Abstract
Epimeletic behavior has been classified as 'nurturant' if care-giving behavior is demonstrated, especially toward a young animal, and 'succorant' if the animal appears to be "helping" an animal in distress.2 Nurturant epimeletic behavior characterized by the carrying of dead neonates has been observed in wild Texas bottlenose dolphins by the TMMSN in 1994 and documented by Fertl and Schiro.2
In the first quarter of 2008, the Texas Marine Mammal Stranding Network (TMMSN) experienced an Unusual Mortality Event (UME) declared by NOAA/NMFS during which the TMMSN recovered 85 Atlantic Bottlenose Dolphin carcasses in two counties on the upper Texas Gulf Coast. Evidence of possible nurturant epimeletic behavior exhibited on the carcasses of Tursiops truncatus neonates was observed and photographed. Bruising was noted on the ventral surface of the necks of neonates in various stages of decomposition with total body lengths ranging from 75 cm to 119 cm. The bruising is characterized by a discoloration of the skin ranging from a greenish-brown to reddish-purple. The shape and size of the bruises on the ventral side of each carcass is consistent with the average mandibular width of adult T. truncatus, also collected from the upper Texas Gulf Coast. Adjacent to the areas of the bruising are punctures and indentations, which by size and placement are consistent with wounds made by dolphin teeth. Parallel linear lines approximately 1 cm apart (rake marks) consistent with the teeth of T. truncatus were also noted on the pectoral fins on the carcasses mentioned above.
The above observations are thought to be evidence of adult T. truncatus from the Gulf of Mexico carrying dead neonates in their mouth by grasping them around the ventral side of the neck or their pectoral fins. Previously documented nurturant behavior has almost always been directed towards young animals.1 Forty-five of the 85 carcasses recovered by the TMMSN were between the lengths of 75 cm to 125 cm, and 17 out of those 45 show discolorations resembling bruises from the possible nurturant epimeletic behavior described above. Necropsies were performed on all 17 neonates with decomposition ranging from early to late stages. Unlike the evidence of infanticide described by Dunn et al.3 and Patterson et al.,4 necropsies of the 17 calves did not reveal evidence of blunt-force trauma--there were no observed broken ribs, fractured scapulas, or spinal dislocations. This information, paired with direct observations of nurturant epimeletic behavior in Texas coastal dolphins2 and elsewhere, suggests that infanticide was not the cause of the post-mortem findings discussed in this abstract. Based on examination of injuries inflicted on bottlenose dolphins from boat strikes, fisheries interaction, predation, and scavenging, it is unlikely that the bruising described in this abstract are a result of the aforementioned activities.
References
1. Felix F. 1994. A case of epimeletic behaviour in a wild bottlenose dolphin Tursiops truncatus in the Gulf of Guayaquil, Ecuador. Investigations on Cetacea. G. Pilleri (ed). Vol. XXV, Pp. 227-234.
2. Fertl D., and A. Schiro. 1994. Carrying of dead calves by free-ranging Texas bottlenose dolphins (Tursiops truncatus). Aquat Mamm 20(1): 53-56.
3. Dunn D.G., S.G. Barco, D.A. Pabst, and W.A. McLellan. 2002. Evidence for infanticide in bottlenose dolphins of the Western North Atlantic. J Wildl Dis 38(3): 505-510.
4. Patterson I.A.P., R.J. Reid, B. Wilson, K. Grellier, H.M. Ross, and P.M. Thompson. 1998. Evidence for infanticide in bottlenose dolphins: an explanation for violent interactions with harbour porpoises? Proc R Soc Lond B 265: 1167-1170.