Individuals size estimations of the sperm whales from the Gulf of Taranto (Northern Ionian Sea, Central Mediterranean Sea) employing clicks’ Inter-Pulse-Interval (IPI) measurements

For the purpose of conserving vulnerable species included in the Habitats Directive as well as species indicating the state of ecosystem health, according to the Marine Strategy Framework Directive, regular basis information on their populations and demography trends are necessary. In this study, an indirect assessment of the individual size and age of sperm whales sighted in the Gulf of Taranto (Northern Ionian Sea, Central Mediterranean Sea) was carried out by means of acoustic analysis of the Inter-Pulse-Interval (IPI) values of the clicks recorded from June to November 2020. The open software CABLE was employed to calculate first the IPI of the animals, then their body length, using two different equations. The obtained size estimates were then compared with ones visually made by observers on the field. The results show that, except for two individuals of 13 m and 14 m in length, most of the recorded animals are individuals of 8 m-10 m in length, corresponding to the age class of mature females or young males. An evaluation of IPIs of sperm whales recorded in different Mediterranean areas will allow verifying if most Mediterranean sperm whales belong to younger age classes indicating that the population is still recovering from the past centuries of direct catch.