Behaviour and vocalizations of two sperm whales (Physeter macrocephalus) entangled in illegal driftnets in the Mediterranean Sea

Abstract

Illegal driftnetting causes each year several entanglements and deaths of sperm whales in different Mediterranean areas, primarily in the Tyrrhenian Sea. In summer 2020, during the June-July fishing season, two sperm whales were found entangled in illegal driftnets in the Aeolian Archipelago waters, Southern Italy. These two rare events were an exceptional chance to collect behavioural and acoustics data about entangled sperm whales. We analysed 1132 one-minute sets of breathing/behavioural data and 1575 minutes of acoustic recording, when the whales were found entangled, during the rescue operation, immediately after release, and in the days thereafter. The first whale was generally quiet showing a general status of debilitation/weakness, numerous skin lesions, and low breathing rate (0.31 (0.60)); it collaborated during rescue operations. On the contrary, the second whale showed a high level of agitation with a high breathing rate (1.48 (1.31)) during both the entanglement period and the net cutting operations, vigorously moving its fluke and pectoral fins, opening its mouth, sideway rolling or side fluking and frequently defecating. Acoustically, the first whale produced mainly single clicks in all phases except for two series of creaks during rescuing operations while the second whale produced a wide range of vocalizations (single clicks, likely either slow clicks or regular clicks, creaks, and codas). Our observations indicate that acoustics, respiratory and behavioural parameters may be useful to monitor the physical/physiological status of sperm whales during disentanglement operations.

Genomics reveals the role of admixture in the evolution of structure among sperm whale populations within the Mediterranean Sea

“…However, Mazzariol et al (2011) found several hooks within stomach content analyses of stranded sperm whales, suggesting possible feeding activity along fishing lines as described in some oceanic regions (e.g., Jacobsen et al, 2010). At the same time, fishery activity can also impact sperm whales through entanglement in fishing nets (e.g., Blasi et al, 2021;Pace et al, 2008).…”

“…However, Mazzariol et al (2011) found several hooks within stomach content analyses of stranded sperm whales, suggesting possible feeding activity along fishing lines as described in some oceanic regions (e.g., Jacobsen et al, 2010). At the same time, fishery activity can also impact sperm whales through entanglement in fishing nets (e.g., Blasi et al, 2021; Pace et al, 2008). Ghost nets, ship collision and the ingestion of plastic debris are the three main impacts that are seriously threatening these endangered sperm whales in the Mediterranean Sea (Alexiadou et al, 2019; de Stephanis et al, 2013; Frantzis et al, 2019).…”

Threatened cetaceans off the coast of Israel and long‐range movement of a sperm whale

“…Genetic data show that there is a distinct subpopulation in the Mediterranean that is listed as Endangered by the IUCN, with fewer than 2500 mature animals (Pirotta et al, 2021; Violi et al, 2023). Threats in the Mediterranean include ship strikes, interactions with fisheries, underwater noise from seismic surveys or military operations and ingestion of marine debris (Blasi et al, 2021; Frantzis et al, 2019; Notarbartolo di Sciara & Gordon, 1997; Notarbartolo‐Di‐Sciara, 2014; Rendell & Frantzis, 2016). In many regions, particularly the eastern Mediterranean, sperm whale numbers, distribution and threats remain poorly understood, and more research effort is needed considering that some degree of isolation between western and eastern Mediterranean has been recently assessed (Violi et al, 2023).…”

Passive acoustic monitoring of sperm whales and anthropogenic noise using stereophonic recordings in the Mediterranean Sea, North West Pelagos Sanctuary

“…Like the eight common cetacean species inhabiting the Northwestern Mediterranean Sea, sperm whales evolve in a highly anthropized environment 3 . Sharing an environment with a dense human activity implies threats for the animals such as bycatch 4 , 5 , vessel collisions 6 , or ingestion of solid debris 7 . Besides the latter, one of the main anthropic pressure in the marine environment is acoustic 8 .…”