Background

In 2002, Proyecto Toninas began the first systematic study of several aspects of the ecology and behaviour of toninas along the coastal zone of La Coronilla and Cabo Polonio, which are now part of the National System of Protected Areas (SNAP). Between 2002 and 2007, the studies aimed to find out how often toninas were observed on those beaches, describe their behaviour, and test the photo-identification technique to identify individuals through photographs of long-lasting natural marks on the dorsal fin (Würsig and Würsig 1977). During that same period, studies of the social structure of the groups also began — that is, how they are made up (adult, juvenile and calf individuals) and how photo-identified individuals associate with one another (whether there is any preference between individuals).

🐬💙🌊 Overall, more than half of the individuals in the tonina population show long-lasting marks on the trailing edge of their dorsal fin. These marks can be notches, cuts, depressions or colour changes that alter the profile of the fin. This is how researchers can identify each tonina individually. The marks may originate from interactions between animals during socialising or mating. They can also be caused by boat propeller cuts or entanglement in fishing nets.

📸 In Uruguay, more than 50 toninas have been identified through photographs of natural dorsal-fin marks (Laporta 2009, Laporta et al. 2016, Menchaca et al. 2019). Each tonina has a name and a corresponding number, and they are catalogued in a 📖 photo-identification catalogue, used to record the toninas observed in our waters and as a reference for comparison with other areas. Fin photos provide very valuable information about the abundance and movements of individuals in the population, how long each individual stays in a given area, association preferences, calving intervals, and other data.

Since 2017, Proyecto Toninas has been acoustically monitoring tonina groups in Uruguay, aiming to build a whistle catalogue. Within this work, it was found that toninas use a variety of whistle contours, mostly emitting multiloop, constant and upsweep whistles. The emission frequency range was between 4 and 11 kHz, and most whistles had a minimum frequency between 2.1 and 5.1 kHz, a maximum frequency below 12 kHz, and a duration under 600 ms (Menchaca 2018).

Listen to a whistle on the tonina species page →

In addition, a comparative whistle study together with colleagues from Brazil found that toninas from southern Brazil and Uruguay produce sounds that are more similar to each other than to those produced by toninas occurring in Rio de Janeiro, which could be explained by genetic divergence or environmental variance (Lima et al. 2020).