Vessel collisions with small cetaceans worldwide and with large whales in the Southern Hemisphere: building a standardized database. Scientific Committee document SC/58/BC6, International Whaling Commission, May-June 2006, St.Kitts

We compiled and reviewed 248 cases of reported vessel collisions with small cetaceans worldwide and with large cetaceans in the Southern Hemisphere. Difficulties were encountered with the comparison of highly variable data in terms of quality (evidence), sources, detail and degree of authentication. It is recommended that wide agreement be reached on a minimum dataset template. We propose 25 standardized parameters, including an essential ‘probability tag’ (confirmed, probable, possible and indeterminate) that categorizes likelihood of vessel strike as evaluated by the original observer(s). Since the time-consuming process of fact-checking and standardizing is ongoing, any elaborate quantitative analysis is premature. Among baleen whales in the Southern Hemisphere, ship collisions have definitely accounted for deaths of southern right, blue, sei, fin, Bryde’s and humpback whales. In South Africa, an estimated 20% of mortality in Eubalaena australis is due to vessel strikes (Best et al., 2001). Accumulating evidence suggests the problem to be severe also in Argentina, Brazil and Uruguay, but small samples impede estimation of incidence. Odontocetes regularly affected include sperm whale, killer whale and common bottlenose dolphin. At least one or a few vessel strikes are documented for 19 species of small cetaceans (several for the first time): Kogia breviceps, Orcinus orca, Globicephala melas, G. macrorhynchus, Tursiops truncatus, Sousa chinensis, Orcaella brevirostris, Cephalorhynchus hectori, C. commersonii, Lagenorhynchus australis, Stenella frontalis, Neophocaena phocaenoides, Phocoena spinipinnis, Phocoena phocoena, Lipotes vexillifer, Platanista gangetica, Ziphius cavirostris, Berardius arnuxii and Mesoplodon grayi. Three species with suspected involvement in accidents include Sousa plumbea, Mesoplodon hectori and M. bowdoini. For some 11 small cetacean species the effect of collisions on populations is thought to be insignificant. Among estuarine species, at least two populations of each S. chinensis (Xiamen and Hong Kong/Pearl River) and O. brevirostris (Mahakam River and Chilika Lagoon) are significantly impacted. Mahakam population mortality is definitely not sustainable (2.9% minimum annual mortality). For L. vexillifer of the Yangtze river and P. gangetica, because of extremely low population numbers, even a very few mortalities may reduce likelihood of future survival. In Hong Kong’s N. phocaenoides, 9.4% of carcasses showed blunt traumatic injury consistent with boat collision. Two calves C. hectori were killed by boats near Banks Peninsula in 1999, a major concern considering its endangered status. Around 2% of T. truncatus in the Gulf of Guayaquil showed scars and mutilations of dorsal fins, caused by at least partly by propellers. Boat based dolphin-watching, such as in Chile and Costa Rica may adversely affect local T. truncatus populations. Overall, considering the high incidence of injuries and mortality caused by propellers, a much wider use of propeller guards is advised