Reproductive seasonality and trend of Chelonia mydas in the SW Indian Ocean: a 20 yr study based on track counts

Abstract

The green turtle Chelonia mydas is classified as endangered because of global declines over the past few centuries due to human exploitation and habitat destruction, particularly the loss of nesting areas. We used the number of tracks as an indicator of breeding female abundance at their nesting sites to study the seasonality and trends of turtles breeding at 3 islands in the SW Indian Ocean: Europa, Tromelin and Grande Glorieuse, over 20 yr. On Tromelin, tracks were counted along the entire nesting beach, but on Europa and Grande Glorieuse counts were limited to a proportion of the island. Europa and Tromelin exhibited similar seasonal patterns, with a well-defined peak during the wet season (November-February), compared to a dry season peak for Grande Glorieuse (March-June). The main season was significantly longer on Grande Glorieuse (288 ± 43 d) than on Europa (218 ± 60 d), with Tromelin intermediate (252 ± 43 d). There was greater variation in the start of a season compared to the median and end at all sites throughout the study. Approximately 7178 ± 3053 (n = 19) tracks were recorded annually on the entire nesting beach on Tromelin, compared with 1480 ± 666 (n = 19) on 16% of nesting beaches on Grande Glorieuse and 1361 ± 903 (n = 23) on 26% of beaches on Europa. The number of tracks has increased significantly on Europa (3% yr -1 ) and Grande Glorieuse (6% yr -1 ). The increasing number of nesting turtles illustrates the effectiveness of conservation measures on sites formerly exploited by humans.

Seasonality, abundance, and fifteen-year trend in green turtle nesting activity at Itsamia, Moheli, Comoros

“…locally weighted scatterplots smoothing). For comparison, classic seasonal decomposition of time series by loess (Cleveland et al 1990) has been used to investigate marine turtle nesting trends (Chaloupka 2001, Lauret-Stepler et al 2007 and was also applied to our data set, yielding results similar to the GAMM analysis (see Fig. S1 in the Supplement, available at www.int-res.com/articles/ suppl/ n027p265_supp.pdf, for details).…”

“…2 & 3); nonetheless, as at other nesting colonies, both regionally and worldwide (Bjorndal et al 1999, Cha loupka 2001, 2003, Bourjea et al 2007a, Lauret-Stepler et al 2007), they exhibit a distinct seasonal peak in nesting activity as well as strong variation in the total number of nesting attempts from year to year, a phenomenon that is usual and often documented in studies of green turtle nesting (see review for the western Indian Ocean in Dalleau et al 2012). Such seasonal variation could be due to environmental stochasticity at foraging grounds and the relatively low position of the green turtle in the food chain , Chaloupka et al 2008b).…”

“…Track counts, routinely used to estimate nesting abundance (Schroeder & Murphy 1999), were then calculated from daily observations, following the same protocols described in Lauret-Stepler et al (2007) and Bourjea et al (2007a). As not all nesting attempts result in successful nestings (i.e.…”

“…Nonetheless, the SWIO has hosted some of the world's most important nesting and feeding grounds for green turtles (Frazier 1971, 1975, 1984, Hughes 1973, Le Gall et al 1986, Le Gall 1988. This region, defined here as the waters bounded by the eastern coast of Africa extending from Kenya to South Africa and east as far as 60º E, nowadays includes major green turtle nesting areas such as Europa and Tromelin Islands (Lauret-Stepler et al 2007), Aldabra Atoll (Frazier 1971, 1984, Mortimer 1985, Mortimer et al 2011a, and Mayotte (Bourjea et al 2007a), where each island/atoll regularly hosts thousands of annual nesters. Wallace et al (2011) identified a single regio nal management unit for green turtles in the SWIO, and recent genetic research showed that this region hosts at least 3 different genetic management units for this species (Bourjea et al 2007b, in press).…”

Short Communication: Intertidal Rock Pool Fishes in the Natural Reserve of Glorieuses Islands (Western Indian Ocean)

“…These islands are classified as natural reserves since 1975 (Le Corre & Safford, 2001). Very few studies have been done on marine invertebrates (Gravier-Bonnet & Bourmaud, 2004;Vergonzanne, 1977), on turtles (Lauret-Stepler et al, 2007) and on the beach dynamics (unpublished data, Troadec, 1996). More recently, a coral fish inventory of this archipelago took place between 0 and 15 m depth using an underwater visual census .…”