inaccessible nesting beaches. Aerial surveys also appear to be 

 the most cost effective method of conducting surveys of extensive 

 areas (>100 km) . As the flight frequency increases, a 

 documentation of important nesting beaches becomes more complete, 

 and we eventually obtain a relative distribution of nesting. If 

 flights are conducted frequently enough to correct for daily and 

 seasonal fluctuations in daily nesting effort, we can calculate 

 an index to the population which may be used to make comparisons 

 of population trends. These comparisons are frequently used as 

 three-year averages depending on the remigration interval. 

 Quantification of survey samples, information on daily nesting 

 effort for an entire season, and documentation of the number of 

 nests per female per year will allow the calculation of estimates 

 of numbers of nesting females. 



To determine the number of nesting turtles during the 

 previous night, the age of tracks is required. Attempts at 

 calculating mean age of a track seen from the air is futile as it 

 varies dramatically from day to day and between areas. In 

 addition, the visibility of old tracks seen from the air varies 

 considerably depending on light conditions, beach substrate and 

 track concentrations. The ability of aerial observers to 

 correctly count only fresh tracks (<24 hrs old) based on track 

 appearance has been consistently shown to be inadequate when 

 subjected to ground verification. With little wind and no rain, 

 fresh tracks are frequently difficult to discern from old tracks 

 when on the ground much less from the air. To resolve the 

 problem of aging fresh tracks correctly, we conduct our aerial 

 beach surveys on a specific tidal cycle. We fly at first light 

 on the morning after the high tide occurs around 2130 hrs. Thus 

 all lower portions (below mean high water) of old tracks have 

 been erased by the tide and all turtles nesting that night will 

 leave tracks between the high tide line and the waterline. Only 

 tracks in this intertidal zone are counted as fresh, and thus 

 during each flight only one 24 hr interval of nesting is 

 monitored. Using this tidal cycle, we could conduct three 

 surveys every two weeks of the season. This tidal technique 

 results in a less than 3% error in the aging of turtle tracks. 



Once the flight sample is quantified as to the days 

 surveyed, the daily distribution of nesting will allow estimates 

 of total nesting effort to be calculated. This may be obtained 

 from nesting records which are available from one or more areas 

 where daily ground surveys are conducted. These islands or 

 beaches must be an adequate sample of the total survey area for 

 the extrapolation to be reasonable. In place of single areas or 

 single years of ground truth, which may be much more variable 

 than the daily fluctuations of the extensive aerial survey areas, 

 we have combined daily nesting records for all areas and all 

 years to construct a composite nesting curve which does not show 



224 



