McFee and Hopkins Murphy: Strandings of Tursiops truncatus off Soutfi Carolina 



263 



1994; Barco et al., 1999). At about the same time, large 

 numbers of dolphins begin to appear along the "Grand 

 Strand" in northern South C'arolina (zone 1) in October 

 and peak in early November, according to bottlenose dol- 

 phin sighting data collected during photo-identification 

 studies (Wiung^). During the 1987 bottlenose dolphin die- 

 off, 52 bottlenose dolphin strandings were reported in 

 South Carolina from October through December (Wang et 

 al., 1994). Densities of bottlenose dolphins during a one- 

 year aerial survey of waters from the shore to the Gulf 

 Stream showed the greatest numbers of sightings in fall 

 1982 (concentrated in the Carolinas), and in winter 1983 

 (concentrated in northern Florida) (Wang et al., 1994). 



Stranding patterns may reflect the abundance of an- 

 imals. Although large numbers of dolphins occur year- 

 round in South Carolina, there appears to be a peak in 

 strandings in the late fall (November) which would coin- 

 cide with data from Myrtle Beach (Young^), Charleston 

 (Zolman, 1996), and Hilton Head Island (Petricig, 1994) in 

 which greatest abundance of dolphins occurred in late fall. 

 Water temperature, distribution of prey, and use of coastal 

 shrimp trawlers have been implicated as reasons for dol- 

 phin movements and abundance in certain areas (Kenney, 

 1990: Mead and Potter, 1990; Brager et al., 1994; Fertl, 

 1994). The late fall increase in the number of strandings 

 in South Carolina could be due to the increased numbers 

 of dolphins from any one of the migratory stocks suggested 

 in the above hypotheses. Zone 1, in particular, provided 

 evidence that a portion of the strandings is from a coastal 

 bottlenose dolphin migratory stock or stocks. The north- 

 ern half of zone 1 is known as the "Grand Strand" which 

 extends from N. Myrtle Beach to Murrells Inlet (approxi- 

 mately 59 km). This area is highly populated and animals 

 coming ashore here are found and reported regardless of 

 the season of the year. Coverage in the southern half of 

 zone 1 (approximately 78 km) tends to be high from May 

 to September when the beaches are monitored for sea tur- 

 tle nesting and hatching, but low during October to April. 

 However, the majority of strandings occurred during the 

 latter time period. This may suggest an influx of bottle- 

 nose dolphins migrating through zone 1 from October to 

 April, either from the north or south. 



We would expect bottlenose dolphin mortality to be simi- 

 lar to that for terrestrial mammals ( Ralls et al., 1980): high 

 neonatal and first-year mortality and high adult mortal- 

 ity, and an even distribution of mortality among males and 

 females. If stranding data reflect natural mortality pat- 

 terns, our results and other studies (Hersh and Duffield, 

 1990; Hersh et al., 1990; Wells and Scott, 1990; Fernandez 

 and Hohn, 1998) are consistent with mortality patterns 

 suggested for terrestrial mammals. Further, the percent- 

 age of stranded bottlenose dolphin neonates (19.6'^) was 

 intermediate when compared with that of previous studies 

 (observations in Sarasota, Florida, 36.8'+ [Wells and Scott, 

 1990], and Indian/Banana River System, Florida, 11.2% 

 IHersh et al, 19901 ), but similar to that of Texas (20. 0'^, 

 (Fernandez and Hohn, 1998] I. We can only assume that 



^ Young, R. 1998. Personal commun. Coastal Carolina Uni- 

 versity, P.O. Box 1954, Conway, SC 29526. 



mortality during the first year of life is high for bottlenose 

 dolphins regardless of geographical location. 



Age and ovarian analysis of stranded bottlenose dol- 

 phins >220 cm (Odell, 1975; Mead and Potter, 1990) are 

 necessary to determine whether these animals are sex- 

 ually mature and whether the seasonal patterns noted 

 above correlated with a seasonal reproductive cycle. Sea- 

 sonal reproduction cycles are complex and not well studied 

 in the South Carolina bottlenose dolphin population but 

 have been demonstrated where adaptations to local envi- 

 ronmental conditions may influence seasonal reproductive 

 cycles (Urian et al., 1996). 



Over large geographic regions, bottlenose dolphins ex- 

 hibit year-round calving cycles, but within small geograph- 

 ic regions there may be a higher degree of local reproduc- 

 tive seasonality (Urian et al., 1996). A unimodal seasonal 

 distribution of neonate bottlenose dolphin strandings was 

 noted from Sarasota, Florida, and along the Texas coast, 

 although peak neonatal strandings occurred in different 

 months of the year — May and March, respectively (Urian 

 et al., 1996; Fernandez and Hohn, 1998). A bimodal sea- 

 sonal distribution was noted for the east coast of Florida 

 in the Indian River Lagoon (Urian et al., 1996). In Sara- 

 sota, Florida births have been noted in every month of 

 the year (Urian et al., 1996). Although sample size over 

 the five-year period for our study was too small to esti- 

 mate significance of trends, our results showed a unimodal 

 distribution and a peak number in June. However, more 

 data may show a bimodal distribution of bottlenose dol- 

 phin neonatal strandings because of a second peak that 

 occurred in November. These peaks do not appear to be a 

 function of effort because the majority of neonate strand- 

 ings occurred on the banks of inland waterways or the 

 neonates were found as floating bodies. The number of 

 neonates in the Stono River estuary, Charleston, South 

 Carolina, peaked in the fall, during a 15-month photo- 

 identification study (Zolman, 1996). Further, all four neo- 

 nate bottlenose dolphins stranded in South Carolina in 

 November were <100 cm; therefore these animals may 

 have been aborted near-term fetuses. 



The determination of human interaction as the cause 

 of mortality for bottlenose dolphins is an important role 

 of the marine mammal stranding networks and can in- 

 fluence management decisions. For example, the Marine 

 Mammal Protection Act (MMPA), as amended in 1994, 

 required that annual stock assessment reports for each 

 stock of marine mammals be prepared. One of the items 

 to be addressed in these reports was a description of com- 

 mercial fisheries that interact with each stock and the 

 level of mortality caused on each stock by each fishery 

 (Waring et al., 1999). The level of mortality each fishery 

 contributes to a stock, in turn, is essential in determining 

 potential biological removal (PBR) estimates for the stock 

 and the subsequent classification category that regulates 

 each fishery (Waring et al., 1999). The current PBR for 

 Atlantic coastal bottlenose dolphins is 25 (Waring et al., 

 1999). In a study on the American shad iAlosa sapidis- 

 sima ) fishery in South Carolina from 1994 to 1995, no hu- 

 man interactions were shown to be a cause of bottlenose 

 dolphin mortality in the area of fishery effort (McFee et 



