000-20,000 females that nested this year in Cape Verde are in addition to the 6,000-8,000 that nested in 2017, and this is excellent news. Ten years ago, it was estimated that the total number of breeding females in the population would be around 8,000 to 10,000 individuals. Now, we are probably dealing with at least twice as many!

Each female turtle lays several times during one breeding season, every 14 to 18 days. In Cabo Verde it has been estimated that each female may lay in different nests between 4 and 6 times per year. A potential increase of the food available at sea could have caused an accumulation of very high levels of fat reserves allowing the females to produce more eggs and built more nests this year. However, it seems impossible that a female digs more than seven nests per season and we know this did not happen since we tag a high percentage of females coming ashore allowing their individual identification.

The only explanation for such an important increase in the number of nests seems to be a higher number of adult females in the population. The increase in adult females is at least to a certain extent the result of an increased breeding success and higher productivity due to direct management and nest translocation. High numbers of new turtles arrived in 2017 and especially in 2018 to breed for the first time in Cabo Verde, which supports this hypothesis. Thousands of young females seem to have joined the breeding population for the first time which explains this important increase in the number of nests.

What’s next?

We still need further evidence; we must be patient and wait for 2019 before celebrating. If our hypothesis is confirmed, a continuous increase is expected in the following years with the systematic return of new breeding females. Meanwhile, we’ve got to keep reducing threats on the beaches and the surrounding waters where the turtles mate, hoping that this recovery trend continues.

In 2018, at least in Boavista, despite the large number of turtles on the beaches, the number of active hunters and the sale of turtle meat seems to be less significant than in previous years, thanks to the cooperation between NGOs, the National Directorate for the Environment (DNA) and the maritime police. A new surveillance brigade was established and new methodologies such as drones and search dogs have been tested with the support of MAVA.

Along with the implementation of new strategies to support local communities, promote, awareness and environmental education, a big step forward was the implementation by the government in 2018 of a new law that protects turtles and criminalizes their possession, hunting and trade. The great challenge for NGOs is to remain operational with the support of the State and motivated donors such as MAVA and the United States Fish and Wildlife Service (USFWS), willing to support long term conservation efforts.