seaturtle.org : MTN : ARCHIVES : Sign In

Four species of sea turtles occur in and around Santiago Island, Cape Verde. The loggerhead (Caretta caretta) is the only species that has been confirmed nesting and is also encountered in coastal waters. The green turtle (Chelonia mydas) is present in the waters of Santiago, but only as juveniles. Some are captured incidentally in fisheries, and there are a few anecdotal reports of fishermen directly targeting green turtles for food, although their small size (25 to 40 cm CCL) makes them less appealing than large juveniles or adults. The leatherback (Dermochelys coriacea) is rarely sighted in the waters of Santiago, although interviews with elderly fishers suggest that they were more abundant in the past. The hawksbill (Eretmochelys imbricata) is also rare, and only records of juveniles have been reported from the waters of Santiago. Since 2002, all sea turtles and their habitats are protected by law (Decreto-Regulamentar n° 7/2002), but the consumption of sea turtle meat and eggs has not significantly decreased. National authorities are increasing their efforts to reduce sea turtle captures.

In May 2007, a research project was established to provide information on which to base sustainable management of sea turtles in Santiago Island. A monitoring program was initiated in which all beaches on Santiago were visited at least twice during July-August, which largely encompasses the main loggerhead nesting period (July to September) for Cape Verde (Cejudo et al. 2000). Two sandy beaches, Praia Baixo and Achada Baleia, in the southeastern section of the island (Fig. 1), were patrolled between 21 May and 9 November for sea turtle nesting activity, and Mangue beach was regularly patrolled during May-July. Early morning patrols were carried out daily to check for signs of crawls, nests and hatchling emergences. In addition, we conducted nighttime patrols for nesting females and/or hatchling emergences from nests, between 22:00 and 05:00, six nights per week, from early July through late September, in Praia Baixo and Achada Baleia beaches. Nighttime patrols in Mangue beach were restricted to July only.

We recorded nesting date, GPS location, egg count during oviposition, minimum curved carapace length (CCL) and curved carapace width (CCW). We also noted any flipper tags, injuries, epibionts, or apparent signs of disease of nesting females. We did not record information from females that returned to sea without oviposition. For nest emergences, we recorded the date of emergence and scheduled nest excavations at least 24 hours after the first signs of emergence. Each nest was opened and contents sorted into empty egg shells, unhatched eggs with visible dead embryos, unhatched eggs with no visible embryos, and live hatchlings remaining in the nest (following Miller 1999 and Varo-Cruz et al. 2006). We also kept records on any apparent predation or harvest of turtles, indicated by signs of only single track up the beach (without a returning track), and signs of turtles being dragged away from the beach. Whenever possible, we confirmed these records with interviews with local people. We also intervened whenever possible to avert capture of nesting females.

Opportunistically, we measured CCL and CCW of juvenile green turtles when they were accidentally captured by fishing gear and landed at the Achada Baleia beach. Fishers kindly cooperated with us, offering the animals alive, after we explained the urgent need for new sea turtle friendly behavior. Juvenile green turtles were returned to the sea at the same beach, after carapace measurements, in the fishers’ presence.

The three goals of this project were as follows:

i. To characterize the status of sea turtles and their conservation in the Santiago Island, from ecological, biological and anthropological views.
ii. To survey nesting activity and nesting seasonality of loggerheads in different beaches.
iii. To assess the primary threats to sea turtles in the Santiago Island and make recommendations for their mitigation.

This paper provides an overview of the main biological and ecological results from the first year of research.

In the past, the beaches of Santiago island (n=53) were naturally abundant, variable in characteristics and generally of medium (1 to 2 km) or short length. In recent years, a large number of beaches have been damaged (Fig. 1), as a result of intense sand extraction, mainly for local construction projects (Cape Verde tripled its permanent population between 1951 and 2005), or for the growing tourism industry (Cape Verde opened three new international airports between 2005 and 2007). Only 18 beaches remain that are considered suitable for nesting sea turtles (Fig. 1). The disappearance of many sandy beaches may be an important factor in the apparent decrease of the nesting loggerheads at Santiago Island.

Figure 1. Map of Santiago Island, Cape Verde. Data were acquired from several sources, including: i. interpretation of airborne ortophotomaps, scale of 1:10,000 (Digital Cartography Project of Cape Verde); ii. analysis of the Military Map of Portugal (Cape Verde Province), scale of 1:25,000, dated of 1969 to 1974; iii. nearly exhaustive visit to the entire coastal strip of the island; iv. complementary open interviews with residents, whenever possible.

In Cape Verde, extraction of sand from beaches was forbidden by law in 2002 (Decreto-Lei n° 2/2002). However, regulation and enforcement remains a challenge in remote areas but recent governmental enforcement of the ban on sand extraction is improving and demand for sand in local construction projects is being met by increased importation from Mauritania, Senegal and Morocco.

In 2007, loggerheads nested on nine beaches (Fig. 1). Of the remaining undamaged beaches, four are heavily used by beach visitors and fishers and five have high levels of pollution (light and/or chemical). Praia Baixo beach (Fig. 1), in the southeast of the island, is about 1.4 km long, has dark sand and a gently seaward slope. In addition to the presence of tourists in the beach on weekends, Praia Baixo also suffers from problems of artificial nighttime lighting. In contrast, the beaches of Achada Baleia (600 m long) and Mangue (400 m long) have darker sand and a steeper slope. There was no artificial lighting at Achada Baleia or Mangue beaches. Praia Baixo and Achada Baleia beaches have permanent military patrols, whose main task is to prohibit any illegal extraction of sand. Enforcement is better in Praia Baixo, resulting in minimal sand extraction, whereas in Achada Baleia, sand continues to be extracted in fairly large quantities, due to less stringent enforcement. Access to Mangue beach is controlled by a local landowner who does not allow any sand to be extracted, for fear of increasing salt intrusion into the groundwater.

Table 1. Number of loggerhead clutches laid in three beaches, in southeastern Santiago Island, Cape Verde, during the 2007 nesting season. n/a indicates no monitoring was conducted during that month.

During the three month (July-September) survey period, relatively few clutches were laid (Table 1). The mean size of nesting females that we encountered was 82.3 cm ± 2.1 SD CCL (range: 79-86 cm; n=21) and 77.7 cm ± 2.7 SD CCW (range 74-82 cm). However, as we do not tag nesting females and only encountered untagged turtles, a bias from repeated measurements of the same individuals may have occurred. These values include four carapaces of recently dead nesting females, found on Medronho beach, northern end of Santiago Island (Fig. 1). Our values are similar to mean sizes recorded for nesting loggerhead females in Boavista Island, Cape Verde (López-Jurado et al. 2003; Hawkes et al. 2006). However, we did not find any nesting females greater than 100 cm CCL, as reported for Boavista (Hawkes et al. 2006). Remoras (Remora remora) were observed on the carapaces of three nesting females, and gooseneck barnacles (Lepas anatifera) were observed on four nesting females. No other epibionts were observed.

The mean clutch size was 81.5 eggs ± 14.7 SD (range: 34-102; n=23). Compared to other nesting populations in the Atlantic, the mean clutch size in Santiago appears to be low (Cejudo et al. 2000; Tiwari & Bjorndal 2000), although loggerheads nesting in Cyprus appear to produce fewer eggs on average (Broderick et al. 2003).

Table 2. Hatching success and incubation period in 2007 from two beaches in southeastern Santiago Island, Cape Verde.

Fourteen clutches that were incubating in Praia Baixo and Achada Baleia beaches were lost or destroyed before hatching (Table 2). Causes for nest loss included collection by people, predation by stray dogs, heavy rain, tidal overwash and compaction by heavy vehicles on the beach. For the nests that did successfully reach the end of incubation, emergence success was >70% on the two beaches (Table 2). The extensive use of Praia Baixo beach by visitors on weekends did not appear to negatively impact egg development, but hatchlings misorientation from artificial lighting did occur (n=2).

Fewer clutches successfully hatched on Achada Baleia than on Praia Baixo beach, which may have been due to seasonal effects on hatching success: 3 nests laid in September in Achada Baleia beach had high numbers of undeveloped eggs (54% of all eggs). One nest laid in Praia Baixo beach in September also had a high rate (29%) of undeveloped eggs.

In eight instances nesting females were illegally harvested at Praia Baixo beach (three of which were successful captures and the turtles were killed), and at Achada Baleia beach 21 attempts were made (17 were successful). In Mangue beach, during July, there were 13 successful attempts. Thus, a total of 43 loggerhead females were killed on the three beaches during the 2007 nesting season. There were fewer successful captures of nesting females in the later months of the nesting season, likely due to an increased awareness of our patrols and also the military patrols in the beaches. There is no available information on captures of nesting turtles in the other six beaches.

Five juvenile green turtles stranded during the 2007 nesting season after being killed at sea by fishers (n=1) or caught accidentally in fishing gear (n=4). The latter four turtles were returned alive to the sea. The mean size of the five green turtles was 35.9 cm CCL (range: 25.0-47.0 cm) and 32.3 cm CCW (range: 21.5-42.0 cm).

Loggerhead nesting continues to occur in some parts of Santiago Island, but based on informal interviews with elders, current numbers are reduced relative to historic levels. Anthropogenic pressures, such as sand extraction, nighttime lighting, and direct harvest, continue to be serious threats to the existence of a nesting population in Santiago Island. In the future, it is recommended that there be not only more patrols (and associated protection of nesting females) on Santiago Island sandy beaches, but also an education campaign about sea turtles and their natural history. Protecting turtles and their habitats will benefit the inhabitants of Santiago Island by ensuring that their natural heritage is maintained and enjoyed for generations to come.

Acknowledgments: I thank the following groups and individuals: the Oceanário de Lisboa, S.A. for providing the full support to the “Iniciativa para a Gestão Integrada de Tartarugas Marinhas na Ilha de Santiago, Cabo Verde”; the Algarve University (Portugal); Elson Martins and Severa Reis, for the day-to-day help and collaboration during the in-situ “beach work” campaign; the Associação Nacional dos Municípios Caboverdianos (ANMCV) for all the facilities during the ortophotomaps analysis and interpretation; the Editor and reviewers of MTN, for the relevant contribution to increase the paper quality.

BRODERICK, A.C., F. GLEN, B.J. GODLEY & G.C. HAYS. 2003. Variation in reproductive output of marine turtles. Journal of Experimental Marine Biology and Ecology 288: 95-109.

CA’ DA MOSTO, A. 1507. Navegações 1ªe 2ª. In: Instituto Nacional de Investigação Científica. 1988. Descobrimentos Portugueses. Lisboa. I Supl. pp. 234.

CEJUDO, D., I. CABRERA, L.F. LÓPEZ-JURADO, C. ÉVORA & P. ALFAMA. 2000. The reproductive biology of Caretta caretta on the Island of Boavista (Republic of Cabo Verde, West Africa). In: H.J. Kalb & T. Wibbels (compilers). Proceedings of the 19th Annual Symposium on Sea Turtle Biology and Conservation, NOAA Tech Memo NMFS-SEFSC-433, pp. 244-245.

COSTA, F.L. 2004. Contribuições para o conhecimento dos processos erosivos em Cabo Verde. GeoINova 9: 215-244.

HAWKES, L.A., A.C. BRODERICK, M.S. COYNE, M.H. GODFREY, L.F. LOPEZ-JURADO, P. LOPEZ-SUAREZ, S.E. MERINO, N. VARO-CRUZ & B.J. GODLEY. 2006. Phenotypically linked dichotomy in sea turtle foraging requires multiple conservation approaches. Current Biology 16: 990-995.

LÓPEZ-JURADO, L.F., N. VARO-CRUZ & P. LÓPEZ-SUÁREZ. 2003. Incidental capture of loggerhead turtles (Caretta caretta) on Boa Vista (Cape Verde Islands). Marine Turtle Newsletter 101:14-16.

MILLER, J.D., C.J. LIMPUS & M.H. GODFREY. 2003. Nest site selection, oviposition, eggs, development, hatching, and emergence of loggerhead turtles. In: A.B. Bolten & B.E. Witherington (Eds.). Loggerhead Sea Turtles. Smithsonian Press, Washington D.C. pp. 125-143.

MONOD, Th., A.T. MOTA & R. MAUNY. 1951. Description de la Côte Occidentale d’Afrique (Sénégal au Cap de Monte, Archipels) par Valentim Fernandes (1506-1510). Centro de Estudos da Guiné Portuguesa, Bissau. pp.

TIWARI, M. & K.A. BJORNDAL. 2000. Variation in morphology and reproduction in loggerheads, Caretta caretta, nesting in the United States, Brazil, and Greece. Herpetologica 56: 343-356

VARO-CRUZ, N., A.L. LOZA, Ó.A. LÓPEZ-LÓPEZ & L.F. LÓPEZ-JURADO. 2006. Manual para trabajos prácticos con tortugas marinas nidificantes en Cabo Verde. Gran Canaria. 54pp.

Four 10 min. documentaries are available for free vodcasting distribution (URL feed to iTunes subscription: <http://www.al-bloc.net/vodcasting/turtles.xml>). The WebVDocs are:

Histories without Turtles (“Histórias sem Tartarugas”)
Histories with Turtles (“Histórias com Tartarugas”)
I. Cc Ovipositions (“Posturas de Caretta caretta”)
II. Frenzy of Life (“Frenesim de Vida”)
III. Life and Death Contrasts (“Contrastes de Vida e Morte”)

They are also available at <https://seaturtle.org/multimedia/>