The findings, coordinated on the Barcelona–Tanger–Barcelona route by professors Odei Garcia-Garin and Manel Gazo of the Faculty of Biology and the Biodiversity Research Institute (IRBio) at the University of Barcelona, are striking in their scale and simplicity. Between June and July, three scientific campaigns recorded a total of 707 observations of marine megafauna along 19 fixed shipping routes in the western Mediterranean and the Adriatic. The species recorded were mainly the eight cetaceans commonly present in the Mediterranean: the fin whale (Balaenoptera physalus), the sperm whale (Physeter macrocephalus), Cuvier’s beaked whale (Ziphius cavirostris), the common dolphin (Delphinus delphis), the bottlenose dolphin (Tursiops truncatus), the striped dolphin (Stenella coeruleoalba), Risso’s dolphin (Grampus griseus) and the long-finned pilot whale (Globicephala melas). Two species of sea turtle were also documented: the loggerhead seaturtle (Caretta caretta) and the green seaturtle (Chelonia mydas).

What makes the SYNFONY approach technically powerful is its reliance on fixed routes sailed repeatedly and simultaneously across a wide geographic area. Because the ferries follow the same transects on every campaign, each survey functions like a repeated sampling grid laid over the sea. When all routes are surveyed within the same narrow time window, the resulting dataset provides a broad, simultaneous snapshot of where cetaceans and sea turtles are concentrated at that moment. This is a fundamental advantage over opportunistic sightings or single-vessel surveys, which tend to sample different areas at different times and therefore struggle to distinguish real shifts in animal distribution from simple differences in survey effort. In effect, the commercial ferries become genuine platforms for observing marine biodiversity, gathering data on the presence and distribution of species along the routes they regularly sail.

The human dimension of the project is equally notable. More than 20 volunteers have taken part in the campaigns, mainly students from the University of Barcelona’s degree programmes in Biology, Marine Sciences and Environmental Sciences. These trained observers stationed aboard the ferries carry out the systematic visual surveys that generate the data. The project is carried out with the support of ferry lines and shipping companies, whose cooperation transforms routine passenger services into a monitoring network of remarkable reach. Garcia-Garin and Gazo emphasized the importance of this collective effort, thanking all the volunteers who, as observers on board, made the campaigns possible, as well as the shipping companies and all the people and institutions who contributed to the development of the project, noting that their participation and commitment is key in continuing to expand knowledge of Mediterranean marine biodiversity and advancing its conservation.

Among the clearest results of the campaigns is evidence that distribution patterns can change dramatically between one survey and the next, over intervals of only a few weeks. The striped dolphin offers a vivid example. Garcia-Garin and Gazo, from the UB’s Department of Evolutionary Biology, Ecology and Environmental Sciences, explained that during the first campaign the species was observed more frequently and across a wider distribution area, whereas in the third campaign the sightings were much more spatially concentrated, especially on one of the routes in the Spanish corridor. Such rapid contraction and concentration of sightings suggests that these animals respond quickly to shifting environmental conditions, prey availability or other pressures, and that any static picture of their distribution is likely to be outdated within a season.

The fin whale, the Mediterranean’s only regularly occurring baleen whale and an emblem of the basin’s open waters, told a different story. The number of fin whale sightings remained relatively stable across the three campaigns, but the researchers found that the species’ distribution along the different routes underwent considerable changes. In other words, the overall abundance of observations stayed roughly constant while the locations where the whales were detected shifted substantially between campaigns. This decoupling of abundance from distribution is precisely the kind of pattern that only a synoptic, repeated-transect design can detect reliably, and it carries direct implications for conservation measures such as the placement of speed restrictions or the timing of protective measures in whale aggregation areas.

Sea turtles added further evidence of rapid spatial variability. The loggerhead turtle was the most frequently observed taxon across the entire monitoring period, underscoring its prominence in the Mediterranean’s surface waters. However, the experts noted that the number of observations decreased from the first campaign to the subsequent ones, while changes in its distribution within the network of monitored routes were also detected. Because loggerhead turtles are highly vulnerable to bycatch and vessel strikes, knowing when and where they concentrate, and how quickly those concentrations move, is essential information for fisheries managers and shipping operators alike.

SYNFONY does not operate in isolation. The project is being developed as part of the Fixed Line Transect Mediterranean Monitoring Network (FLT Med Net), coordinated by the Italian Institute for Environmental Protection and Research (ISPRA), of which IRBio-UB has been a member for almost 10 years. This broader initiative draws on more than two decades of experience in collaboration with shipping companies, meaning that the new campaigns rest on a long institutional foundation rather than a one-off effort. The integration of university researchers, national environmental agencies and private ferry operators represents a model of how large-scale marine monitoring can be achieved without dedicated research vessels, which are expensive to operate and limited in geographic coverage.

The practical motivation behind all this data collection is the growing overlap between maritime traffic and marine megafauna. Shipping is one of the pressures that may overlap spatially and temporally with the presence of cetaceans and turtles, whether through the physical risk of collision, underwater noise or other disturbances. The data obtained by SYNFONY can contribute to developing new dynamic risk assessment models that integrate the presence of the species, the intensity of maritime traffic and environmental conditions within a single framework. Unlike static maps that fix protection zones in place year after year, dynamic models can adjust predictions as animals move and as traffic patterns change, allowing management measures to follow the risk rather than lag behind it.

The researchers’ stated aim is to be able to identify more precisely which areas and which periods present a potential increased risk to marine megafauna and to advance towards a better understanding and management of the Mediterranean marine space. In a sea shared by dozens of nations, intense shipping lanes and a fragile community of long-lived, slow-reproducing species, that goal is ambitious. But the message from the 707 sightings gathered in just a few weeks of ferry-based observation is clear: the Mediterranean’s whales, dolphins and turtles are not stationary, and the tools used to protect them must be just as mobile as the animals themselves. With volunteers, universities, agencies and shipping companies pulling in the same direction, the region now has a working template for watching its giants in near real time.

Subject of Research: Ferry-based monitoring of cetacean and sea turtle distribution in the Mediterranean Sea

Article Title: Tracking the fin whale and the sperm whale in the Mediterranean

Article References: Tracking the fin whale and the sperm whale in the Mediterranean. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: fin whale, sperm whale, striped dolphin, loggerhead turtle, Mediterranean Sea, marine megafauna, ferries, SYNFONY, University of Barcelona, maritime traffic, cetacean survey, dynamic risk assessment

The technical challenge of studying diving animals at sea is formidable. Sea turtles are air-breathing reptiles, and although they can remain submerged for extended periods, they must return to the surface to breathe. That dependency means they occupy much of the vertical space in coastal and neritic habitats, putting them in harm’s way wherever fishing gear is set, from surface longlines to bottom trawls. The lungs of a turtle play a dual role, storing oxygen and controlling buoyancy, which shapes how the animals dive and rest. To untangle these behaviours, the team used Wildlife Computers SPLASH10-385 C transmitters, instruments capable of logging depth at 0.1 metre resolution and temperature to within 0.1 degrees Celsius at five-second intervals. The onboard data were compressed and transmitted in hour-long snapshots through the low-bandwidth Argos satellite system, with tags limited to 250 transmissions per day, producing a stream of time-series depth and temperature records spanning the turtles’ migrations.

The three turtles, labelled I, J and K, were captured in May 2023 in Kyparissia harbour using the established turtle rodeo technique. To guarantee that only actively breeding adult males were tagged, the researchers targeted individuals observed mounted upon or attempting to mount other turtles, a reliable behavioural indicator of breeding males. Once ashore, each turtle’s carapace was sanded, cleaned with acetone and fitted with an epoxy-and-fibreglass transmitter attachment. The tags then recorded each animal’s post-breeding movements: turtle I migrated east into the northern Aegean Sea near Thasos Island, turtle K settled in the Argolic Gulf on the eastern Peloponnese, and turtle J travelled north through the Ionian Sea before establishing two sequential foraging sites in the Adriatic. Transmission durations ranged from 98 days for turtle I to an impressive 547 days for turtle J, the only individual tracked long enough to reveal a full seasonal cycle.

The depth data revealed a striking pattern: despite differences in destination, all three turtles overwhelmingly favoured shallow water. Turtle I spent 98.6 percent of its time shallower than 10 metres and over 99 percent shallower than 20 metres. Turtle K and turtle J were more adventurous, spending 55.3 and 62.3 percent of their time above 10 metres respectively, yet both still exceeded 99 percent of their time within the top 80 metres. Even turtle J, the deepest diver of the trio, which twice plunged beyond 200 metres, reaching 201.5 metres in August 2023 and a remarkable 288 metres in September 2023, spent 95 percent of its life above 70 metres. For fisheries managers, this is the crucial message: turtles concentrate their lives in narrow vertical bands, and gear positioned away from those bands is far less likely to intercept them.

Temperature proved to be a powerful driver of behaviour. Summer sea surface temperatures peaked near 29 degrees Celsius in July and August, and the turtles registered short-term spikes well above ambient values, occasionally approaching 45 degrees, which the authors interpret as surface basking rather than true water temperature. More intriguing were the thermal structures the turtles swam through. The time-series data captured shallow thermoclines at around 9 metres and deeper ones near 35 metres, and when a distinct deep thermocline was present, the turtles altered their diving, executing multi-depth dives that clearly separated warmer shallow phases from colder deep phases. Turtle J lived in waters with a notable deep thermocline for more than 30 consecutive days, sometimes rising above the boundary to hold steady at about 30 metres for 20 to 30 minutes, behaviour that may represent warming up after foraging in colder water below, or movement along the seafloor between thermal layers. Such responses to thermoclines have never previously been reported for Mediterranean sea turtles.

Daily rhythms also shaped the animals’ vertical lives. During warm periods, the turtles showed classic diel patterns: relatively active, erratic diving by day and longer, quieter resting dives at night, or in some cases the reverse, with one turtle performing nocturnal resting dives at 30 metres and deeper daytime dives beyond 70 metres. These patterns likely reflect shifts between nocturnal refuge and daytime foraging, though the available tracking resolution cannot fully separate behavioural change from movement between sites. The study classified the dives using a standard lettered nomenclature for sea turtle dive profiles: steady Type A dives suggesting rest, variable-bottom Type B dives indicating activity, Type E profiles associated with thermoclines, and the rare Type C plunge, a rapid straight descent followed by an immediate ascent, exemplified by turtle J’s 288-metre excursion. The purpose of such extreme dives remains uncertain; comparable dives elsewhere have been interpreted as exploratory, navigational or prey-searching, but the authors candidly note that without direct observation, much interpretation rests on what they describe as speculation and guesswork.

Winter transformed the picture entirely. As waters cooled through November into April, turtle J, the only animal still transmitting, shifted to spending far more time at depth, with dives regularly exceeding one hour and the longest, repeated dives surpassing three hours between 19 and 21 February 2024, with no clear day-night rhythm. This is consistent with cold-induced dormancy: cooler water slows reptilian metabolism, reducing oxygen demand and allowing extraordinary breath-holding. Loggerheads are the champions of cheloniid endurance, with reported winter dives of up to 614 minutes. Yet a subtle finding complicates the dormancy story. Even when diving deeper than 50 metres in midwinter, turtle J rarely encountered water below about 15 degrees Celsius, recording values below that threshold on only three days, with a minimum of 14.2 degrees. The 15-degree mark has long been proposed as a trigger for overwintering behaviour in sea turtles, though empirical support has been lacking, and the authors note that deeper waters are thermally buffered from surface variability, a stability visible even in slight nocturnal thermal inversions where the surface was about one degree cooler than the water below.

The conservation implications are immediate and practical. Fishing activity in the Mediterranean is estimated to catch around 132,000 turtles annually, killing roughly 44,000 as bycatch or through entanglement in lost ghost gear. Because turtle depth use varies with season and temperature, the authors argue that management tools such as depth limits and soak-time restrictions should evolve dynamically with seasonal sea temperatures rather than remaining static. In colder months, quiescent turtles resting on the seafloor become especially vulnerable to bottom trawling, while in warmer periods most of a turtle’s time is spent in the top few metres, suggesting that deeper-set nets and hooks could dramatically reduce encounters. Similar depth-based strategies have informed longline management in the Pacific, and tracking of loggerheads from Crete has already suggested that setting gear below 5 metres could cut bycatch, though outcomes remain untested. Beyond fisheries, knowing what fraction of time turtles spend at the surface is essential for correcting aerial and boat survey counts for availability bias, adjustments that can inflate abundance estimates nearly twentyfold.

There is also an unexpected bonus: the turtles themselves are ocean observers. Their tags returned depth-linked temperature profiles reaching down to about 80 metres, echoing findings from loggerheads in the northwest Atlantic, and such animal-borne data can refine remotely sensed sea-surface temperature products and contribute to climate forecasting. The authors acknowledge the limits of their study; with winter data from a single individual, they deliberately avoided quantitative analysis, and two of the three tags stopped transmitting early, probably dislodged or damaged rather than a sign of turtle injury. But the 2,426 hours of paired depth and temperature data from turtle J alone demonstrate what is possible. Future work with more tracked males and finer-scale sensors should disentangle the effects of temperature, season, time of day and seabed depth on behaviour, enabling better predictions of how these animals will redistribute their lives as the Mediterranean warms. For now, the message from three roaming males is clear: protect the narrow, shallow, temperature-shaped band where they actually live, and one of the sea’s most iconic survivors gains a fighting chance.

Subject of Research: Depth use and thermal environment of adult male Mediterranean loggerhead sea turtles tracked by satellite

Article Title: Depth use and thermal environment of adult male Mediterranean loggerhead sea turtles

Article References: Rees, A. F., Batzios, P., Dendrinos, P., Dimalexis, T., Mikoniatis, G., Paxinos, O., & Vavassis, Y. (2026). Depth use and thermal environment of adult male Mediterranean loggerhead sea turtles. Discover Conservation, 3(1), Article 22. https://doi.org/10.1007/s44353-026-00091-1

Image Credits: AI Generated

DOI: 10.1007/s44353-026-00091-1

Keywords: loggerhead turtle, Caretta caretta, Mediterranean Sea, satellite tracking, diving behaviour, thermocline, bycatch, fisheries management, Kyparissia Bay, sea temperature, conservation, Argos telemetry