BARHAM ET AL AERIAL CENSUS OF THE BOTTLENOSE DOLPHIN 



sent about IV/f coverage of the survey area on any 

 one replicate. 



Dolphin Counts 



During the first four survey flights 133 dolphin 

 herds were sighted, containing an estimated 916 

 animals. A mean of 33.3 herd sightings per survey, 

 composing 229 dolphins, was calculated for the 

 four flights (Table 1). On survey 5, affected by 

 adverse weather, only 19 herds estimated to con- 

 tain 107 dolphins were sighted. Because these 

 scores fell well below two standard deviations of 

 the mean that was calculated for the first four 

 replicates (Table 1). the results of survey 5 were 

 excluded from our population calculations. Data 

 from the last survey were used, however, for 

 analyzing behavioral observations, sighting cues, 

 and the perpendicular distances of dolphin herds 

 from the trackline. 



T.ABLE 1. — Bottlenose dolphin herd sightings, individuals, and 

 calves estimated on surveys 1-4 Port Aransas to Matagorda. 

 Texas. 



on 



1 ; J 4 5 6 ^ e 3 10 (£ p? la 15 16 I - " ^^ 2j ^6" 35 



HERD SIZE 



FIGURE 4. — Frequency distribution of bottlenose dolphin herd 

 sizes on surveys 1-4, Port Aransas to Matagorda, Texas. 



The mean herd size for each daily survey repli- 

 cate was computed as: 



1=1 "; 



(1) 



where h , = mean herd size, 



hi, = herd size of the ith sighted herd 

 on replicate 7, 



rij = the number of herds sighted during 

 replicate J. 



The estimated herd density for each replicate 

 was obtained from: 



Dj = 



(2) 



'Tfie last four transects were run on Marcti 30 



Calves 



Among the animals sighted in surveys 1-4, some 

 8.5 were classified as calves, and they represented 

 9.3"f of the total population observed (Table 1). 

 Because the surveys were made just prior to the 

 peak of the calving season, it was not always pos- 

 sible to differentiate between older calves of the 

 year and young yearlings. Some 13 animals were 

 in this questionable category. 



Herd Size and Herd Density 



While the estimated sizes of herds ranged from 1 

 to 42 animals, generally the aggregations were 

 small. Groups of two and three T. truncatus rep- 

 resented the mode and composed 28.6% of all 

 sightings, and 96 of the 133 sightings (72.2% ) were 

 composed of 7 or less animals (Figure 4i. 



where D, = the estimated herd density on rep- 

 licate 7, 

 a = the surveyed area in km'^, 

 Hi = is defined as before. 



These calculations produced a mean herd size of 

 6.95 and a mean herd density of 0.0947/km^ (Table 

 2). 



Estimated Population Size 

 (Numbers of Dolphins) 



In previous aerial assessments of bottlenose 

 dolphin populations by Leatherwood and his co- 

 workers, variance of the population size was calcu- 

 lated according to Goodman's (1960) equation for 

 estimating the variance of a product of two inde- 

 pendent variables. However, in these cases Good- 

 man's equation was used to estimate variance of 

 the mean population size over all the replicates 



589 



