Gilpatrick Estimation of dolphin school size with aerial photography 



647 



225 



2.23 - 



222 - 



C 2 18 — 



2 16 — 



2 15 



Experimental time points 



Figure 3 



Temporal profiles of the means for counts I log-transformed I made by three 

 independent readers during the repeated-counts experiment. 



1991 counting period, a "warm-up" counting session 

 was effective in improving estimate precision, i.e, be- 

 tween-reader CV went from an average of 8% to 4% 

 within one day. 



Acknowledgments 



Thanks to N. Chyan-huei Lo of the South- 

 west Fisheries Science Center (SWFSC), 

 and to Boyd D. Collier of San Diego State 

 University for advice on analyses. M. S. 

 Lowry assisted with aerial photography. 

 Thanks to fellow members of the Photo- 

 grammetry and Remote Sensing Group 

 at the SWFSC: W. L. Perryman, R. L. 

 Westlake, and M. S. Lynn. Figures and 

 tables were drafted by R. M. Allen, H. M. 

 Orr, and K. Raymond. T Gerrodette re- 

 viewed an earlier version of the manu- 

 script. This report was improved by com- 

 ments of W. L. Perryman, C. A. M. 

 Salvado', D. P. DeMaster, A. E. Dizon, 

 M. D. Scott, J. Barlow, S. B. Reilly, 

 W. F. Perrin, and three anonymous re- 

 viewers. C. Blair edited the manuscript. 

 Aerial photography at sea was accom- 

 plished with the cooperation of the 

 captain, officers, and crew of the NOAA 

 ship David Starr Jordan and the pilots 

 of NOAAs Aircraft Operations Center (AOC). 



Literature cited 



Conclusion 



Results suggest that after a prolonged absence from 

 interpreting dolphin school photographs and doing 

 counts, a warm-up session, where readers are refreshed 

 in counting technique, is important for minimizing 

 reader error and improving precision. Estimate pre- 

 cision is also improved when plotting and counting is 

 initiated at the dolphin high-density area in a photo- 

 pass. The field and laboratory methods described in 

 this report proved reliable in providing precise dol- 

 phin school-size estimates for population abundance 

 studies. The CV statistic and PD index will be used for 

 inter- and intra-annual quality control of dolphin school 

 estimates taken from aerial photographs. The ana- 

 lytical methods used in this paper to describe preci- 

 sion and consistency are applicable to other fisheries 

 and terrestrial wildlife research efforts where inde- 

 pendent repetitive counts are conducted for parameter 

 estimation. 



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