Why are whales found stranded on the Catalan coast?

The last Friday of May, bathers and rod fishermen on Trabucador beach were stunned to see the body of a fin whale, almost 11 meters long, stranded on the sand a few meters from the Badia dels Alfacs beach. The animal, which was eventually returned to open sea, had multiple serious injuries compatible with a collision with a boat's propeller. A few days later, the lifeless body of a sperm whale in an advanced state of decomposition and with clear signs of having suffered trauma arrived on the beach of Les Botigues de Sitges.The stranding of large cetaceans on the Catalan coast is not a common sight, but in no case is it an isolated event, especially in recent years. One element that can explain this is the interaction of two high-density traffic routes between the peninsula's coast and the Islands. On the one hand, the Mediterranean cetacean migration corridor passes through this area, recognized and protected as a migration space for these animals; and, on the other hand, it is the entry route for vessels to three of the most important ports in the Mediterranean, those of the cities of Valencia, Tarragona, and Barcelona.Double danger: collisions and noise pollution  

"In recent years, the biggest threat to the common rorqual and the sperm whale is maritime traffic and underwater noise, which can come from both traffic itself and from oil operations or sonar tests," explains Miriam Romagosa, a researcher at the Institute of Marine Sciences specializing in cetacean acoustics, about one of the reasons for whale strandings on the Catalan coast. The recurrent death of large cetacean specimens is especially relevant considering that some of the Mediterranean whale species are listed as endangered, such as the common rorqual and the sperm whale. These two are among the most common on the Catalan coast and, in the case of the common rorqual, it is the second largest animal in the world. The threat to this group of mammals is growing. From 1992 to 2012, maritime traffic has quadrupled, and technological development has made vessels much faster, a fact directly related to the mortality of large aquatic mammals. "In fact, regarding collisions, the biggest problem is speed. From 14-15 knots, mortality rises drastically due to the severity of the traumas that occur. At these speeds, mortality is between 80 and 100%", asserts Romagosa. Vessels such as ferries and cargo ships often exceed them.This speed makes it almost impossible for large cetaceans, with much slower movements than other aquatic mammals like dolphins, to be able to avoid boats. Collisions with maritime traffic, resulting in trauma or injuries, represent 20% of the reasons for strandings recorded in the northeast Mediterranean, a very high percentage, according to the scientist. Even so, the vast majority of whales that die at sea sink without a trace. This makes it difficult to quantify the magnitude of the problem and understand the current impact of interaction with maritime traffic. The whales are calling

But beyond the visible collisions on the bodies of stranded cetaceans, whales have an invisible enemy: underwater sound. It is not surprising that some of these animals that reach the Catalan beaches show no sign of having suffered an impact. The head of the clinical and rescue area of the CRAM Foundation, Lucia Garrido, recalls that "all animals that reach the coast do so because they have some pathology that makes them have a poor state of health. Simple disorientation does not cause them to strand on the beach". For whales, hearing is the fundamental sense that allows them to communicate, orient themselves, feed, and mate. This is why the acoustic pollution produced by maritime traffic, oil exploration, or sonar tests has effects that condition their behavior. In this regard, it has been observed that these species tend to increase the speed and duration of their dives, and that they indefinitely suspend habits such as feeding. A study published in May, which analyzed 1,336 communications from 18 cetaceans in an area with high anthropogenic pressure, has found that these animals have to call out to be able to communicate with each other.It also has immediate effects. In 2002, during NATO naval exercises, 14 beaked whales beached in the Canary Islands, specifically on the islands closest to where the exercises were taking place. They used medium-frequency sonars for anti-submarine training. The animals' necropsies revealed decompression effects. "The widely accepted theory is that it was caused by the animals suspending their dives upon hearing the sonar and suddenly surfacing. After this incident, tests of this type were restricted in the Canary Islands and there have been no more mass strandings of these species," points out Romagosa. Alerts for boats, a solution?

Despite everything, the technology and knowledge to prevent the death of these species are already possessed. Part of the solution is being developed by the team led by Arantza Ugalde and Miriam Romagosa from the Institute of Marine Sciences of Barcelona, with co-financing from the Pure Ocean Foundation. The method the researchers have found involves using the existing fiber optic cables installed on the seabed. "An equipment called an interrogator is connected to these cables, which sends light pulses through the fiber optic cable and analyzes the returning signal. Whale vocalizations or the noise of a vessel generate acoustic waves and vibrations that can induce small deformations in the fiber, which are recorded in the optical signal. In this way, the fiber can act as a network of distributed sensors on the seabed," explains researcher Ugalde, who is an expert in the use of submarine cables for seismic monitoring. All this information has the potential to generate an alert system for ships when the sounds produced by common rorquals or other whales to communicate are identified and located. But implementing this measure would not only have benefits for biodiversity and endangered species, but would also achieve a reduction in the economic impact on vessels due to collisions with cetaceans. "Most medium-sized vessels are completely aware of the vast majority of whale collisions, and it is common for them to have to return to port or stop to make repairs to propellers and ship hulls," says Romagosa. Even so, Garrido recalls that part of this threat to the ecosystem exists due to the current commercial and economic system: it is estimated that 80% of the volume of goods exchanged worldwide arrives by sea. "Consuming locally and from businesses that do not depend on a large volume of imports reduces dependence on goods arriving by sea, generating less environmental impact and, in turn, reducing maritime traffic which is directly related to the disorientation of whales," concludes the head of the clinical and rescue area of the CRAM Foundation.