Comparison of echolocation behaviour between coastal and riverine porpoises

Abstract: Echolocation behaviour of a harbor porpoise and six finless porpoises was recorded in open-water systems using acoustic data loggers (A-tag). In total 1359 click trains were recorded during 4.6h for the harbor porpoise and 46,240 click trains were recorded during 82.3h for the finless porpoises. The harbor and finless porpoises produced sonar click trains every 12.3 and 6.4s on average, respectively. During the inter-click-train interval, the porpoises were silent or produced clicks below 148dB re. , the detection threshold of the tag. Ninety percent of the inter-click-train intervals were 20s or less in both species. This means that porpoises frequently produce intense click trains. Click-train intervals lasting over 50s constituted 1% of the total intervals in finless porpoises and 4% in the harbor porpoise. Both species swam without intense clicks for less than 10m in most cases, but occasionally remained silent or used undetected low-intensity clicks for more than 1min. During these periods, the porpoises would be susceptible to entanglement in fishing nets. [Copyright &y& Elsevier]