ABSTRACT Risso's dolphins Grampus griseus and common bottlenose dolphins Tursiops truncatus typically occur in distinct habitats in the Mediterranean Sea. Along the Catalan coast (north‐eastern Iberian Peninsula), bottlenose dolphins are frequently observed nearshore and are often associated with fisheries, whereas Risso's dolphins typically inhabit deeper, offshore waters. Mixed groups of common bottlenose and Risso's dolphins and possible hybrids between the two species have been reported in certain areas, but never in the Mediterranean. Here, we describe an unusual sighting on the continental shelf in northern Catalonia: on 3 June 2025, a presumed Risso's dolphin calf was observed swimming in close association with an adult bottlenose dolphin, part of a group of 11 common bottlenose dolphins, while following a trawling vessel. The animal was seen swimming in an echelon position alongside one of the adult individuals. Given the rarity of the sighting, we consider two possible explanations for this observation: alloparental care and hybridisation. As the calf did not exhibit intermediate morphological traits, the evidence provides stronger support for the interspecific alloparental care interpretation; however, hybridisation cannot be definitively excluded in the absence of genetic confirmation. We also discuss potential factors contributing to spatial overlap between the two species. This observation may represent the first hybrid calf reported in the Mediterranean Sea, or may be the first documented case of alloparental care involving these species worldwide.
Amigó et al. (Mon,) studied this question.