HEWITT DOLPHINS' REACTION TO A SURVEY VESSEL 



Table 3. — Average dolphin school composition. 



'Unidentified dolphins distributed proportionately among identified 

 dolphins following Holt and Pow/ers (1982). 



generously gave their time and advice during the 

 design of the experiment; and the conscientious 

 and competent field observers included G. Fried- 

 richsen in the helicopter, A. Jackson, W. Irwin, and 

 M. Noel on the NOAA ship Surveyor, and J. Cotton, 

 J. Doxey, M. Henry, M. Graybill, R. Pitman, and 

 G. Yee lead by W. Parks on the NOAA Ship David 

 Starr Jordan. R. Holt, T. Jackson, W. Perrin, and 

 P Vergne reviewed the manuscript. The final draft 

 benefited from the comments of two anonymous 

 reviewers. 



movement or visibility effects, will introduce a 

 negative bias in the density estimate that is pro- 

 portional to the decrease in apparent density 

 along the transect line (Smith 1979). The sample 

 size was insufficient to test this assumption rigor- 

 ously; only one school was observed on the transect 

 line (school 14) and it was detected well beyond any 

 of the reaction distances observed. 



It is recommended that future fieldwork include 

 additional comparisons of estimates of school size 

 and species proportions. In addition, the assump- 

 tion of certain detection along the transect line 

 should be tested. Biases in school composition and 

 detection on the transect line affect the abundance 

 estimates directly and present a greater potential 

 for inaccuracy than the degree of directed move- 

 ment prior to detection observed during this 

 experiment. 



ACKNOWLEDGMENTS 



This work was accomplished with the help and 

 collaboration of several people: D. Au, D. Chap- 

 man, P Hammond, J. Laake, and W. Perryman 



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HOLT, R. S. 



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