The angel shark is a flat shark living on coastal sandy bottoms. Once common throughout the Mediterranean and the North-East Atlantic, it is today one of the most threatened species in the world (critically endangered according to the IUCN) and as such constitutes an emblem of marine biodiversity in danger.
[Article issu de The Conversation, écrit par Eric Durieux, Maitre de Conférences HDR en Écologie marine, Université de Corse Pascal-Paoli, Caroline Bousquet, Assistante scientifique, Office de l’Environnement de la Corse, Johann Mourier, Professeur junior en Ecologie comportementale des poissons, Université de Montpellier]
The angel shark, which even gave its name to the Baie des Anges in Nice, had been missing for decades from the French coasts, but that was without counting on the island of beauty, where it found a true refuge. If you indulge in a conversation with the fishermen from the ports of Bastia to Solenzara, they are unanimous: the angel shark has always been and is still present on the coasts of Corsica. And that's good news.
This shark has large lateral fins, reminiscent of the wings of an angel, and can spend several hours stuck in the sand waiting for its next meal. Like many shark species, its reproduction rate is slow (8 to 10 months of gestation), the number of young per litter is low (7 to 25 pups), and its sexual maturity is late, making it particularly vulnerable to pressures. anthropogenic.
Corsica, last refuge of the angel
The angel shark thus disappeared from more than 90% of its territory during the 20th century.e century, victim of intensive fishing, particularly bottom trawling, and the destruction of its habitat. While it was traded, the species has been protected since 2010 in all European Union waters. It was long thought that the Canary Islands were the last refuge in the world for this shark, but the knowledge of local Mediterranean – and therefore Corsican – fishermen tells a completely different story.
In Corsica, this species, as discreet as it is fascinating, seems to have a preference for the large expanses of sand of the eastern plain. And for good reason: the low fishing effort – mainly artisanal – coupled with an ideal habitat made up of hundreds of square kilometers of sand, several estuaries and one of the largest Posidonia meadows in the Mediterranean, classified as a Natura 2000 site and coordinated by the Corsican Environment Office. Artisanal fishermen, present at sea as soon as the weather permits, are true sentinels of the sea, and as such are regular observers of this species.
The valuable expertise of artisanal fishing
The objective was therefore to set up a partnership between scientists and artisanal fishermen to improve knowledge of this iconic species in Corsica. This project entitled Corsic'Ange (started in 2022) aimed in particular to better understand the distribution and spatio-temporal dynamics of the species in Corsica, on the one hand thanks to the empirical knowledge of fishermen and on the other hand by highlighting places specific monitoring at the population level by conventional marking and at the individual level by electronic marking to understand its movements and behavior.
First of all, it was a question of combining the memory of fishermen with scientific information, to carry out an inventory of the presence of the angel shark in Corsica.
Imagine a coastline 150 kilometers long – what you need to reach Paris and the Normandy coast – and a stretch of 5 kilometers off these coasts. This is where we seek to study the angel shark. Suffice to say that looking for a species on the verge of extinction in such a large area is like looking for a needle in a haystack.
It is therefore towards small-scale coastal fishermen that we turn to study this species. Their years of experience spent offshore save valuable time: they know perfectly when and where to find them. It is with a few of them that we learn that the species is present all year round on the coasts up to a hundred meters deep, but that gatherings of several dozen individuals take place in winter and spring period.
How many are there and how is the population structured?
Identifying the functional zones of the species (reproduction, nursery, resting place and migration corridor) is fundamental to improving conservation measures. The reproduction of the angelshark, in particular, is very little documented and only one nursery area has so far been located in the Canary Islands.
The partnership with fishermen continued with Capture/Marking/Recapture (CMR) monitoring on the eastern coast of Corsica, ultimately making it possible to estimate the size of the population. Accidentally captured angel sharks were fitted with an individual “spaghetti” type tag and then released. In 18 months of monitoring, 214 angel sharks were tagged and 19 were recaptured, for a recapture rate of 9.7%, which already seems to indicate a population of significant size.
This monitoring also made it possible to better understand the structure of this population, in terms of distribution of young of the year, juveniles, subadults and adults. Sightings vary seasonally, more frequent in spring and summer with mainly adults and subadults, while juveniles are more often encountered in winter. Newborns have also been observed as some females sometimes give birth on board fishing boats. These observations are the first evidence that could confirm the presence of a nursery area on the eastern coast of Corsica.
These data also made it possible to identify a new potential area of attendance north of Cape Corsica in summer 2023, with two individuals captured, one of which already marked in the waters of the north of the eastern plain. This recapture revealed that angel sharks can travel up to 70 km over the course of a year. The movements of tagged sharks vary, with some remaining faithful to one area from year to year, while others travel greater distances.
How can we study the behavior of this species?
We know that it favors sandy and muddy areas up to approximately 150 m deep, even if it most often remained between 10 and 50 m, and that juveniles and pregnant females frequent the entrances to estuaries and the brackish waters. However, the behavior of this species in particular in the Mediterranean is very little known.
To understand their lifestyle, acoustic telemetry monitoring was carried out between July 2022 and November 2023. A transmitter (tag) was placed on 28 individuals, measuring between 63 cm and 1.20 m. Here again, the capture and marking here electronically relied on the close partnership with the fishermen.
The frequentation areas, identified by fishermen, were crisscrossed with 58 acoustic receivers (fixed hydrophones) between Bastia and Solenzara. Of the 28 sharks tagged, 24 were detected by the hydrophone network: 7 males and 17 females.
Although no north/south migration has yet been evidenced on the eastern plain, migration from the depths to the coasts is indeed taking place. The angel shark would frequent the Posidonia meadow and deeper waters in summer, then the coasts and river mouths in autumn/winter.
The angel shark's home ranges are divided into two zones: the home range and the central zone of activity. The home range is the area comprising the majority of its movements, the one that it will use 95% of its time to meet its needs in search of food and reproduction. His central zone of activity represents the area he will use 50% of his time and represents his preferred zone.
The analyzes carried out highlight that the size of the home range is impacted by the size of the shark. The larger the individuals, the larger the home ranges will be.
The sex of the animal is also a determining criterion. Males tend to have a larger home range: on average 60 km2 against 35 km2 for females. The central areas of activity are smaller, with around 13 km2 for males and 8 km2 for females. These differences can be explained by the tendency of males to mate with several females and thus be more active in the search for partners, increasing movements.
Over the entire period studied, angel sharks were most often detected stationary, that is to say stuck in the sand, during the day and at night. This indicates that their swimming activity would not be greater at night, as one might suppose, and that these sharks spend almost 75% of their time in the sand.
There are still a few exceptions… Certain sharks, in the minority, are detected most often at times when they are moving. For other rare individuals, such as a female marked in the summer of 2022, the activity rates are reversed with significant silting time during the day and very significant swimming activity at night.
These still preliminary observations have not yet highlighted all the behaviors of the species; since then other data have been collected which will allow us to improve the estimation of the vital territories and activity rhythms of the species. 'species.
The results of this study bode well! Working with professional fishermen is essential to better understand one of the last populations of this species on the verge of extinction on a global, Mediterranean and national scale. The continuity of the monitoring initiated in Corsic'Ange is essential and will make it possible to estimate the size of the population, its genetic connectivity with the Greek, Libyan and Atlantic populations, but also the differences in behavior at the individual level and between related individuals. . The partnerships established within the Angel Shark Project provide new study perspectives and new methodologies. The improvement in knowledge provided by this scientific-fishermen partnership contributes to promoting the conservation of the angelshark in Corsica by directly involving local stakeholders, as well as more widely in the Mediterranean and throughout its range.
With an unwavering passion for local news, Christopher leads our editorial team with integrity and dedication. With over 20 years’ experience, he is the backbone of Wouldsayso, ensuring that we stay true to our mission to inform.
