m in the channel, but generally are 6-10 m. Region 4, Boca Ciega Bay, includes a 

 complex of barrier islands, shallow seagrass meadows, and channels. Water depths 

 up to 7 m may be found in the channels, but the waters are typically much more 

 shallow. Region 5, Tampa Bay northeast of the Sunshine Skyway Bridge, is the 

 largest region, including the mostly undeveloped southeastern shoreline of Tampa 

 Bay and associated mangrove/seagrass shallows, the main shipping channel, and to 

 the northwest the highly developed St. Petersburg shoreline. The ship channel is 

 dredged to about 14 m, but most of the region is 2-8 m in depth. Old Tampa Bay, 

 Region 6, is an open bay region crossed by three bridge/causeway systems. In the 

 south, channels reach 8 m in depth, but most of the waters are less than 4 m deep. 

 Region 7, Hillsborough Bay, is the most extensively altered portion of Tampa Bay. To 

 the east, heavy industry has impacted much of the shoreline, and dredge spoils from 

 the shipping channel have Tilled significant portions of the bay. To the north, 

 dredge and fill activities associated with shipping and with the development of Tampa 

 have defined the shoreline. Influx of water from the polluted Hillsborough and 

 Alafia Rivers, as well as from occasional industrial waste spills, have adversely 

 impacted the water quality in this region. Water depths outside of the channel 

 average less than 5 m. Gulf and Sarasota Bay waters adjacent to the Tampa Bay 

 Regions 1-7 were also surveyed to address the questions of immigration and 

 emigration. 



Survey Schedule 



A six-week window during September-October was selected to provide ample 

 opportunity to fully survey each region of the study area at least three to five times. 

 Surveys were initiated in early September and were continued into October for as 

 long as was logistically feasible to complete the desired level of coverage. This 

 timing was selected for several reasons. Late summer-early autumn historically 

 brought a period of calm weather, providing a window of favorable survey 

 conditions before the cold fronts begin to penetrate southward into central Florida. 

 The timing was also considered to be advantageous for natality estimates. In adjacent 

 waters to the south, most of the year's calves were born by September-October (Wells 

 et ad. 1987). Based on an assumption of similar patterns of reproductive seasonality in 

 Tampa Bay and Sarasota, it seemed that a late summer-early autumn survey would 

 provide the best estimate of numbers of calves born during that year (young-of-the- 

 year). Previous surveys conducted during this period found a peak in abundance 

 (Scon et aV. 1989; Weigle 1990). The timing of our surveys thus allowed us to take 

 advantage of high dolphin densities, and to be able to compare our findings with 

 those from previous surveys. 



Additional information on the occurrence of identifiable dolphins in Tampa 

 Bay was provided by surveys in support of a dolphin reintroduction study (Bassos 

 1993). Data from outside of the NMFS survey period each year were not included in 

 quantitative analyses for this report, but provided perspective. 



Field Techniques and Logistics 



Surveys were conducted from 6-7 m outboard-powered boats. Two, three, or 

 four boats were used during each survey. Each boat was equipped with a VHF radio, 

 depth sounder, compass, thermometer, and eventually a hand-held LORAN. Survey 

 crews ranged in size from two to six people per boat. Survey routes were selected 

 each day based on predicted weather conditions and the status of survey coverage. 

 While searching for dolphin schools, the boats were operated at the slowest possible 

 speed that would still allow the vessel to plane, typically 33 to 46 km/hr, depending 



