Introduction 



The National Marine Fisheries Service (NMFS) is responsible for establishing 

 quotas for take of bottlenose dolphins ( Tursiops truncatus) and for monitoring the 

 populations of dolphins in the southeastern United States waters. Quotas have been 

 based on a rule-of-thumb developed by the Marine Mammal Commission in which the 

 annual quota has been set at 2% of the estimated dolphin abundance for a 

 geographical location. Most of the live-capture fishery for bottlenose dolphins has 

 occurred in the coastal Gulf of Mexico and the Florida east-coast waters. The NMFS 

 completed sampling surveys in these areas for abundance estimation, and recognized 

 a need for low-level monitoring of bottlenose dolphin stocks in southeastern US 

 waters, designed to detect catastrophic changes in the stocks. The main goals of the 

 monitoring were detection of large-scale changes in dolphin abundance and 

 establishment of archival databases for long-term trend detection. Low-level 

 monitoring could provide a short-term means of detecting large-scale changes in 

 population abundance and give decision makers the information necessary to 

 determine if modification of management plans is necessary. To these ends, in 1987 

 the NMFS began funding several local research efforts in the southeastern US with 

 the following stated objectives: 



1) Detection of large-scale (halving or doubling) interannual changes in relative 

 abundance and/or production of the bottlenose dolphin stocks in the southeast 

 US. The population rate parameters of relevance include: a reliable index or 

 estimate of local relative abundance, natality, mortality, emigration, and 

 immigration. 



2) Establishment of archival databases for long-term trend detection in localized 

 geographical regions around the southeast US. 



One of the regions selected by NMFS for low-level monitoring was Tampa Bay, 

 Florida. Prior to the regional aerial surveys conducted by NMFS during 1983-1986 

 (Scon et a/. 1989), no data were available to support any level of take from Tampa Bay 

 (Scott 1990). Several earlier aerial survey efforts included portions of Tampa Bay 

 and/or waters immediately offshore (Leatherwood and Show 1980; Odell and Reynolds 

 1980; Thompson 1981). Wells (1986) and Weigle (1990) conducted photographic 

 identification studies in parts of the bay, but there had been no complete systematic 

 estimation of the numbers of dolphins using Tampa Bay. NMFS regional aerial 

 surveys during June-August 1985 (= summer), September - October 1985 (= autumn), 

 and January - February 1986 (= winter) provided the first available estimates of 

 abundance for Tampa Bay proper (Scott et aJ. 1989, Table 26): 



Abundance Lower Upper 



Season Estimate 95% CL 95% CL 



Summer 198 78 318 



Autumn 248 148 348 



Winter 217 130 304 



The approach selected for the low-level monitoring of Tampa Bay dolphins was 

 photographic identification (photo-ID) surveys from small boats (see reviews by 

 Wursig and Jefferson 1990; Scott et al. 1990a). This technique has proven effective in 

 long-term studies of population-rate parameters in Sarasota Bay, immediately to the 

 south (Wells and Scott 1990). The large numbers of distinctive dolphins 

 photographed by Wells (1986) during surveys initiated in 1975, and later by Weigle 



