Small size in the common bottlenose dolphin Tursiops truncatus in the eastern Mediterranean: A possible case of Levantine nanism

The phenomenon of Levantine nanism in the Mediterranean Sea has so far been described in invertebrates and fish. We explored the possibility that it would also apply to marine mammals. To that end, we compared total body length (TBL) and skull condylobasal length (CBL) of adult common bottlenose dolphins Tursiops truncatus collected along the Israeli coastline (representing the Levantine subpopulation) to those of specimens collected along the shores of western Mediterranean seas. Significant differences were found between mean (±SD) CBL values of 40 skulls from Israel and a pooled sample of 40 skulls from the Adriatic, Tyrrhenian, Ligurian and Balearic Seas (49.70 ± 1.87 and 52.18 ± 1.47 cm, respectively, p < 0.001). The mean (±SD) TBL of 26 Israeli animals were significantly smaller than those of 28 animals from the Spanish Mediterranean coast and 36 animals from the French Mediterranean coast (272 ± 18.0, 317.3 ± 16.1 and 313.4 ± 14.8 cm, respectively, p < 0.001). The results clearly demonstrate that animals of the Levantine subpopulation are significantly smaller than those residing in the west. A difference of ~16% for TBL between populations fits the range of within-species dwarf morphs in cetaceans and, when translated into volume and mass, also fits the definition of Levantine nanism.