Sighting and video recording of a possible hybrid dolphin between Lagenorhynchus obscurus and Lissodelphis peronii at Golfo Nuevo, Pla.Valdés, Chubut, Argentina

Rafael J.Benegas *; Ricardo D.Orri *; Luis Pettite ** and Hugo P.Castello ***.
*Captain and owner of a whale watching boat, Ribera Marítima s/nº, Puerto Pirámides, Chubut; **Naturalist and Photographer; ***Marine Mammal Laboratory, Arg.Mus.Nat.Sc., A.Gallardo 470, 1405 Bs.As., Argentina.

During December 1998, at Golfo Nuevo, 4 miles from Puerto Pirámides, an approximately 2.20 m long non described dolphin was sighted from a boat by three of us (R.J.B.;R.D.O.;L.P.) interacting with a pod of dusky dolphins, Lagenorhynchus obscurus. During the first sightings, the dolphin swam at great speed and tried to avoid our boat becoming more curious later on. On 11/21/98 it was video recorded while swimming together with dusky dolphins. During several sightings, while actively swimming on the bow's wave or interacting with dusky dolphins and four species of marine birds, it preyed on anchoita, Engraulis anchoita or silverside fishes (Atherinidae) on the surface. Thanks to the water's transparency, it was possible to observe a non described adult dolphin, showing a body longer than the duskies, but similar in coloration and body shape to Lissodelphis peronii, with the exception of the beak that is not completely white, a black surrounded eye on the white area of the body, a tiny dorsal fin positioned nearer to the caudal fin, a grey or white middle stripe running up to the end of the caudal peduncle, more noticeable after the tiny dorsal fin, and differences on the distribution of the black cape. Since associations of L.peronii with dusky dolphins and pilot whales are known, we propose the hypothesis that a female L.obscurus and male L.peronii mated when pods of both species probably met in a middle point of their range. After the hybrid calf was born it stayed during lactation with his mother and was socially accepted by other dusky dolphins when adult. A hybrid between L.obscurus and Delphinus capensis has been described by Reyes (1996) for the coast of Perú. This is the first sighting of a natural hybrid between two species from different genera in the S.W.Atlantic. A 5 minutes long video will be shown.