possibility of thermally-induced stress, perhaps 

 lowering resistance to opportunistic infection; 

 however, clinical evidence is lacking due to the 

 small sample size of fresh carcasses. Although 

 data are available for other species of marine 

 mammals (see reviews in Gaskin, 1982, and 

 Whittow, 1987) httle has been published on 

 thermoregulatory response of Tursiops tnincatus 

 in spite of its relatively long history of captivity. 

 Unpublished data suggest that the thermoneutral 

 Tninimnm for TuTsiops truncatus is approximately 

 4-5 °C, but may vary with acclimation (S. H. 

 Ridgway, pers. comm., December 1991). 



o 



a 



X 



s 



o 

 o 



150 



OFFSHORE TOANSPORT 



FigOTB 6: Monthly bottlanosc dolphin ■trmndingi a* m 

 function of oSihorc trmnsport along Texaa coast, iphng 

 1986- 19M. (Only months with mora than on* reported 

 stranding w«r« used.) 



Alternatively, the observed association 

 between sea surface temperature and bottlenose 

 dolphin stranding may be less direct. Gunter 

 (1941, 1952) noted increased fish mortahties in 

 the Texas Gulf Coast region associated with cold 

 weather. Decreased food availabihty could affect dolphin health. An estimated 2.7 million 

 fish, of which approximately 2.6 milHon were striped muDet (Mugil cephalus), died in East 

 Matagorda Bay after a severe cold spell in December 1989 and smaller fish kills occurred 

 in Texas Bays fi-om Sabine to Lagima Madre Bay; however, there was no evidence of a 

 similar fish kill in the Gulf of Mexico (pers. comm., Larry McEachron, Fish Resources 

 Program, Texas Parks and Wildlife Dept., Rockport, TX, March 1991). 



Striped mullet are reported to be a prey item of bottlenose dolphins in the northern 

 Gulf of Mexico (Gunter, 1942; Leatherwood, 1975); however, these reports are contradicted 

 by more recent studies (Barros and OdeU 1990, and Barros, Section FV, this report). It is 

 possible that, because of unusual weather-related fish migration patterns or fish mortalities, 

 bottlenose dolphins were forced to switch to alternative prey items which may have been 

 nutritionally inadequate. Data regarding fish migration during December 1989-March 1990, 

 were unavailable. All but one of the 38 stranded bottlenose dolphins examined had food 

 in their stomachs (Barros, Section IV, this report), and comparison of prey items among 

 Texas-stranded dolphins from earher dates showed no significant differences in prey species. 



An inverse relationship between spring bottlenose dolphin stranding rale and offshore 

 currents (Ekman transport) suggests the possibility of an apparent spring mortahty increase. 

 An increase in beach-cast dolphin mortalities may merely reflect an increased probability of 

 washing ashore due to onshore Ekman transport during the spring. Alternative^, an 

 apparent increase in mortality rate could occur with a seasonal increase in the nearshore 

 bottlenose dolphin population; however, this did not appear to be the case (see Hansen, 

 Section III, this report). 



42 



