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The olive ridley sea turtle Lepidochelys olivacea has been recorded in the Cape Verde Islands, but the most recent published data (1998-2000) are of stranded individuals and remains only. This article presents new data on olive ridleys recorded during the years 2001-2011 on Boavista and Sal islands. The presence of this species does not appear to be related to nesting activity. The possible geographical origin of these turtles is discussed. In addition, we propose some studies that could help to reinforce the conservation of sea turtles in West Africa.
On 31 August 2003, at 11:40 local time, c. 5 nm southwest of São Nicolau (16º33.1N, 024º27.7W), Cape Verde Islands, GT and PLS observed c. 20 Fraser’s Dolphins Lagenodelphis hosei Fraser, 1956 (Fig.1). The sighting was made under excellent weather conditions (sea state Beaufort 2 with sun) from the 39.6 m diesel engine powered oceanographic research vessel Taliarte during a two week cetacean survey conducted as part of the Hydrocarpo project.
On 6 October 2012, the remains of a frigatebird were recovered at João Barrosa beach (16°01.387’N, 022°43.610’W), southeastern Boavista, Cape Verde Islands. The carcass had been found in mid September 2012, during a beach survey to monitor loggerhead turtle nesting activity in the area and was then buried in the sand. The field assistant of the Cabo Verde Natura 2000 turtle project who found the bird indicated the location of the corpse to the first author. His description of the bird allowed it to be identified as an adult female magnificent frigatebird Fregata magnificens Mathews, 1914. The remains consisted of numerous black and white feathers as well as several bones, including the skull, thorax and wing bones, which are preserved at the Cabo Verde Natura 2000 headquarters at Sal Rei, Boavista. Some feathers, together with remains of an egg and tissue of a mummified male found at Ilhéu de Baluarte in 2005 (see below), were deposited at the Centro de Análise Molecular, Centro de Investigação em Biodiversidade e Recursos Genéticos (CMA/CIBIO), Vairão, Portugal.
On 10 February 2012, at 0845 UTC, a mass stranding involving seven (six adults and a juvenile) pygmy killer whales Feresa attenuata Gray, 1874 occurred at Praia de Boa Esperança (16º12’26”N, 22º52’00”W), along the northern coast of Boavista island, Cape Verde Islands. The event was witnessed by a group of kite-surfers, who managed to move three animals (two adults and a juvenile) back to the sea. No re-strandings were noted. At 1330 UTC, staff of the Protected Areas Department visited the site and recorded four specimens (two alive and two dead). At 1700 UTC, only two carcasses were found on the beach, the others apparently having been washed out to sea.
In the North Atlantic, the waters surrounding the Cape Verde Islands are a "potential hot spot" for cookiecutter shark Isistius spp. interactions with cetaceans. These occurrences were recently identified by the improved efforts of researchers to document cetacean strandings in the Cape Verde archipelago, as well as by the photo identification efforts of live whales and dolphins. The documentation of individual and mass stranding events confirmed that cookiecutter shark interactions with cetaceans in Cape Verde seas are remarkably common.
Humpback whales Megaptera novaeangliae perform the longest known migrations among mammalian species (Stone et al. 1990, Rasmussen et al. 2007), feeding at high latitudes during the summer and undertaking annual journeys to their wintering breeding grounds in warm and shallow tropical waters (Winn & Reichley 1985, Clapham & Mead 1999). Due to breeding site fidelity and temporal separation at low latitudes, gene flow between Northern and Southern Hemisphere populations appears to be very limited (Rizzo & Schulte 2009). However, inter-oceanic exchange has recently been documented (Pomilla & Rosenbaum 2005, Stevick et al. 2010), demonstrating that philopatry may not be as strong as previously inferred (cf. Baker et al. 1993, 1994, Valsecchi et al. 1997).
The abundance of humpback whales occurring around Boa Vista, Cape Verde Islands, was estimated by markrecapture modelling. Photographs of markings on tail flukes of individual whales were collected during the breeding season. Sighting histories were constructed for each individual and an abundance of 171 animals was estimated using a Jolly-Seber mark-recapture model. Correcting for known biases arising due to sex-specific behaviour and temporary emigration insofar as possible, an estimate of 260 whales was obtained. This is significantly higher than the previous estimate of 99 humpback whales from this region. Due to limited survey effort it is not known how representative the study area is of the entire Cape Verde archipelago and this estimate may be considered to be biased low and serves as a minimum estimate. The high recapture probability (0.37) coupled with the low abundance is consistent with a small local population. The low survival rate (0.86) suggests possible emigration and further studies are needed to assess connectivity between humpback whales breeding in Cape Verde and other breeding locations. The amount of exchange between groups of whales breeding in Cape Verde and adjacent areas remains unknown. It is unclear whether the abundance estimate herein applies to part of an isolated population or part of a larger and continuous one.
During August-September 2014 and 2015, yachtbased surveys were conducted in the Cape Verde archipelago with the main objective of trying to locate humpback whales Megaptera novaeangliae during the late boreal summer (Berrow et al. 2014). Spring breeding humpbacks in Cape Verde waters are known to have their feeding grounds in the high Arctic (e.g. Wenzel et al. 2009). While these animals have generally left the breeding grounds by mid-May, a number of sightings during the summer months (June- August) have raised the possibility that animals from southern stocks may occasionally reach as far north as Cape Verde (Hazevoet et al. 2011).
Gervais’ beaked whale Mesoplodon europaeus (Gervais, 1855) is restricted to the Atlantic Ocean. Although most records are from the North Atlantic, it is probably continuously distributed in deep warm waters around the equator (Mead 1989, Norman & Mead 2001). Its occurrence in West Africa is poorly known, as records are rare. It is classified as Data Deficient (Taylor et al. 2008).