BARHAM ET AL.: AERIAL CENSl'S I1F THE BOTTLENOSE DOLPHIN 



d = 



2L(Y — 0.05) 



(14) 



where d = estimated dolphin density, 



n = total number of dolphin sightings, 

 L = length of the track line in km, 

 Y = mean perpendicular sighting distance 

 (minus the 50 m gap). 



These calculations gave a density estimate for 

 herds of 0.28/km^ compared with 0.095 for the 

 strip transect method (Table 2), evidence that the 

 latter method may have underestimated the dol- 

 phin density by about a factor of 3. 



In conclusion, the relatively few sightings in the 

 0-50 m perpendicular distance interval and the 

 exponential decrease in sightings at ranges > 100 

 m, strongly indicate violation of the strip transect 

 assumption that all herds within the delineated 

 strip were noted. If this is true then the population 

 has been underestimated to some degree, al- 

 though the inclusion of transects 1 and 2 would 

 tend to compensate for this. Conversely, one as- 

 sumption of line transect theory is that the targets 

 are randomly distributed. We found, however, 

 that the distribution of the dolphin herds was 

 strongly nonrandom. This factor may have caused 

 an upward bias to those calculations, but the pre- 

 cise impact of this violation is presently unclear. 

 These questions cannot be resolved until further 

 surveys are done simultaneously with adequate 

 "gi'ound truth" counts. 



ACKNOWLEDGMENTS 



This study was a collaborative effort among or- 

 ganizations within the NOAA's National Marine 

 Fisheries Service, the Marine Mammal Commis- 

 sion, Dinnes Memorial Veterinary Hospital, Sea 

 Arama Marineland of Galveston, and the Naval 

 Ocean Systems Center. We thank the adminis- 

 trators of these organizations for expediting the 

 work. We are also indebted to James McGrew for 

 his excellent piloting and Terrance Quinn II for 

 his suggestions. Gary Stauffer advised on statisti- 

 cal matters; the art work was done by Kenneth 

 Raymond and typing by Lorraine Prescott, all of 

 the Southwest Fisheries Center. The originally 

 submitted draft of this paper was read by William 

 Fox, Joseph Powers, and Nancy Lo of the South- 

 west Fisheries Center and Pat Tomlinson of the 

 Inter-American Tropical Tuna Commission. Fol- 

 lowing editorial review, Tim Smith of the South- 



we.st Fisheries Center consulted with the senioi' 

 author on additional statistical work in response 

 to suggestions by the referees. We also thank Lee 

 Eberhardt of Battelle Pacific Northwest 

 Laboratories as well as an anonymous reviewer 

 and the editor for their constructive comments and 

 suggestions. Despite the many contributions from 

 the junior authors, advisors, and reviewers, the 

 senior author, of course, assumes full responsibil- 

 ity for the contents of this paper. 



LITERATURE CITED 



Caldwell, D. K. 



1955. Evidence of home range of an Atlantic bottlenose 

 dolphin. J. Mammal. 36:.304-305. 



Eberhardt. L. L. 



1978. Transect methods for population studies. J Wildl 

 Manage, 42:1-31. 



ELLH)TT, J, M. 



1971 . Some methods for the statistical analysis of samples 

 of benthic mvertebrates. Freshwater Biol. Assoc, Sci. 

 Publ. 25, 144 p. 



Gates, C. E., W. H. Marshall, and D. P. Olson. 



1968. Line transect method of estimating grouse popula- 

 tion densities. Biometrics 24:135-145. 



Goodman, L. a. 



1960. On the exact variance of products. J. Am, Stat 

 Assoc, 55:708-713. 

 GL'NTER, G. 



1954. Mammals of the Gulf of Me.\ico, U,S, Fish Wildl 

 Serv., Fish, Bull. 55:543-551. 

 LE.-^THERWOOD, S. 



1975. Some observations of feeding behavior of bottle- 

 nosed dolphins ^Tiirsiops truncatus I in the northern Gull 

 of Mexico and ( Tursiops cf T. gilli ) off southern California, 

 Baja Cahfornia, and Nayant, Mexico Mar. Fish. Rev. 

 37(91:10-16. 



1979. Aerial survey of populations of the bottlenosed dol- 

 phin, Tursiops truncatus . and the West Indian manatee. 

 Tnchechus manatus, in the Indian and Banana Rivers. 

 Florida, Fish, Bull., U.S. 77:47-59, 



Leatherwood. S,, J, R, Gilbert, and D, G. Chapman, 



1978. An evaluation of some techniques for aerial censuses 

 of bottlenosed dolphins, J, Wildl, Manage, 42:239-250. 

 ODELL, D. K. 



1975, Status and aspects of the life history of tht 

 bottlenose dolphin, Tursiops truncatus, in Florida, J 

 Fish. Res, Board Can. 32:1055-1058, 

 SEBER, G. a. F. 



1973. The estimation of animal abundance and related 

 parameters. Charles Griffin, Lond., 499 p. 



SHANE, S. H. 



1977. The population biology of the Atlantic bottlenose 

 dolphin, Tursiops truncatus, in the Aransas Pass area of 

 Texas. M.S. Thesis, Texas A&M Univ.. 238 p. 

 ToWNSEND, C. H, 



1914. The porpoise in captivity, Zoologica (N,Y,) 1:289- 

 299. 

 Zak, J, H, 



1974, Biostatistical analysis. Prentice-Hall, Inc., En 

 glewood Cliffs. N.J. ,620 p. 



595 



