MASSIVE CAPTURE OF NESTING FEMALES IS SEVERELY THREATENING THE CABOVERDIAN LOGGERHEAD POPULATION Adolfo Marco 1, Oscar López 2, Elena Abella 1, Nuria Varo 2, Samir Martins 3, Pilar Gaona 1, Paula Sanz 1 and Luis Felipe López-Jurado 2 1
[email protected], Estación Biológica de Doñana, CSIC, Sevilla, Spain; ICCM (Gobierno de Canarias); 2 Instituto Canario de Ciencias Marinas, Las Palmas, Spain; 3 Cabo Verde Natura 2000, Sal Rei, Boavista, Cape Vert Punctual surveys
INTRODUCTION
Maximum number of nests
Loggerheads are the only sea turtle species with significant nesting activity in Cape Verde. This population has a significant degree of genetic (nuclear and mitochondrial) isolation with the closest American and Mediterranean populations ( Monzón-Argüello et al, submitted). The archipelago is also a feeding ground for Chelonya mydas and Eretmochelys imbricata.
Figure 1
It is the third largest loggerhead population in the world. Turtles nest in several islands from this archipelago but more than 90 % are using the island of Boavista.
MATERIAL AND METHODS
However, the capture of nesting females for human consumption is a spread practice in the local population that could be killing a significant percentage of nesting females every year. The severe decline of turtle abundance in other islands is now increasing the hunting pressure over the individuals that nest on Boavista.
During 2007 nesting season, we daily recorded the high density of nests laid in protected beaches (10 Km) in the southeast of the island of Boavista. We have also conducted four different surveys along the nesting season (from the end of June to the beginning of October) in the rest of the nesting beaches (aprox. 60 Km) counting all the nests laid in a single night. Then, we have estimated (using different criteria in every single night survey) the number of nests laid during the whole season on the island following the method proposed by Godley et al. (2001).
Figure 2 Figures 1 and 2. Number of nests and females in Boavista during 2007 nesting season.
RESULTS Around 1140 females were hunted while nesting. That means the 15 % of the estimated adult female Boavista’s population, the 35.6 % of the total number of females nesting in Boavista during 2007, and the 71 % of females nesting on unprotected beaches.
Estimated number of nesting females
Nesting beaches In Boavista
The carcasses of the 58 % of them were left on the beach. The 42 % were transported dead or alive to other sites.
Length (km)
Number of nests
End of July
End of August
Hunted females
Protected
10
˜ 8392
1600
1600
< 50
Unprotected
60
˜ 5951
1600
570
> 1100
TOTAL
70
1277314343
3200
2170
˜ 1140
Table 1. Comparison of nesting abundance and female mortality on beaches in the island of Boavista at the beginning and the end of the period of maximum nesting activity
Figure 3.
CONCLUSIONS +155
-1050
+40
huevos Figure 4.
Figures 3 and 4. Seasonal variation of the number of nests and nesting females on protected and unprotected beaches
Acknowledgements We would like to thank the following people for their contributions: Carlos Angulo, Juan Patiño, Rosa Mª García, Sonia Rodríguez, Núria Plantalech and Patrick Cardoso. We are also grateful to the following institutions: Instituto Canario de CienciasMarinas, Estación Biológica de Doñana, the Cape Verde government.
During the 2007 nesting season we have estimated that only around 3200 females have nested in the island, laying around 14000 nests. More than 1100 females have been killed or captured on unprotected beaches. To this severe mortality we have to add the death of females into the sea. If this mortality rate continues, the annual recruitment should be larger than the 25 % to guaranty the population stability In protected beaches the number of nests remained stable during the nesting season. However, in non-protected beaches and due to the strong nesting site fidelity within the season, the number of nests drastically decreased up to the 65 % during the second half of the nesting season. Unfortunately, some females that nest in the protected beaches will use unprotected ones during next nesting seasons. Thus, it is not possible of guarant ying the survival of any female protecting only part of the nesting beaches.
