Overview of sperm whale Physeter macrocephalus mortality events in the Adriatic Sea, 1555-2009

Abstract

1In the Mediterranean Sea, the sperm whale Physeter macrocephalus is one of eight regular cetacean species. Poor knowledge of its ecology and status, together with suspected decline in numbers, make studies of historical and present occurrence especially relevant. Long-term time series of stranding events are the most reliable data to provide a scientific framework for testing hypotheses that seek to explain the mechanisms responsible for cetacean strandings. 2We present a comprehensive overview of cases of sperm whale mortality and human response to such events encompassing five centuries (1555–2009) within a portion of the Mediterranean Sea that offers a wealth of historical information – the Adriatic Sea. 3A total of 36 mortality events were validated, involving 68 animals. Two findings of skeletal materials are also reported. The geographic distribution of strandings within the basin clearly was uneven: 44% of records (n = 16) were clustered along a 280km portion of the western Adriatic coast. A relatively high number of mortality events occurred along gently sloping sandy beaches away from suitable sperm whale habitat. 4Until the first half of the 20th century, live-stranded animals were routinely killed: all but one cases with known human response elicited killing attempts. Starting from the 1980s, killing was replaced by efforts to rescue the animals. 5Mass strandings of sperm whales have occurred since historical times in the Adriatic Sea. Mortality events involving multiple individuals accounted for at least 17% of the total sample (6 of 36 mortality events). At least 29% of live strandings (6 of 21) involved more than one individual. 6This study contributes a long-term dataset based on careful validation of historical information, suitable for hypothesis testing aimed at investigating spatial and temporal correlates of sperm whale strandings – particularly live strandings – as a clue to their causes.