Loggerhead (Caretta caretta) and Leatherback (Dermochelys coriacea) nesting activity along the Maputaland coast (South Africa) : 1965 - 2002

From 1963 until the present, loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) female turtles nesting on a 56-km stretch of beach in Maputaland, on the northeast coast of KwaZulu-Natal, South Africa have been tagged and monitored. In this study, population trends, size, preference for timing of nesting and nesting sites, and seasonality in nesting activity and nesting area were analysed and the effectiveness and efficiency of the monitoring programme assessed. Since the programme's inception, approximately 46893 loggerhead and 11509 leatherback females have nested on the Maputaland beaches. A non-linear relationship was found between the numbers of nesting females of both species over time, with three distinct phases. large interannual variations in nesting numbers were evident for both species, as were synchronized seasons of elevated or depressed nesting activity. While Maputaland leatherbacks appear to be approximately the same size as in populations elsewhere, the loggerhead females were significantly smaller compared to other populations. Peak nesting activity occurred from November to January and was associated with warmer sea temperatures, as was the subsequent emergence of hatchlings. Marginal temporal shifts in the nesting numbers of both species were evident during peak nesting-activity seasons, with the peak nesting period beginning slightly earlier than usual. Peak nesting-activity seasons appeared to follow EI Nino events with a lag period of between 0 and 2 years. Separate 'preferred' nesting areas were found for each species, largely associated with the offshore seabed topography. The loggerheads exhibited a fairly narrow nesting-area distribution in the north, while the leatherbacks utilised a far wider area in the southern region. The length of the 'preferred' nesting area (km) was strongly correlated with the total number of nesting loggerhead and leatherback females. No major nesting-area shifts were evident over the programme's duration. However, distinct spatial shifts, with increases in the length of the 'preferred' nesting area, were evident for both species during peak nesting-activity seasons, and was possibly related to the increased influx of nesting females. Interspecific competition appeared to be of little importance in Maputaland, as both populations displayed strong synchrony in nesting declines and increases over time, and while both populations have increased, no major shifts in the 'preferred' nesting area of either species have occurred. No correlations were found between the Southern Oscillation Index (SOl) values and nesting activity or changes in nesting area. However, a negative correlation was found between the average curved carapace lengths (CCl) of both species and the SOl values, most likely related to sea surface temperatures and the resultant changes in food availability that occur during EI Nino events. Disturbance incurred during monitoring caused, at most, only a 5% reduction in the nesting rates of both species. To date, the conservation efforts of the monitoring programme appear to have come to fruition, with both the loggerhead and leatherback nesting populations healthy and in a more-or-Iess stable state. The importance and value of continuing the current monitoring programme was emphasized, and several management and sampling strategies proposed for future seasons.

Grantor dc:publisher.institution

Department of Oceanography

Year dc:date.issued

2004

Author dc:creator

• Wright, Ruth Vivienne

Advisors dc:contributor.advisor

• Nel, Roel
• Govender, Anesh
• Branch, George M

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/6442

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/6442