The nesting of sea turtles triples in the colony of Cape Verde

The nesting of sea turtles triples in the colony of Cape Verde https://noticiasdelaciencia.com/upload/images/12_2018/1688_45754.jpg?15

The nesting of sea turtles triples in the colony of Cape Verde





Nesting of the threatened or turtle turtle, a threatened species, has tripled during the summer of 2018 compared to the previous record of nests of the last 20 years in the colony of Cape Verde, the only place where it nests in the entire eastern Atlantic, According to a work led by researchers of the Higher Council for Scientific Research (CSIC) at the Doñana Biological Station (Spain). The most likely hypothesis is that this recovery could be due to a significant increase in the number of young females associated with nesting protection initiated 20 years ago in Cape Verde.

 

This protection on the beaches with a very active participation of the CSIC caused a very significant increase in the birth of turtles on the beaches and now they would be starting to mature sexually at 15-20 years of age. "This is excellent news that could mean the beginning of the long-awaited recovery of this threatened population," says Adolfo Marco, a researcher at the Doñana Biological Station, who led the scientific study. "Recently, the International Union for the Conservation of Nature (IUCN) updated its assessment of this species and considered that the population of Cape Verde was in danger of extinction, while the rest of the Atlantic populations were greatly improving their status. conservation ", explains Marco.

 

"This population was cataloged as one of the 11 most threatened in the world. The last 20 years of conservation efforts seemed not to be paying off. However, the 2018 data can be a very hopeful turning point in the future of this important colony of sea turtles, "adds the researcher.

 



 

Specimen of marine turtle camouflaging its nest. (Photo: Adolfo Marco)

 

"The number of nests on the beaches is considered a reliable estimator of the total number of adult females of a population and, therefore, of their conservation status," explains Marco. A strong increase in the annual number of nests can be due to the fact that the number of adult females has increased. However, it can also be explained by other causes related to the complex reproductive strategy of sea turtles.

 

Each adult female rarely spawns in two consecutive seasons and rests without spawning between 2 and 5 years. Therefore, a very high synchronization of many females of the population in the same year could cause an increase in the number of nests without varying the total number of adult females of the population.

 

"However, during 2018 less than 0.5% of the adult female breeders had been identified in 2017. Therefore, there does not seem to have been such a synchronization," says Marco. "In fact it can be said that the 15,000-20,000 females that may have spawned this year in Cape Verde must add the 6,000-8,000 that spawned in 2017, which are overwhelmingly different. Excellent news, because about 10 years ago it was estimated that the total number of breeding females of the population could be between 8,000 and 10,000 individuals. Now we would have at least double, "he adds.

 

Another alternative explanation could be related to a change in the annual number of nests per female. "Each turtle female spawns several times during a season every 14 to 18 days. In Cape Verde it has been estimated that each female can lay between 4 and 6 nests each year. One might think that this annual frequency of nests could have increased, explaining that nest increase of 2018 without a change in the number of females. An increase in food at sea could have caused a

 

very high level of fat reserves in females that allow them to make more nests per season. However, the start and end of this season have been similar to the rest of previous years and, therefore, it seems impossible that each female has had time to put more than 6 consecutive nests, as usual. The temporary spawning pattern during 2018, as well as the number of registered nests per female are very similar to those of other years, "says Marco.

 

One might think that females from other Atlantic populations have arrived massively, but this is extremely unlikely, because genetic studies show that the fidelity of the turtles to their beach of birth is very high, with very strong reproductive isolation between different populations. In addition, no significant decrease in the number of females spawning in neighboring populations has been detected.

 

It seems that the only explanation for this very important increase in nests is that the number of adult females of this population has really increased in the last two years. What could have happened for this increase? The mortality of adult females could have been reduced significantly. However, the number of adult female remigrants has not been especially high in 2018 or 2017. On the contrary, thousands of females tagged in the population in previous years have not been re-located. The mortality of females on beaches has been significantly reduced, but the same may not have happened at sea. We also have no reason to believe that the mortality rate of juveniles at sea has been reduced, since the most important anthropogenic threats, such as accidental fishing or interaction with plastics, have not diminished.

 

"The most likely hypothesis of the increase in adult females is a very significant increase in the production of females on the beaches in the last 20 years," says Marco. "The very high number of neophyte females, who arrived in 2017 and especially in 2018 for the first time to breed in Cape Verde, seems to support this explanation. Thousands of young females have joined the breeding population for the first time and can explain this significant increase in the number of nests, "he adds.

 

This last explanation may make sense on the 20th anniversary of the beginning of turtle nesting protection in Cape Verde. 15-20 years is the age around which the sexual maturation of this species occurs.

 

"We will have to have patience to see if these positive figures are consolidated. If the most probable hypothesis is true, the prediction for the coming years is a continuous increase in the recruitment of new breeding females. It will be very important to maintain the preservation effort so that other threats do not slow down or reverse this hopeful tendency of recovery that seems to start now, "says Marco.

 

In this sense, the very important reduction of turtle hunting on the beaches is also encouraging. In 2018 the number of turtle hunters and the sale of turtle meat on the island seems to have decreased significantly compared to previous years. The implementation in 2018 of the new law that protects turtles and penalizes their hunting much more effectively, could be bearing fruit.

 

The main funders of this research and the protection of turtles in Cape Verde in all these years have been, in addition to the Biological Station of Doñana, the Ministry of Environment of Andalusia and the Canary Islands, the AECID, the MAVA Foundation and the Service of United States Fish and Wildlife (USFWS) through the Marine Turtle Conservation Fund. (Source: CSIC / DICYT)
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