Rough ray
Rough ray ventral side
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Superorder: Batoidea
Order: Rajiformes
Family: Rajidae
Genus: Raja
Species:
R. radula
Binomial name
Raja radula
Delaroche, 1809

The rough ray (Raja radula) is a Mediterranean ray species of the Rajidae family described by Delaroche in 1809.[2][3]

Description

The rough ray is named for the spinules that cover its upper surface. In juveniles and males, these rough spinules are only on the snout and the lower half of the tail.[4] The females of this species have spinules in these areas, but also around the mouth, along the mid-section, and the full tail.[4] These spinules differ from the thorns that are on the inner-eye and from the end of the head to before the dorsal fin. There are two thorns between the dorsal fins.[4]

The subcircular body has a short, curved snout, anterior edges are convex and the extremities are angular wings.[5] Most individuals are around 70 centimeters. The main upper surface colors are light brown and grey, with darker spots and lines.[4] There are two eye-spots with yellow rings and a thick outer darker ring with light dots, placed on either side of the spinal meridian at the level of greatest width of the body.[4] The underside of the ray is white with darkening edges, and some darker spots on the tail.

Distribution and habitat

Raja radula distribution (in red).[6]

Raja radula is a benthic species native to the Mediterranean Sea.[7] Some Atlantic records are probably misidentifications of Leucoraja naevus and/or Raja africana and need to be clarified.[8] This species inhabits coastal areas, between 2 and 300m depth on sandy or muddy bottoms of the continental shelf.[7][1]

Diet

This species seems to have short periods where they search for food and rapid digestion. Their diet consists mainly of benthic animals, such as crustaceans, teleosts, and mollusks.[9] Indeed, their main prey are crustaceans, such as decapods or amphipods, and the second are teleosts. It was found that diet remained relatively similar between individuals of different sexes, however, the size of the individual led R. radula to move from the consumption of crustaceans to teleosts.[9] The smaller individuals have a diet dominated by crustaceans as the medium size individuals. However, larger individuals seem to be specialized in teleosts. These changes in diet over their growth suggest that they have diet plasticity that can be explained by different energetic needs between younger and older individuals and as an adaptation to avoid competition for resources. Juveniles are active feeders during the day all over the year and have a higher metabolic rate than adults.[10]

Moreover, there is a difference in diet depending on the geographic location. These differences in diet between locations can be explained by the different distribution, abundance, density, and availability of the prey. Reproductive migration is common in elasmobranchs, as a consequence, they occupy different niches that may result in diet diversification. Raja radula has an active predator foraging behavior. Some pelagic species are found in their stomach content even if their morphology suggests that they can not prey on the water column. Thus, the hypothesis is that they also present scavenger behavior.[11][12] They are considered as specialized secondary consumers but with sufficient plasticity in the diet to adapt their consumption in the function of the preys available in the environment. Their trophic level may increase with their growth.

Reproduction

Like many other rays, R. radula presents an oviparous reproduction strategy, meaning that parents produce offspring by laying eggs. The eggs have a case of 5.1 to 5.7 cm long.[13] The embryos hatch in about 4 months.[4] This species reproduces throughout the year, with a peak in late spring/early summer.[4] The females and males become mature at different sizes: females are mature at 34 cm disc width and males at 30 cm disc width[14][4] This species reproduces throughout the year, with a peak in late spring/early summer.[4] The females and males become mature at different sizes: females are mature at 34 cm disc width and males at 30 cm disc width.[15][16][17] Half of the maturity is reached at 4.47 years for male individuals and 5.89 years for female individuals. Females can live until 12 years and reach 80 cm total length maximum while males can live 9 years and reach 65 cm total length maximum. The average length of 70 cm is therefore estimated to be reached at 9 years.

Locomotion

Raja radula on rocky bottoms.

Rays usually present a swimming mode, where the thrust generation involves the passing of undulatory waves (from anterior to posterior) along with the enlarged pectoral fins. However, this species presents a particular locomotion behavior: pelvic fin locomotion.[18] The pelvic fin cycle has two phases: a recovery and a propulsion phase. Left and right fins move alternatively during the recovery and they move in synchrony when punting.

During the recovery phase, one of the pelvic fins lifts off the bottom and protrudes anteriorly; the other fin firmly touches the bottom during the propulsion phase. No vertical undulations of pectoral fins occurs during asynchronous movements of the pelvic fins and the species held its body parallel to the bottom. The ray performs a general form of punting: although the fins were not entirely synchronous, the offset was minimal, and therefore, still considered punting. The rough ray is pushed off the bottom by a rapid powerful punt followed by the pectoral fin undulations. Although the left and right pelvic fin movements can be slightly offset, the movements are generally considered synchronous punts.

Conservation

Specimen held by a person.

The Mediterranean sea is subject to many pressures that endanger its biodiversity, particularly by urbanization and overexploitation. Like other elasmobranch species, Raja radula represents an important catch in the Mediterranean sea even if this species does not have any commercial value. Even if this species is not exploited or traded commercially, it is classified as Endangered (EN) according to the IUCN Red List.[1] Indeed, the greatest threat to this species is the by-catch[19] in demersal trawl, gillnet, trammel net, bottom longline, and purse seine fisheries. This bycatch occurs when fishing for cuttlefish, spiny lobster, red mullet, grouper, and Sparidae[20] mainly. In general, there are no conservation measures for this species. Indeed, it is not part of any education program, market control, or systematic monitoring scheme.[1] Furthermore, data on this species are often limited because when it is fished, the term "rays" or "stake" are recorded in the registry, which does not allow the determination of which species are fished. However, a study has shown that it is the sixth most commercially traded elasmobranch species in Palma de Mallorca.[21] This species is not registered in the CITES legislation from Species+ even when a decline of more than 50% is estimated. It is important to conduct further studies on this species to create accurate conservation programs for this endemic Mediterranean species.

See also

References

  1. 1 2 3 4 Mancusi, C.; Morey, G.; Serena, F. (2016). "Raja radula". IUCN Red List of Threatened Species. 2016: e.T161339A16527984. doi:10.2305/IUCN.UK.2016-1.RLTS.T161339A16527984.en. Retrieved 19 November 2021.
  2. ↑ Delaroche, F. (1809). Suite du mémoire sur les espèces de poissons observées à Iviça. Observations sur quelques-uns des poissons indiqués dans le précédent tableau et descriptions des espèces nouvelles ou peu connues. Annales du Muséum d'Histoire Naturelle, Paris. pp. 313–361.
  3. ↑ "Raja radula Delaroche, 1809". Global Biodiversity Information Facility.
  4. 1 2 3 4 5 6 7 8 9 "Marine species identification portal: Rough ray — Raja radula".
  5. ↑ Séret, Bernard (2010). Guide des requins, des raies et des chimères des pêches françaises. Ministère de l'Alimentation, de l'Agriculture et de la Pêche.
  6. ↑ "WoRMS - Raja radula Delaroche, 1809".
  7. 1 2 "Fishbase - Raja radula, Rough ray: Fisheries".
  8. ↑ Guide of Mediterranean Skates and Rays (Raja radula). Oct. 2022. Mendez L., Bacquet A. and F. Briand.http://www.ciesm.org/Guide/skatesandrays/raja-radula
  9. 1 2 Kadri, H.; Saïdi, B.; Marouani, S.; Bradai, M. N.; Bouaïn, A. (2013). "Food habits of the rough ray Raja radula (Chondrichthyes: Rajidae) from the Gulf of Gabès (Central mediterranean sea)". Italian Journal of Zoology. 80: 52–59. doi:10.1080/11250003.2012.697925. S2CID 85310216.
  10. ↑ Tiralongo, F.; Messina, G.; Gatti, R. C.; Tibullo, D.; Lombardo, B. M. (2018). "Some biological aspects of juveniles of the rough ray, Raja radula Delaroche, 1809 in Eastern Sicily (central Mediterranean Sea)". Journal of Sea Research. 142: 174–179. doi:10.1016/j.seares.2018.10.001. S2CID 92092918.
  11. ↑ Simpfendorfer, C. A.; Goodreid, A. B.; McAuley, R. B. (2001). "Diet of three commercially important shark species from Western Australian waters". Marine and Freshwater Research. 52 (7): 975–985. doi:10.1071/MF01017.
  12. ↑ Saidi, B.; Enajjar, S.; Bradaï, M. N.; Bouaïn, A. (2009). "Diet composition of smooth-hound shark, Mustelus mustelus (Linnaeus, 1758), in the Gulf of Gabès, southern Tunisia". Journal of Applied Ichthyology. 25: 113–118. doi:10.1111/j.1439-0426.2009.01306.x.
  13. ↑ Kadri, H.; Saidi, B.; Marouani, S.; Bradaï, M. N.; Bouaïn, A. (2013). "Age, growth and reproductive biology of the Rough Skate, Raja radula (Chondrichthyes: Rajidae), of the Gulf of Gabès (southern Tunisia, central Mediterranean)". Marine and Freshwater Research. 64 (6): 540–548. doi:10.1071/MF12218.
  14. ↑ Fischer, W.; Bauchot, M.-L.; Schneider, M. (1987). "Fiches FAO d'identification des espèces pour les besoins de la pêche. (Révision 1). Méditerranée et mer Noire. Zone de Pêche 37". Food and Agriculture Organization, Rome.
  15. ↑ Serena, F.; Mancusi, C.; Barone, M. (2010). "Field identification guide to the skates (Rajidae) of the Mediterranean Sea. Guidelines for data collection and analysis". Biologia Marina Mediterránea. 17: 204. doi:10.13140/2.1.2414.9764.
  16. ↑ Capapé, C. (1974). Contribution to the biology of Tunisian Rajidae. II. Raja radula Delaroche, 1809. Geographic and Bathymetric Distribution, Sexuality, Reproduction. Archives of the Pasteur Institute of Tunisia. pp. 211–228.{{cite book}}: CS1 maint: location missing publisher (link)
  17. ↑ Yeldan, H. (2005). "Identification of bioecological characteristics of some rays caught Raja clavata (Linnaeus, 1758), Raja asterias (Delaroche, 1809), Raja radula (Delaroche, 1809), Dasyatis pastinaca (Linnaeus, 1758) from İskenderun and Mersin Bays". Çukurova University, Science Institute, Ph.D. Thesis.: 153.
  18. ↑ Bilecenoglu; Murat; Ekstrom; Laura (2013). "Pelvic fin walking and punting behavior of Raja radula Delaroche, 1809 observed in the Sea of Marmara". Mediterranean Marine Science. 14: 158. doi:10.12681/mms.333.
  19. ↑ "FAO Species Identification cards: sharks and rays of the Mediterranean and Black Sea" (PDF).
  20. ↑ Morey, G.; Moranta, J.; Riera, F.; Grau, A. M.; Morales-Nin, B. (2006). "Elasmobranchs in trammel net fishery associated with marine reserves in the Balearic Islands (NW Mediterranean)". Cybium. 30: 125–132.
  21. ↑ Morey, G.; Navarro, O. (2010). "Monitoring of elasmobranch landings in Mallorca (Balearic Islands, NW Mediterranean). Identification at species level and understanding of the official statistics". Elasmobranch Association, Galway, Ireland.
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