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154 B.J. Godley et al. / Biological Conservation 97 (2001) 151±158 nesting success was 99.5 (S.D.= 122; range= 5±444) while the mean number of surveys to collect these data was 14.4 (S.D.= 7.5; range= 10±37). The mean values for nesting success for each beach varied 4-fold, from 0.13 on beach 10 to 0.52 on beach 12 (Table 1), with a mean of 0.33 for all beaches (S.D.= 0.08; n=25 beaches). The overall nesting success for Ascension Island calculated as total nests divided by total activities was 0.39. When nesting success for the three main beaches (1, 12, 27) were plotted against time, no trends were detected. By multiplying the nest success (p) for each beach by the respective number of activities (a), the number of nests on Ascension Island over the season was estimated at 13,881. The fate of a nesting activity is e€ectively a binomial problem, with outcomes of either a ``nest'' or ``no nest''. We used a standard equation to calculate the variance in the estimate of the mean nesting success value for each beach, i.e. variance=pq/a where q=1 p (Bailey, 1981), and then from this variance 95% con- ®dence limits (95% CL) were determined. Since the variance of the sum of a series of estimates is simply the sum of their individual variances, the 95% con®dence limits on the estimate for the total number of nests was readily determined as 13,092±14,660. 3.2. Magnitude of nesting A total of 36,036 marine turtle nesting activities was estimated over the entire season, with the number of activities per beach ranging from 47 to 9651. Density of nesting activities varied widely from 534 to 10,001 activities/km, as did nest density which ranged from 213 to 5200 nests/km. Overall density of activities (total activities/total beach surveyed) was 6204 activities/km and total nest density (total nests/total beach surveyed) was 2390 nests/km. 3.3. Spatial distribution of nesting e€ort Included for comparison are data from the surveys by Mortimer and Carr (1987; Table 2), and Mortimer (1992; from a partial survey carried out in April 1992). There were many more activities in the 1998/1999 season than in the two seasons recorded by Mortimer and Carr (1987), with the total being greater by an order of two and three than in 1976/1977 and 1977/1978 seasons, respectively. To compare the spatial variation in nesting e€ort of the 1998/1999 season with that of previous surveys (Mortimer and Carr, 1987; Mortimer, 1992), data from individual beaches were combined into the clusters de®ned by Mortimer and Carr (1987; Table 1). In general, among beach spatial variation was similar in all seasons. The only marked change since the studies in 1976±1978 appears to be the proportion of nesting occurring on beach number 12. 3.4. Temporal distribution of nesting e€ort The temporal distribution of nesting activities is shown in Fig. 2. Nests were ®rst recorded on 2 December 1998 and continued until the last clutch was laid on 31 August, 1999. The peak of nesting was in March with 90% of nesting occurring between 13 January and 7 May 1999 and 95% of nesting recorded between 4 January and 18 May 1999. We used stepwise multiple regression to investigate the relationship between the available weather parameters (maximum temperature ( C), minimum temperature ( C), rainfall (mm)) recorded on each day (2 December 1998 to 31 August 1999) and the estimated number of nests for that day on the whole island. The most signi®cant variable was maximum daily temperature (r 2 =0.58) with a model including temperature and rainfall explaining slightly more of the variance Table 2 Estimated number of activities recorded in the 1998/1999 season in comparison with data collected by Mortimer and Carr (1987) in the 1976/1977 and 1977/1978 seasons. In addition, data from the partial survey carried out by Mortimer (1992) are included Beaches 1976/1977 1977/1978 1991/1992 1998/1999 c 1 2793 (15.4) a 2195 (18.2) (13.1) 4500 (12.5) 2±5 1821 (10.0) 1569 (13.0) (11.3) 5434 (15.1) 6±11 2453 (13.5) 1428 (11.8) (17.0) 4599 (12.8) 12 3118 (17.1) 1760 (14.6) (28.1) 9651 (26.8) 14±20 1341 (7.4) 783 (6.5) (1.4) 2819 (7.8) 21±26 976 (5.4) 822 (6.8) (5.5) 1820 (5.1) 27 2703 (14.9) 1469 (12.1) (12.5) 3216 (8.9) 28 804 (4.4) 420 (3.5) (1.8) 1172 (3.2) 29 1743 (9.6) 1191 (9.8) (6.9) 1986 (5.5) 30±32 440 (2.4) 456 (3.8) (2.6) 839 (2.3) Total 18,192 12,093 na b 36,036 a Numbers in parentheses denote the percentage of the total for the season. b na, Not applicable. c It should be noted that in 1998/1999, data were not included from beaches 13, 18, 19, 20 and 32 (see Section 2).
B.J. Godley et al. / Biological Conservation 97 (2001) 151±158 155 Fig. 2. Temporal distribution of nesting activities of green turtles on Ascension Island during the 1998/1999 season. For each beach, the number of nests was subsequently calculated by multiplying the actual or interpolated number of nesting activities for that day and the overall nesting success for the season on that beach. Fig. 4. Monthly mean sand temperature on beach 12 (January 1985± December 1997) predicted using the relationship between monthly mean maximum air temperature measured at the Ascension Island Air®eld and the sand temperature at nest depth on that beach (Hays et al., 1999). (r 2 =0.59). Overall, as air temperature increased so did the daily number of nests (Fig. 3). To investigate the possible e€ect of rainfall on nesting success, for each 10 day period, mean rainfall and mean nesting success were compared using regression analysis and no signi®cant relationship was found (F 1,15 =0.03, p=0.87, r 2 =0.02). The close link between air temperature and sand temperature at nest depth has previously been described for Ascension Island (Hays et al., 1999). This relationship (mean monthly sand temperature ( C) on Long Beach =1.6+0.908 mean monthly daily maximum temperature; F 1,10 =498, p
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