Seasonality of Green Turtle (Chelonia mydas) Reproduction at Aldabra Atoll, Seychelles (1980-2011) in the Regional Context of the Western Indian Ocean

摘要

Seasonal and temporal-spatial distributions of green turtle {Chelonia mydas) nesting activity were assessed at Aldabra Atoll Seychelles, the second largest green turtle rookery in the Western Indian Ocean (WIO), based on morning counts of fresh turtle tracks conducted during 1980-2011. The datasets used in the analyses are derived from an average of 3-4 surveys per month at two index sites representing ～30%-42% of total annual nesting during 1980-1989 and ～58% during 1995-2011; and monthly surveys conducted at another two remote sites, which accounted for an additional 20% of annual nesting (total ～78%) during 2002-2011. Turtles engaged in year-round nesting during the season defined as December to November and characterized by patterns of high intra- and interannual variation. In some seasons, nesting peaked primarily during February to May, and in others during May to September, but on average during 1995-2011, a clear unimodal pattern emerged with nesting activity greatest during February to September, peaking during April to June, and lowest in November-December. The two Primary Index Sites situated 2.2 km apart on the west coast and separated by a lagoon entrance had mean peak nesting dates that consistently differed by more than a month. Possible explanations for the differences are discussed. At Aldabra, the timing of the 1997-1998 ENSO event coincided with a disruption in normal nesting cycles during 1998 through 2002 and the highest levels of nesting recorded at Aldabra to date during the 2000-2001 season. Comparison of seasonal median peak nesting dates at five green turtle rookeries in the WIO suggests an inverse relationship with latitude among four of them, with those in the lower latitudes peaking during the austral autumn and winter and in the higher latitudes during the austral summer, an indication that temperature may be moderating nesting seasonality in the WIO.