Abundance and exploitation of loggerhead turtles nesting in Boa Vista island, Cape Verde: the only substantial rookery in the eastern Atlantic

Abstract

The main nesting area for loggerhead turtles in the eastern Atlantic is in the Cape Verde Islands, largely restricted to the island of Boa Vista. Extensive monitoring demonstrated a globally significant population for the species despite a sustained high level of anthropogenic take of nesting females for local consumption. Through an extensive stratified monitoring program across the island in the seasons 2007-2009, we estimated a total of 13 955, 12 028 and 19 950 clutches in the 3 years, respectively. These values indicate that the mean number of nesting females averaged 3700. Considering that a female breed, on average, every 2.4 years, we estimate that the overall number of adult females in the population during these three seasons was 8900. These levels are much higher than those suggested in previous studies which were more constrained in spatial coverage. Our findings indicate that Cape Verde hosts the third largest nesting aggregation for this species in the world after the south-eastern US and Oman, with some sites having a particularly high density of nests, facilitating targeted monitoring and conservation. Consumption of sea turtle meat is a traditional practice in Cape Verde that continues despite national sea turtle protection laws. We estimated that 36, 18 and 5% of nesting females were harvested in the 3 years of the study, respectively. Increasing beach protection and monitoring, ongoing educational programs and cooperative projects with local communities are urgently needed to further safeguard the only major loggerhead nesting aggregation in the eastern Atlantic.

Nano-tags for neonates and ocean-mediated swimming behaviours linked to rapid dispersal of hatchling sea turtles

“…Fieldwork was conducted on the island of Boa Vista, the easternmost Cape Verdean Island (figure 1a) which supports up to 90% of the archipelago's loggerhead turtle nesting activity [33]. Hatchlings were obtained from a hatchery and natural in situ nests.…”

“…[18,22,23] with (ii) recently trailed at sea acoustic tracking [31] and (iii) high-resolution ocean model data [32]. We focused on the Cape Verde Islands which host the World's third largest [33], and highly philopatric [34] nesting population of loggerhead turtles which are genetically isolated from other Atlantic and Mediterranean rookeries [12]. Owing to the oceanic location of these islands, this nesting aggregation is exposed to very different ocean current regimes than coastal mainland sites where studies into loggerhead turtle hatchling swimming behaviour have focused.…”

“…Interestingly, in Boa Vista, ca 90% of turtle nesting occurs on the eastern half of the island [33] where the continental shelf is at its narrowest (less than 10 km; figure 1) and model-derived current flows were fastest (averaging more than 14.4 m min 21 ; figure 2). Relatively little nesting activity occurs in the west and north of the island [33] where the shelf extends twice the distance and current flows were half the speed.…”

Revisión de los conocimientos actuales sobre las tortugas marinas en el Archipiélago de Cabo Verde: Review of current knowledge about sea turtles in the Archipelago of Cape Verde

“…La presencia de tortuga boba se ha corroborado en todas las islas y algu- nos islotes del archipiélago, pero con una abundancia muy diferente. En torno al 90% de la anidación que existe se encuentra concentrada en la isla más oriental, Boavista, donde se estima una abundancia entre 2007 y 2009 de entre 12.000 y 21.000 nidos anuales MARCO et al, 2010b;MARCO et al, 2012). Las islas de Maio, Sal y São Nicolau albergan un número mucho menor de nidos, con alrededor de un máximo de 300-1000 nidos anuales por isla (LINO et al, 2010;CO-ZENS, 2009).…”

“…Además, el dramático declive de la anidación en otras islas, el uso generalizado de vehículos todo terreno y la llegada de multitud de trabajadores del continente para las obras de nuevos hoteles con sueldos muy bajos, ha acentuado la presión de caza sobre las tortugas durante su desove en los últimos años. La crítica situación alcanzada en 2007 a causa de la descontrolada matanza ilegal de hembras en playa MARCO et al, 2012), promovió un mayor compromiso e implicación por parte de organizaciones nacionales, regionales e internacionales para la conservación de las tortugas marinas en el archipiélago. El esfuerzo de protección y sensibilización de los últimos tres años parece estar dando algunos frutos incipientes, pero hay que incrementar las iniciativas de protección y cooperación al desarrollo sostenible de la población para garantizar la supervivencia de esta población atlántica tan emblemática.…”