SECTION m 



POPULATION ABUNDANCE AND STRANDINGS 



Lany J. Hansen 



Southeast Fisheries Science Center 



Miami Laboratory 



75 Virginia Beach Drive 



Miami, FL 33149 



Methods 



Estimates of bottlenose dolphin abundance from large-scale aerial surveys of the Gulf 

 of Mexico (Scott et al. 1989) were compared with historical stranding data. Seasonal 

 estimates were available for fall (September-October 1983), winter (January-February 1984), 

 spring (April-May 1984), and summer (July-August 1984) for the northwestern Gulf. For the 

 northeastern Gulf, seasonal estimates were available for fall (September-October 1985), 

 winter (January-February 1986), and simimer (June-August 1985). The estimates were 

 stratified by the following zones: bay (embayments and inshore of barrier islands), inshore 

 (seaward of the coast or embayment boundaries to the 18.3m isobath), and offshore (18.3m 

 isobath to 9.3km seaward 

 of the 182.9m isobath). 

 The area surveyed is 

 shown in Figure 1. 



An aerial survey of 

 a portion (Block 154) of 

 the northwestern Gulf 

 inshore zone along Texas 

 and Louisiana was 

 conducted during March, 

 1990, in response to the 

 1990 anomalous mortality 

 event (see Appendix IV 

 for details). This area, and another adjacent portion of the inshore zone (Blocks 152 and 153) 

 and an adjacent portion of the offshore zone (Block 054 and B) were surveyed during June, 

 1990, in response to the MEGABORG oil spill (see Appendix IV). The estimated abundance 

 for these areas sampled in 1990 was compared to the survey results from during 1984. 



Fignrc 1: Aerial »urvcy blocks of the northern Gulf of Mexico used during 1983-86 NMFS 

 regional surveys for bottlenose dolphins (Scott et al^ 1989), and blocks surveyed dunng 

 1990 (152, 153. 154, 054, B). 



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