AERIAL CENSUS OF THE BOTTLENOSE DOLPHIN, 

 TURSIOPS TRUNCATUS, IN A REGION OF THE TEXAS COAST 



Eric G. Barham,' Jay C. Sweeney,^ Stephen Leatherwood, Robert K. Beggs,'' and Cecilia L. Barham' 



ABSTRACT 



On five replicate aerial surveys in late March 1978, the bottlenose dolphin. Tursiops truncatus, herds 

 were sighted and their numbers estimated in 21 strip transects flown across bays and channels between 

 barrier islands and the coast from Port Aransas northeast to Matagorda, Texas. The transects were 

 spaced at 4.63 km intervals and herds were scouted in about 800 m wide strips totaling 436 km in 

 length, providing approximately 17% coverage of the area. On surveys 1-4 (survey 5 was excluded from 

 , population calculations because it was conducted in adverse weather) 133 bottlenose dolphin herds 



were sighted, containing an estimated 916 animals. Within these strips the mean heard size was 6.95 

 animals and mean herd density was 0.0947/km^, extrapolating to a population estimate of 1,319 

 dolphins and a density estimate of 0.752/km^ for the entire area. These figures are relatively high in 

 contrast to recent studies in other environments. About half the herds were feeding and approximately 

 one- third were traveling. Sightings were most frequent in ship channels, shallow areas inside barrier 

 islands, and near shore. There were several sources of bias in our measurements, and we consider the 

 results to be conservative. 



In the waters under jurisdiction of the United 

 States, live capture of marine mammals is now 

 limited by law to those species that are used for 

 public exhibition and scientific research. With the 

 exception of certain pinnipeds, the greatest de- 

 mand is for the bottlenose dolphin, Tursiops trun- 

 catus Montagu, the most tractable of the smaller 

 cetaceans. 



This recent management regime has generated 

 a need for assessment of marine mammal stocks 

 that consider population size and reproductive 

 rates of potentially impacted species (Odell et al. ). 

 Obviously, rigorous density estimates are an es- 

 sential starting point for such studies, but despite 

 the long history of a live fishery for bottlenose 

 dolphins (Townsend 1914) there are scant popula- 



'Southwest Fisheries Center. National Marine Fisheries Ser- 

 vice. NOAA, P.O. Box 271. La Jolla. CA 92038. 



^Dinnes Memorial Veterinary Hospital, 16133 Ventura 

 Boulevard, Encino. CA 91436. 



^Biomedical Branch, Naval Ocean Systems Center, San Diego, 

 Calif.; present address: Hubbs-Sea World Research Institute, 

 1700 South Shores Road, San Diego, CA 92109. 



"Sea Arama Manneworld. P.O. Box 3068. Galveston. TX 

 77552. 



'Department of Fisheries and Wildlife. Oregon State Univer- 

 sity, Corvallis, OR 97331. 



«Odell. D. K., D. B. Siniff, and G. H. Waring (editors). 

 1975. Tursiops truncatus assessment workshop. Final Report. 

 U.S. Marine Mammal Commission, Contract MM 5AC021. 141 p. 

 Rosenstiel School of Marine and Atmospheric Science, Univer- 

 sity of Miami, 4600 Rickenbacker Causeway , Miami, FL 33149. 



tion data on which to base management decisions 

 lOdell 1975). 



The majority of bottlenose dolphins that are 

 readily available for capture dwell in the coastal 

 and inland waterways of Florida and the other 

 states bordering the Gulf of Mexico. In such envi- 

 ronments several factors make T. truncatus, in 

 contrast to pelagic odontocetes, ideally suited for 

 synoptic studies from aircraft: many of the envi- 

 ronments are semienclosed waters of limited di- 

 mensions, the herds are usually small thus indi- 

 viduals can be relatively accurately counted, and 

 T. truncatus is generally the only small cetacean 

 in the area and therefore easily identified. Accord- 

 ingly, recent studies of bottlenose dolphins off the 

 northern Gulf of Mexico and the Indian River area 

 of Florida have used and refined aerial survey 

 tactics and methods (Leatherwood et al. 1978; 

 Leatherwood 1979; Leatherwood and Platter'; 

 Odell and Reynolds"). Using similar procedures 



M.'inuscnpt attt-pted .March 1979 



FISHERY BULLETIN: VOL. 77. NO. 3. 1980, 



'Leatherwood, S.. and M. F. Platter. 1975. Aenal assess- 

 ment of bottlenosed dolphins off Alabama. Mississippi and 

 Louisiana In D K. Odell. D. B. Siniff. and G. H. Waring 

 (editors). Tursiops truncatus assessment workshop, p. 49- 

 86. Final Report. U.S. Marine Mammal Commission. Contract 

 MM5AC021. Rosenstiel School of Marine and Atmospheric Sci- 

 ence, University of Miami, 4600 Rickenbacker Causeway, 

 Miami, FL 33149. 



"Odell.D K, and J. E.Reynolds in. 1978. Distribution and 

 abundance of the bottlenose dolphin, Tursiops truncatus, on the 

 west coast of Florida. Draft - Final Report, Marine Mammal 

 Commission, Contract MM5AC026, 55 p. Rosenstiel School of 

 Marine and Atmospheric Science, University of Miami, 4600 

 Rickenbacker Causeway, Miami, FL 33149. 



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