Research by the University of East Anglia (UEA) revealed the daily habits of the endangered Mediterranean sperm whale. Unmanned underwater gliders, equipped with acoustic monitors, recorded the sounds or “clicks” of the sperm whale for several months, studying thousands of kilometers of the ocean. Sperm whales are vocal whales: they produce different types of clicks for social interaction and echolocation. The study, published today in the journal Endangered Species Research, focused on the extremely powerful and targeted “normal clicks” produced during feeding.
New recordings of the sounds of sperm whales have confirmed their widespread presence in the northwestern Mediterranean. They also identified a possible hotspot for the sperm whale in the Gulf of Lyon, where a higher click rate was found. This may indicate a greater number of whales, but may also be due to behavioral reasons.
In addition, continuous day and night monitoring during the winter months suggest different strategies for whale foraging in different areas. In the Ligurian Sea, mobile and independent whales forage at any time of the day. In the Sardinian Sea, common clicks were also found at any time of the day.
Research has also shown a clear 24-hour pattern with the least effort for whales to forage at dawn. This may indicate that they may have changed their usual diet at any time to accommodate the availability of local prey. This gives an idea of the diet of the sperm whale in this area.
Fewer than 2,500 mature individual Mediterranean sperm whales are now at risk. Threats to them include by-catch in fishing nets and, as recently off the coast of Italy, entanglement in illegal fishing gear. Other hazards include ship collisions and the ingestion of marine debris.
The study involved researchers from the UEA and the Center for Environment, Fisheries and Aquaculture Sciences (CEFAS), the Scottish Association of Marine Sciences (SAMS), the University of Gothenburg, and the Sorbonne University.
Lead author Pierre Cauchy, a research fellow at the Center for Ocean and Atmospheric Research (COAS) of the UEA and CEFAS, said their findings would help conserve whales.
More sightings, especially during the winter months, will help scientists better understand their habitats to ensure proper management of shipping and fisheries.
A clear diurnal pattern found in our results suggests that sperm whales are adapting their foraging strategy to the behavior of local prey. The results also point to a geographic pattern of their daily behavior during the winter.
The study included the analysis of sounds recorded by smart robots – passive acoustic monitoring sensors (PAMs, Pluggable Authentication Modules), previously successfully used to observe weather, on gliders deployed by the team to collect oceanographic data in the winter of 2012-2013 and June 2014, covering 3,200 km.
Professor Karen Heywood, also from COAS, said the study demonstrated the feasibility of using existing glider missions to monitor the Mediterranean sperm whale during the winter months, which lacks important data for conservation.
The addition of PAM sensors to existing oceanographic glider flights provides the opportunity for continuous long-term surveillance, which will significantly improve monitoring of the sperm whale population and description of behavior, as well as identification of key habitats and potentially harmful human interactions, the scientists concluded.