FISHERY BULLETIN VOL, 77, NO, 2 



Detailed work on the social organization of 

 bottlenose dolphins was carried out by Irvine et al. 

 (see footnote 2) and Wells et al. (in press). They 

 captured many animals for tagging, and thus 

 gained size and sex information. They found that a 

 resident herd in the Sarasota-Bradenton area of 

 West Florida consisted of groups whose individual 

 membership was constantly changing by influx 

 and efflux in a "kaleidoscopic manner." Such 

 changes were not random, however, and several 

 patterns of association were observed. Within a 

 relatively stable herd occupying a well defined 

 home range, each age and sex class frequented 

 particular regions and interacted with other 

 classes to varying degrees. Females of all ages and 

 adult males ranged through the northern portion 

 of the home range and interacted more with each 

 other than with subadult males, which formed 

 bachelor groups or groups with one or more adult 

 females in the southern portion. Females with 

 young moved throughout the home range and in- 

 teracted with adult males to a lesser extent than 

 did other females. A given group generally re- 

 mained intact for only a matter of hours or days. 



At least superficially similar group instability 

 was documented for Argentine bottlenose dol- 

 phins by Wiirsig and Wiirsig (1977) and Wiirsig 

 (1978), for Texas bottlenose dolphins by Shane 

 (1977), for Hawaiian spinner dolphins by Norris 

 and Dohl (see footnote 3), and for humpback dol- 

 phins by Saayman and Tayler (in press). These 

 studies present the first detailed accounts of some 

 aspects of social organization of odontocete ceta- 

 ceans, and make comparisons of these animals 

 with terrestrial mammals such as bovids and pri- 

 mates possible. 



The present analysis of South Atlantic bottle- 

 nose dolphins represents an attempt to describe 

 the general movement patterns, aerial and social 

 behavior, and ecology of this population. We made 

 no attempt to capture animals for sex and size 

 information as we were loathe to disturb their 

 "natural" movement and social behavior. Instead, 

 we observed them mainly from cliffs lining the 

 shore. Earlier, we reported on some aspects of sea- 

 sonal occurrence patterns, group stability, surfac- 

 ing associations, and calving seasonality of the 

 same population discussed here (Wiirsig and Wiir- 

 sig 1977; Wiirsig 1978). This paper presents addi- 

 tional information, with the primary purpose of 

 providing background data on the natural history 

 of bottlenose dolphins, and hopefully also with 



future application to other species as further 

 studies unfold. 



MATERIALS AND METHODS 



Bottlenose dolphins were observed at Golfo San 

 Jose ( lat. 42°23' S., long. 64°03 ' W.) from July 1974 

 through March 1976. We made observations 

 through binoculars and a 20-power transit 

 monocular from two points, 14 m and 46 m high at 

 mean low water ("Camp" and "Cliff Hut," respec- 

 tively. Figures 1, 2). 



To describe the movements of dolphin sub- 

 groups (averaging 15 animals) which were present 

 near the observation point anywhere from several 

 minutes to several hours, we plotted their posi- 

 tions with the help of a Kern= model DKMl sur- 

 veyor's theodolite. The theodolite had a 20-power 

 monocular through which the animals were fol- 

 lowed visually. A separate eyepiece showed hori- 

 zontal degrees and vertical degrees which rep- 

 resented the location of the dolphins, and which 

 we read at 15 s to several-minute intervals into a 

 cassette recorder. In the laboratory, data from the 

 theodolite were plotted on a depth map (Figure 2), 

 by a Hewlett-Packard Model 9830A desk cal- 

 culator and plotter. Besides plotting the animals' 

 positions, the computer program also supplied 

 their distance from the observer, their heading 

 in degrees relative to true north, and their 

 speed. 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service. NOAA. 



/?_^22122l5 



FIC.URE 1.— Map of Golfo San Jose on Peninsula Valdes. Argen- 

 tina, The bay is approximately 750 km^ with a 7 km wide mouth 

 opening to the Atlantic, The lined area in the southeast portion . 

 of the bay represents the study area. The crosshatched subsec- | 

 tion is shown m detail in Figure 2. • 



400 



