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Field Diary Nest stats G Loggerhead
Field Diary Nest stats G Loggerhead

Nest statistics 2010/11

Monitoring work at Gnaraloo drew to an early close on 7 February 2011, with significantly reduced turtle beach activities being observed in the study area. GTCP researchers left Gnaraloo shortly thereafter to travel to Geraldton to undertake data analysis and report writing under the guidance and supervision of the program’s project manager, Karen Hattingh.

During the nesting season 2010/11, a total of 799 turtle activities (comprising of 426 nests and 373 unsuccessful nesting attempts) were recorded in the study area (~7 km) during the monitoring period of 87 days.  An unsuccessful nesting attempt is where a turtle starts clearing an area or digging an egg chamber, but does not complete the process and returns to sea without depositing eggs.

Results showed Loggerheads as the dominant species using the rookery, with 402 nests.  The area was also used by Green (8 nests) and Hawksbill nesting females (2 nests).  It is estimated that there was between 80 – 134 nesting Loggerhead females in the study area during 2010/11.

Night checks were carried out by GTCP researchers for part periods during 19 November 2010 – 18 January 2011 in order to determine the margin of error in predictive species identification through track monitoring during morning patrols.  In terms of species identification, 96.5% of results positively correlated between the night surveys and morning track monitoring.  The misidentifications occurred during the first month of monitoring.  After 1 month of frequent night checks and daily morning patrols, species identification by GTCP researchers reached 100% accuracy and correlation.

These results confirm the accuracy and integrity of the GTCP species identification data 2010/11 and demonstrate that several weeks of track monitoring are essential in order for trackers to become 100% efficient and reliable in terms of species identification.

In terms of nest activity determination (the identification of nests versus unsuccessful nesting attempts), 89% of results positively correlated between the night checks and the morning track patrols.  Errors related to nests mistaken for unsuccessful nesting attempts.  The margin of error was due to the lack of experience of the GTCP researchers in nest identification (especially at the start of the nesting season) and by a wide variety of environmental conditions impacting the tracks as well as nest data collection.  Becoming 100% efficient in terms of Loggerhead nest identification is hard to achieve even after many years of experience!  Future GTCP researchers will need to consider as many clues as possible in order to reduce the margin of error in determining of nest activity type.

These results on nest activity determination mean that the number of nests in the Gnaraloo Bay Rookery has probably been under-estimated since 2008 which makes the Gnaraloo breeding area even more important than thought before!
We’ll let you know more soon,

The Turtles and Mama

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