High-Density Loggerhead Sea Turtle Nesting on Dirk Hartog Island, Western Australia


The Western Australian population of loggerhead turtles, Caretta caretta, is recognized as a single genetic stock (Dutton et al. 2002; FitzSimmons et al. 1996; Limpus 2008). Nesting spans approximately 520 km from Steep Point (southwest of Denham) to the Muiron Islands (northeast of Exmouth) (Baldwin et al. 2003). Dirk Hartog Island is close to the southern end of this range. Nesting loggerheads have been flipper-tagged on Dirk Hartog Island nearly every year since 1993/94 (the 1994/95, 1995/96 and 2006/07 seasons were missed) as part of a mark-recapture program started by the Western Australian Marine Turtle Project, which is part of the Department of Parks and Wildlife (WAMTP, DPaW) (Prince 1994, 2000). Each year the number of peak-season nesting females tagged is counted, but a reliable estimate requires next-day track counts to account for those individuals missed during night surveys. In addition, spatial and temporal tagging effort has differed between years. Although tagged nesting females have been counted, morning surveys have not been conducted. Thus, mark-recapture data was the only way annual nesting numbers could be consistently quantified. The most recently published annual nesting population estimate for Dirk Hartog Island was approximately 1,000 or more individuals, based on late 1990s mark-recapture sample data (Baldwin et al. 2003). However, during some years with trained teams patrolling all beaches (1998, 1999, 2000, 2008) 1,400 turtles were tagged during each two-week peak period alone (WAMTP unpublished data), indicating annual nesting numbers greater than previously estimated. Remote area logistics constrain the tagging effort to two weeks each season. This pilot study used an alternative approach to estimating the numbers of loggerheads nesting at the peak of each season by using counts of turtle tracks and nesting success. Until a more recent mark-recapture analysis is conducted, this method allows repeatable counts of peak nesting numbers to be compared yearly. This is the first application of track count and nesting success methodology to the Dirk Hartog Island loggerhead sea turtle rookery.

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Author(s)Reinhold L
Whiting A
Published Date2014
Publication LanguageEnglish
CMS InstrumentIOSEA Marine Turtles