FISHERY Bl'LLKTIN: VOL. 86. NO. 4 



percentage of calves in September, a second autumn 

 peak cannot be ruled out. 



Resighting of 26% of the identifiable bottlenose 

 dolphins in 2 successive years is evidence that some 

 of these return to the same area. Although the prob- 

 ability of resighting individuals twice in 2 successive 

 years is low if the individuals are transient, knowl- 

 edge of the length of stay is required to infer 

 seasonal residency. A study similar to that con- 

 ducted on bottlenose dolphins in Argentina (Wiir- 

 sig and Wiirsig 1978) could provide information on 

 the length of individual residency and should be con- 

 sidered. This would facilitate interpretation of the 

 data presented here, as well as that gathered from 

 currently ongoing surveys. 



Because of the violation of several important 

 assumptions, the accuracy of the density and abun- 

 dance estimates reported here is difficult to assess. 

 The CETAP (1982) summer average density esti- 

 mate of nearshore Tursiops in the mid-Atlantic 

 region was 0.0093 dolphins/km^. This is much 

 lower than my estimate of 0.159 dolphins/km- in 

 the Chesapeake Bay mouth and 3.446 dolphins/km- 

 in the southern coastal region. Besides differences 

 in survey altitude and airspeed, one possible reason 

 for this discrepancy is the larger area surveyed dur- 

 ing the CETAP program. If the coastal Tursiops 

 are generally found close to shore (within 2 km) and 

 the area surveyed extends far beyond this distance, 

 then the density of coastal Tursiops in its typical 

 habitat will be underestimated. Alternatively, a 

 heterogeneous coastal distribution could account for 

 this discrepancy. 



The importance of an average bottlenose dolphin 

 density estimate which may be used as an index of 

 abundance has recently been emphasized by an inci- 

 dence of disease which resulted in the deaths of over 

 200 Tursiops along the Virginia coast and over 400 

 along the Mid- Atlantic Bight during the summer of 

 1987.^ The rather large gap in the coastal Tursiops 

 abundance data base renders assessment of the im- 

 pact of the 1987 mortalities on local Tursiops stocks 

 problematic. Future monitoring of the coastal Tur- 

 siops may provide answers as to the rate of recovery 

 and allow assessment of the impact of future catas- 

 trophic events. A coordinated, long-term program 

 to monitor coastal Tursiops abundance would per- 

 mit temporal comparisons of abundance indices and 

 provide a greater understanding of natural popula- 

 tion fluctuations. Because the coastal Tursiops 



^J. G. Mead, Division of Mammals, Smithsonian Institution, 

 Washington, DC, pers. commun. June 1988. 



inhabit an area where human activity is rapidly in- 

 creasing, such a monitoring program should receive 

 high priority. 



ACKNOWLEDGMENTS 



I greatly appreciate the participation of R. Bow- 

 man, S. White, and especially R. A. Byles in the 

 aerial surveys. J. G. Mead provided welcome advice 

 and imparted to me much of his personal knowledge 

 of the bottlenose dolphin, for which I am grateful. 

 S. T. Buckland and T. D. Drummer graciously pro- 

 vided me with Fortran programs for line transect 

 analysis. My thanks to J. A. Musick, R. A. Byles, 

 G. P. Scott, and anonymous Fishery Bulletin re- 

 viewers who made especially helpful comments and 

 suggestions on earlier drafts of the manuscript. This 

 study was conducted under contract No. NA-80- 

 FA-D-0008 to H. M. Austin from the National 

 Marine Fisheries Service, NOAA, and an assistant- 

 ship to the author from the Virginia Institute of 

 Marine Science. 



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