Globally important refuge for the loggerhead sea turtle: Maio Island, Cabo Verde

Abstract

One of the largest nesting colonies of the Vulnerable loggerhead sea turtle Caretta caretta is in Cabo Verde. Here we present the first comprehensive study of loggerhead turtle nesting on the island of Maio in Cabo Verde. During 2016–2019 we monitored 38 km of undeveloped sandy beaches that have minimal artificial lighting and where all nesting on Maio takes place. We counted 4,063 nests in 2016, 5,429 in 2017, 14,364 in 2018 and 7,937 in 2019. The estimated total number of females was 1,016, 1,357, 3,591 and 1,984 in each of these years, respectively. Our findings suggest there are more loggerhead turtles nesting in Cabo Verde than previously estimated, and that this could be the species’ largest nesting subpopulation (followed by Florida, USA and Oman). The inter-annual hatching success (the proportion of eggs producing hatchlings) was 29–38% for the whole island but varied between sites. Our study of 250 clutches showed that flooding affected 38–61% and predation by crabs 40–42%, with hatching success on different beaches in the range of 1–59%. Poaching of eggs was rare (< 2% of clutches), but dogs predated 68.4% of all clutches on the beach nearest the largest human settlement. We evaluated different nest management strategies at multiple sites and estimated productivity of hatchlings (the number of hatchlings that would reach the sea for each management strategy), finding that hatcheries are not always the best option for nest management. As the beaches on Maio are relatively undisturbed, and there is a high abundance and density of turtle nests, the island should be protected as a globally important site for the conservation of the loggerhead turtle, and of coastal biodiversity more broadly.

Strategic nest site selection in one of the world's largest loggerhead turtle nesting colonies, on Maio Island, Cabo Verde

“…Here we describe the degree of nesting beach selection and the consistency of intra-beach site selection for egg deposition over 8 years in one of the largest loggerhead turtle Caretta caretta colonies: Maio Island on Cabo Verde, West Africa (Cozens et al, 2011; Dutra & Koenen, 2014; Patino-Martinez et al, 2022a). In the last decade (2012–2021) the number of nests has increased on Maio Island, with a mean of 19,415 ± SD 16,450 nests per season during 2017–2021 (Patino-Martinez et al, 2022b).…”

Ghost crab predation of loggerhead turtle eggs across thermal habitats

“…Maio Island represents a great input for the loggerhead Northeast Atlantic subpopulation (Patino-Martinez et al, 2021) and, given the high mortality rates among in situ clutches reported here, it is recommended that protection measures are implemented. In the past, clutches and turtles were extensively poached by local communities (Cabrera et al, 2000;Lino et al, 2010;Cozens et al, 2011;Marco et al, 2012;Hancock et al, 2017), contributing to population decline.…”

“…The North East Atlantic subpopulation of loggerhead sea turtles (C. caretta), is listed as Endangered by the IUCN Red List of Threatened Species (Casale and Marco, 2015). Recent findings suggest a higher number of loggerhead turtles nesting in Cabo Verde than previously estimated, and that this might be the largest nesting subpopulation of this species globally (Patino-Martinez et al, 2021). However, the vast majority of the nests are concentrated in the Cabo Verde archipelago, making this subpopulation particularly vulnerable to habitat loss and degradation (Casale and Marco, 2015).…”

“…However, the vast majority of the nests are concentrated in the Cabo Verde archipelago, making this subpopulation particularly vulnerable to habitat loss and degradation (Casale and Marco, 2015). Within Cabo Verde, Maio Island, hosts an important proportion of the nests, with an estimate of 4063 to 14,364 nests per year, between 2016(Patino-Martinez et al, 2021. The nesting beaches of Maio Island are heterogeneous in sand coloration; with light, mixed and dark sand, and loggerhead sea turtles nest on all of them.…”

Effect of body size on the long-term reproductive output of eastern Atlantic loggerhead turtles Caretta caretta

“…Neophytes are usually smaller than remigrants in marine turtles (Lamont et al 2014, Stokes et al 2015; hence, increasing numbers of small nesting females might suggest improved recruitment to the adult population (Arendt et al 2013, Omeyer et al 2021. Nest counts have increased recently across the archipelago, and during the 2018 nesting season, the number of nesting loggerhead turtles at Cabo Verde tripled in comparison to the previous year (2017), which was a record year for the NN registered (Marco et al 2012a, 2018b, Laloë et al 2020, Patino-Martinez et al 2022). This could be interpreted as evidence of an increased population size, but caution is needed because increased NN might also result from changes in the RI and the total number clutches laid per season, even if population size remains unmodified (Hays et al 2022).…”