UNIT 24 

 MARINE MAMMALS OF THE ATLANTIC REGION AND THE GULF OF MEXICO 



ics L(infirniL-d that some individual dolphins re- 

 main in the same general areas within Matagorda 

 Bay, Texas, throughout the year (Lynn, 1993); 

 thus, the situation there may be similar to that ot 

 the Florida west coast. Movement ot resident 

 bottlenose dolphins in Texas through passes link- 

 ing bays with the GulF ot Mexico appears to be 

 relatively limited, but does occur and suggests that 

 these communities, like those along the Florida 

 west coast, may not be reproductively isolated from 

 the coastal populations. For example, two bottle- 

 nose dolphins previously seen in the South Padre 

 Island, Texas, coastal area were seen in Matagorda 

 Bay, 285 kilometer north, in May 1992 and May 

 1993. Preliminary analyses of mitochondrial DNA 

 using polymerase chain reaction procedures sug- 

 gested that Matagorda Bay dolphins appear to be 

 a localized population, despite the suggestion ot 

 mixing ot some individuals over large distances 

 (NMFS, unpublished data'). Over 1,000 indi- 

 vidual bottlenose dolphins have been identitied 

 in bay and coastal waters near the northeast end 

 ot Galveston Island, Texas, but most ot these were 

 sighted only once with only 200 individuals re- 

 ported to use the area over the long term, suggest- 

 ing that a significant number ot dolphins are not 

 resident in this area. 



Much less is known about the movements ot 

 resident bottlenose dolphins in estuaries ot the 

 northern Gulf of Mexico. Seasonal differences in 

 bottlenose dolphin abundance in Mississippi 

 Sound suggest seasonal migration; however, these 

 migration patterns are yet to be fully described. It 

 is probable that some exchange occurs between 

 the Mississippi Sound communities and the coastal 

 dolphins in this area as well. 



Population Size 



Population size tor all ot the provisional stocks 

 except Sarasota Bay, Florida, was estimated from 

 preliminary analyses of line-transect data collected 

 during aerial surveys conducted in September- 

 October 1992 in Texas and Louisiana, in Septem- 

 ber-October 1993 in Louisiana, Mississippi, Ala- 



'Nation.il M.irinc I'lshcrics Service, Northcist Fisheries Sci 

 ence Center, l(i(> W.uer Street. Woods Hole, MA 02S4.^ 



bama, and the Florida panhandle, and aerial sur- 

 veys of the west coast of Florida in September- 

 November. Population estimates for the Sarasota 

 Bay, Florida, community were obtained through 

 direct count of known individuals. Minimum 

 population estimates were calculated trom the es- 

 timates ot population size and their associated co- 

 efficients of variation (Table 24-1). Where the 

 population size resulted from a direct count ot 

 known individuals, the minimum population size 

 was identical to the estimated population size. 



Current Population Trend 



Population data are insufficient to determine 

 trends for the provisional stocks of bottlenose dol- 

 phin that inhabit the bays, sounds, and estuaries 

 in the Gulf of Mexico. However, three anomalous 

 mortality events occurred among portions ot these 

 communities between 1990 and 1994. While these 

 events may have resulted in declines in some loca- 

 tions, it is not possible to accurately partition the 

 mortalities between the bay, sound, and estuary 

 communities and adjacent coastal dolphin com- 

 munities. Thus, the effect ot these mortalit)' events 

 on the growth ot these populations cannot be de- 

 termined at this time. Ongoing monitoring will 

 be required to establish more accurate populations 

 estimates and, over time, trends in abundance for 

 these dolphin communities. 



Status of Stock 



In the absence of information on population 

 trends and unknown status for Gult bay, sound, 

 and estuary bottlenose dolphin communities, 

 PBR's are calculated using a recovery tactor ot O.SO. 

 The estimates tor each provisional stock are given 

 in Table 24-1. 



Although these provisional stocks are not listed 

 as threatened or endangered, the occurrence ot the 

 three anomalous mortality events within their 

 communities is cause for concern. While the spe- 

 cific tactors that presumably caused and or con- 

 tributed to these mortalir)' events has yet to been 

 determined, evidence suggests that bottlenose dol- 

 phins m the northern and western coastal portion 

 of the U.S. Gulf of Mexico may have experienced 

 a morbillivirtis epidemic in 1993 (Lipscomb, 



251 



