OCCURRENCE, MOVEMENTS, AND DISTRIBUTION OF 

 BOTTLENOSE DOLPHIN, TURSIOPS TRUNCATUS, IN SOUTHERN TEXAS 



Susan H. Shane* 



ABSTRACT 



Boat and land observations of free- ranging bottlenose dolphins, Tursiops truncatus, near Port Aransas, 

 Texas, provided data on seasonal occurrence, daily movements, and individual distribution patterns. 

 Censuses revealed that the winter population in the study area was twice the size of the summer 

 population. Individual dolphins were variously identified as summer residents, winter residents, or 

 year-round residents in the study area. There was a significant relationship between dolphin move- 

 ments and tide in some sections of the study area. Dolphins consistently moved against the ebb tide and 

 sometimes against the flood tide in these sections. Time of day was significantly related to dolphin 

 movements in a few sections of the study area. Part or all of the study area was included in the home 

 ranges of several individually recognizable dolphins. 



Only three long-term studies of free-ranging At- 

 lantic bottlenose dolphins, Tursiops truncatus, 

 have been conducted (Wiirsig and Wiirsig 1977, 

 1979; Hogan^; Irvine et al.^). Bottlenose dolphins 

 in Texas have been studied only opportunistically 

 by Gunter (1942, 1943, 1951). Lack of detailed in- 

 formation on free-ranging T. truncatus provided 

 an incentive for a 1-yr study of bottlenose dolphins 

 in southern Texas. This paper presents data on 

 seasonal occurrence, daily movements, and indi- 

 vidual distribution patterns of dolphins in the 

 study area. 



METHODS 



The study area was located near Port Aransas, 

 Texas, (lat. 27°50'15" N; long. 97°02'45" W) and 

 included seven sections (Figure 1). Aransas Pass is 

 the shipping outlet into the Gulf of Mexico for the 

 Port of Corpus Christi. The next open pass through 

 which dolphins could enter or leave the Gulf is 

 Cedar Bayou, a natural pass, located 37 km to the 

 northeast. Sections 1, 2, and 6 are dredged to a 



'Department of Wildlife and Fisheries Sciences, Texas A&M 

 University, College Station, TX 77843; present address: National 

 Fish and Wildlife Laboratory, 412 N.E. 16th Avenue, Gainesville, 

 FL 32601. 



''Hogan, T. 1975. Untitled draft of M.S. thesis. Unpubl. 

 manuscr, 42 p. Univ. Rhode Island, Kingston. 



^Irvine, A. B., M. D. Scott, R. S. Wells, J. H. Kaufmann, and W. 

 E. Evans. 1979. A study of the activities and movements of 

 the Atlantic bottlenosed dolphin, Tursiops truncatus, including 

 an evaluation of tagging techniques. Available National Tech- 

 nical Information Service, 5285 Port Royal Road, Springfield, VA 

 22151 as PB-298 042. 



depth of 14 m and are all used by large tankers and 

 a variety of other boats. Sections 3 and 7 are 

 dredged to a depth of 5 m and are used by commer- 

 cial and sport fishing boats, barges, and pleasure 

 boats. Sections 4 and 5 average 2-3 m deep and are 

 frequented only by small fishing boats. The entire 

 study area covers approximately 34 km^. 



Between 1 June 1976 and 31 May 1977, I spent 

 1,065 h observing dolphins, either from a 4 m Bos- 

 ton Whaler'* or from land. Opportunistic observa- 

 tions were made from June through December 

 1977. Uniquely marked dorsal fins (Wiirsig and 

 Wiirsig 1977) were used to identify 21 individual 

 dolphins, and these individuals provided informa- 

 tion on distribution and seasonal movements. 



I defined the seasons as follows: 1) summer, 

 June- August; 2) fall, September- November; 3) 

 winter, December-February; 4) spring, March- 

 May. Initially, air and water temperatures from 

 the U.S. Coast Guard Station at Port Aransas 

 were used, but after 1 December 1976 I collected 

 these data at the beginning of each day in a harbor 

 off Aransas Pass. Mean air and water tempera- 

 tures were 28.2° and 28.4° C for summer 1976, 18.7° 

 and 18.8° C for fall 1976, 1L2° and 1L4° C for winter 

 1976-77, and 22.5° and 22.7° C for spring 1977. 



Zigzag censuses, conducted an average of four 

 times (range = 0-9) per month in each section of 

 the study area, were used to estimate population 

 size. A zigzag census was conducted by piloting the 



•'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Manuscript accepted January 1980. 

 FISHERY BULLETIN: VOL. 78. NO. 3, 1980. 



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