IRVINE ET AL.: MOVEMENTS AND ACTIVITIES OF ATLANTIC BOTTLENOSE DOLPHIN 



matic Direction Finder. The tags and marking 

 techniques used in the study were described and 

 evaluated by Irvine et al. (footnote 7). 



The boat used as a tagging platform and for 

 surveys and radio tracking was a 7.3 m Wellcraft 

 "Fisherman," equipped with a 3 m tuna tower. 

 During captures, the boat was camouflaged with 

 canvas and netting and towed to the capture site to 

 lessen chances that tagged bottlenose dolphins 

 might later recognize the motor sounds or visually 

 identify the boat, and avoid it during surveys. 



Radio-tagged bottlenose dolphins were usually 

 tracked continuously for 24-48 h after installation 

 of the radio transmitter and then relocated and 

 tracked intermittently during the remaining life 

 of the transmitter. As reported by Martin et al. 

 (1971), the radio tags transmitted only when 

 the antenna was at the surface, enabling us 

 to measure dive times by timing the intervals 

 between transmissions. Tracking was generally 

 conducted from a distance and at anchor, to lessen 

 possible influences of the tracking boat on 

 the bottlenose dolphins' movements. Locations of 

 radio tagged animals were determined at night by 

 triangulation and during the day by triangulation 

 or occasional sightings. 



Boat surveys were conducted during periods 

 when bottlenose dolphins were not being radio 

 tracked. Surveys were conducted at least twice a 

 week and were concentrated in northern inshore 

 areas (Figure 2). Surveys were extended to include 

 the Gulf of Mexico and southern inshore 

 areas when time was allowed. Survey routes were 

 influenced by tide and wind but were usually 

 confined to channels or other areas >1 m deep 

 (Figure 2). 



During boat surveys and tracking trips, all 

 dolphins sighted were counted, and tagged or 

 marked individuals were identified if possible. 

 Groups containing several recognizable animals 

 were usually observed for longer periods to verify 

 identities and associations. The distribution 

 of sightings was therefore influenced by boat 

 channels and by the length of time that groups 

 were followed. 



The location and direction of movement of all 

 bottlenose dolphins sighted were noted on charts, 

 and notes on each encounter were entered on data 

 sheets. To correct for repeated sightings of known 

 individuals during the same survey, we based 

 distribution and herd size analyses on sightings 

 more than 1 h apart. Associations between recog- 



nizable bottlenose dolphins were compiled as one 

 sighting per group per day, but were retabulated 

 each time the composition of a group changed. For 

 "seasonal" analysis, the year was divided into 

 quarters based on the beginning of field activities 

 (29 January 1975) as follows: February March, 

 and April (spring); May, June, and July (summer); 

 August, September, and October (fall); and 

 November, December, and January (winter). 



Population units were difficult to define be- 

 cause sea conditions and local topography usually 

 limited sightings to nearby animals. Conse- 

 quently, all bottlenose dolphins sighted within 

 about 100 m of the boat were defined as a 

 group. The smallest group of bottlenose dolphins 

 observed to be closely associating and engaging in 

 similar activities was labeled a primary group. 

 Combinations of primary groups were labeled 

 secondary groups. A "herd" was defined as an 

 aggregation of bottlenose dolphins that more 

 or less regularly occupied a given area and inter- 

 acted socially with each other to a markedly 

 greater extent than with bottlenose dolphins in 

 adjacent areas. This definition of a herd was based 

 on observed social interactions or associations 

 over an extended period of time. At any given 

 time, the members of the herd were distributed 

 among a number of primary and secondary 

 groups. Herds sighted during aerial surveys 

 (e.g., Leatherwood et al. 1978) have been defined, 

 by necessity, by proximity of animals sighted, and 

 are probably most comparable to our definitions of 

 primary and secondary groups. 



RESULTS AND DISCUSSION 



Forty-seven bottlenose dolphins (24 males, 23 

 females) were captured or recaptured for tagging 

 a total of 90 times between 29 January 1975 

 through 25 July 1976. Ten dolphins i designated 

 RT-1 to RT-10) were fitted with radio tags and 

 radio tracked for up to 22 d. The total of 3,331 

 bottlenose dolphins sighted (Figure 3) included 

 2,373 during surveys (730.2 h), 529 during radio 

 tracks (245.3 h), and 429 during capture efforts 

 (150.8 h). Of the 997 marked bottlenose dolphins 

 that were sighted, 781 were tagged and identifi- 

 able, 129 were tagged but unidentifiable, and 87 

 (distributed among 12 dolphins) were identifiable 

 by distinctive natural marks (usually dorsal fin 

 shape). Numerous sightings from close range 

 suggested that tagged bottlenose dolphins did not 

 attempt to avoid the tagging-observation boat. 



673 



