Occurrences des observations de la campagne REMMOA Guyane (2008)

Study Extent

In Guiana, the French EEZ (4–9°N, 49–54°W), spanning 132,000 km2, extends 200NM into the Atlantic Ocean, including a broad continental shelf, a slope, wider on its western part and an abyssal plain where depths approach 4500 m. The French EEZ in the Antilles (14–19°N, 57–64°W), spanning 143,000 km2, extends from Guadeloupe and Martinique Islands, 200NM into the Atlantic Ocean and 80NM into the Caribbean Sea and northward around St Barthélemy and St Martin islands.

Sampling

Aerial surveys were based on standard line transect sampling (Buckland et al., 2001). Transects were sampled at a target altitude of 182 m (600 ft) and a ground speed of 90 knots (167 km·h−1). Survey platform was a Partenavia P68, a high-wing, double-engine aircraft equipped with bubble windows so that observers could scan right underneath the plane. Survey crew consisted in two trained observers observing with naked eyes and a flight leader in charge of data collection on a laptop computer. A GPS, logged to a computer equipped with ‘VOR’ software (designed for the aerial survey of the SCANS-II program Hammond et al., 2006), collected positional information every 2 s. Additionally, Beaufort Sea state, turbidity, glare, cloud coverage as well as an overall subjective assessment of sighting conditions were collected at the beginning of each track line and whenever any of these values changed. The general protocol corresponded to published protocols prepared for small cetaceans (e.g. SCANS programs, Hammond et al., 2002, 2006). In addition to this, presence and group size of larger cetaceans, seabirds, sea turtles and elasmobranches were collected as well. Information recorded included identification to the taxonomic level, group size and angle to the track line, measured with a hand-held clinometer. Together with the altitude of the aircraft, the angle provided the perpendicular distance of the animal from the track line, which allowed distance sampling analyses to be conducted (Buckland et al., 2001). However, for seabirds, data was collected using the strip transect methodology based on the assumption that all seabirds within the strip are detected (Eberhardt 1978; Tasker et al. 1984). This methodology was used in an attempt to avoid disrupting the attention of the observers from the target species (cetaceans) in areas of high seabird densities. Strip width was 500 m on both sides of the track line in the Antilles and 150 m in Guiana. Identification was made to the lowest taxonomic level whenever possible, but groupings were inevitable for animals that could not be told apart from the air. Brown terns and brown boobies are examples of such groupings in the Antilles

Method steps

1. Les données d’observation, ainsi que l’effort et les conditions d’observation sont transférées dans une base de données sous MS Access 2000 après validation par les observateurs. Les cartes et les pré-analyses de distribution ont été réalisées avec le logiciel ArcGis 9.2 et son extension Spatial Analyst. Les données sont ensuite analysées sous le logiciel libre R pour la construction des modèles spatiaux.

In Guiana, the French EEZ (4–9°N, 49–54°W), spanning 132,000 km2, extends 200NM into the Atlantic Ocean, including a broad continental shelf, a slope, wider on its western part and an abyssal plain where depths approach 4500 m. The French EEZ in the Antilles (14–19°N, 57–64°W), spanning 143,000 km2, extends from Guadeloupe and Martinique Islands, 200NM into the Atlantic Ocean and 80NM into the Caribbean Sea and northward around St Barthélemy and St Martin islands.