FISHERY BULLETIN: VOL. 8fi. NO. 4 



3.104 



> 



M 



Z 

 111 



o 

 >■ 



< 

 a 

 o 



DISTANCE FROM TRANSECT (km) 



Figure 4.— Four-term Hermite probability density function fit to histogram of bottle- 

 nose dolphin sighting frequency and perpendicular distance (rescaled to account for 

 the "blind spot" beneath the aircraft). Numbers above bars denote number of sight- 

 ings in interval. 



in the CBM (Table 3). CBM and coastal surveys were 

 flown sequentially with no delay between them and 

 the relatively high speed of the aircraft prevented 

 counting of the same herd twice. Therefore, the 

 abundance estimates in the CBM and the southern 

 coastal survey areas may be considered additive and 

 totaled 340 bottlenose dolphins (±104, 95% C.I.)- 

 The survey altitude limited observations of herd 

 composition to the percentage of calves in each herd. 

 Bottlenose dolphins much smaller than the others 

 and accompanied by a larger bottlenose dolphin 

 were considered to be calves. The mean percentage 



Table 3. — Summary of aerial survey results of bottlenose dolphins. 

 N is the number of surveys; L is the total length of transects at each 

 location in km; and n is the number of herd sightings within one 

 km of the transect. D is estimated herd density (herds/km^); P is 

 estimated dolphin density; and A is estimated dolphin abundance 

 (standard errors in parentheses). 



of calves in all herds from all study areas peaked 

 in June at 9.5% (SE = 0.8, n = 3) and declined 

 thereafter until September (Fig. 5); however, there 

 were no significant differences between months 

 (K-W test, r = 9.1930, df = 5, P > 0.10). Con- 

 sidering the total study period, the mean percentage 

 of calves in herds in the CBM area was 7.5% (SE 

 = 3.2%, n = 5); in the southern coastal area, 4.3% 

 (SE = 1.0%, n = 49); and in the northern coastal 

 area, 9.0% (SE = 1.8%, n = 2). The mean percent- 

 age of calves in herds did not differ significantly 

 among areas (K-W test, x" = 2.8196, df = 2, P = 

 0.24). 



Bottlenose dolphins were never sighted more than 

 1.6 km from shore during CBM surveys nor during 

 subsequent surveys up to 8 km offshore of the 

 coastal study area. Also, bottlenose dolphins were 

 not found in depths greater than 10 m except in the 

 Eastern Shore area. Plotting of bottlenose dolphin 

 sightings (Fig. 1) shows a uniform distribution along 

 the southern coastal area with some clusters of 

 sightings at Cape Henry and at Cape Charles. 



During 1980, seven bottlenose dolphins which 

 were recognizable by the shape of the trailing edge 

 of their dorsal fins were identified and photo- 

 graphed. In 1981, 17 individuals identified from 

 dorsal fin photographs included 5 which had been 

 photographed in 1980. Thus, of the 19 recognizable 



802 



