Common eagle ray

{{Speciesbox

| name = Common eagle ray

| image = Myliobatis_aquila.jpg

| status = CR

| status_system = IUCN3.1

| status_ref = {{cite iucn |author=Jabado, R.W. |author2=Chartrain, E. |author3=Cliff, G. |author4=Da Silva, C. |author5=Derrick, D. |author6=Dia, M. |author7=Diop, M. |author8=Doherty, P. |author9=Leurs, G.H.L. |author10=Metcalfe, K. |author11=Pacoureau, N. |author12=Porriños, G. |author13=Seidu, I. |author14=Soares, A.-L. |author15=Tamo, A. |author16=VanderWright, W.J. |author17=Williams, A.B. |author18=Winker, H. |date=2021 |title=Myliobatis aquila |volume=2021 |page=e.T161569A124508353 |doi=10.2305/IUCN.UK.2021-1.RLTS.T161569A124508353.en |access-date=20 November 2021}}

| fossil_range = {{Fossil range|2.588|Present}}

| image_caption =

| taxon = Myliobatis aquila

| authority = (Linnaeus, 1758)

| synonyms = *Leiobatus aquila (Linnaeus, 1758)

Myliobatis cervus Smith, 1935
Myliobatis equila (Linnaeus, 1758)
Myliobatis noctula Bonaparte, 1833
Myliobatus aquila (Linnaeus, 1758)
Raia rhombus Larrañaga, 1923
Raja aquila Linnaeus, 1758

| synonyms_ref = {{Cite WoRMS |title= Myliobatis aquila |id=105860 |access-date= 1 April 2023 }}

}}

The common eagle ray or bullray (Myliobatis aquila) is a species of fish in the family Myliobatidae. It inhabits the eastern Atlantic Ocean (North Sea to South Africa), the Mediterranean Sea and the south-western Indian Ocean.

Description

The common eagle ray reaches up to {{convert|183|cm|ft|abbr=on|1}} in total length{{cite web |title=Myliobatis aquila: Common eagle ray |url=http://www.fishbase.org/summary/4330 |accessdate=5 June 2016 |publisher=FishBase}} and has a disc width up to {{convert|80|cm|ft|abbr=on}}.Muus, B., J. G. Nielsen, P. Dahlstrom and B. Nystrom (1999). Sea Fish. p. 76. {{ISBN|8790787005}} Most specimens are, however, smaller.{{Cite book |last=Zsilavecz |first=Guido |url=https://www.worldcat.org/oclc/70133147 |title=Coastal fishes of the Cape Peninsula and False Bay: a divers' identification guide |date=2005 |publisher=Southern Underwater Research Group |isbn=0-620-34230-7 |location=Cape Town |oclc=70133147}} Females grow to be larger than males.{{Cite journal |last=Christian |first=C. |date=1976-05-01 |title=Etude du regime alimentaire de l'Aigle de mer, Myliobatis aquila (L., 1758) des cotes tunisiennes |url=https://academic.oup.com/icesjms/article-lookup/doi/10.1093/icesjms/37.1.29 |journal=ICES Journal of Marine Science |language=en |volume=37 |issue=1 |pages=29–35 |doi=10.1093/icesjms/37.1.29 |issn=1054-3139}} The dorsal surface is brown or black while the ventral surface is white. It has a rhomboidal disc with a pair of large, triangular pectoral fins projecting on either side, and a single dorsal fin. The blunt snout is rounded and the tail is long and slender, with a large spine at its base but no tail fin. On average, males have 72 spine serrations and females have 66 spine serrations. The spine makes about 70% of the male's length and 65% of the female's length.{{Cite journal |last=Schwartz |first=Frank J |date=2005 |title=Tail spine characteristics of stingrays (order Myliobatiformes) found in the northeast Atlantic, Mediterranean, and Black Seas |journal=Electronic Journal of Ichthyology |volume=1 |pages=1–9}} The mid dorsal groove, which contains the glandular tissue necessary for venom injection, extends along 10–40% the tail.{{Cite journal |last=Maretic |first=Z. |date=1982-01-01 |title=Some clinical and epidemiological problems of venom poisoning today |url=https://dx.doi.org/10.1016/0041-0101%2882%2990241-0 |journal=Toxicon |language=en |volume=20 |issue=1 |pages=345–348 |doi=10.1016/0041-0101(82)90241-0 |pmid=6123162 |bibcode=1982Txcn...20..345M |issn=0041-0101}} It has one or two excretory channels for the venom.Kumar, R & Vennila, R & Palani, Damotharan & Shankar, Kanchana & Muthuvel, Arumugam & Thangavel, Balasubramanian. (2010). Abundance of stingrays in parangipettai coast and the importance of exploring properties of their venom. Inter. Jour. of Recent Scientific Research.

Distribution and habitat

This species occurs in the eastern Atlantic Ocean, including the North Sea, from the British Isles to South Africa, extending to the Indian Ocean. It is also found in the Mediterranean Sea.Guide of Mediterranean Skates and Rays (Myliobatis aquila). October 2022. Mendez L., Bacquet A. and F. Briand. http://www.ciesm.org/Guide/skatesandrays/Myliobatis-aquila It occurs both close to the shore and further out, at depths down to about {{Convert|800|m|ft|abbr=on}}, but much of its time is spent in shallower water at less than {{Convert|50|m|ft|abbr=on}}. It typically prefers more open sandy areas. It has also been found in a semi-enclosed lagoon on Gran Canaria Island, particularly in winter (March to April) and summer (August to October), where it was founded to prefer rocky and mixed bottoms.{{Cite journal |last1=Tuya |first1=Fernando |last2=Asensio |first2=Maite |last3=Navarro |first3=Alberto |date=2020-05-01 |title="Urbanite" rays and sharks: Presence, habitat use and population structure in an urban semi-enclosed lagoon |url=https://www.sciencedirect.com/science/article/pii/S2352485520304709 |journal=Regional Studies in Marine Science |language=en |volume=37 |pages=101342 |doi=10.1016/j.rsma.2020.101342 |bibcode=2020RSMS...3701342T |hdl=10553/73658 |s2cid=225914133 |issn=2352-4855|hdl-access=free }}

Ecology

= Feeding and diet =

Benthic invertebrates form an important part of the common eagle ray's diet. The species largely feeds on crustaceans and bivalve molluscs that it excavates from the seabed. Other items in its diet include polychaete worms, gastropod molluscs, sea pens and small fish. Larger individuals consume more fish than smaller individuals. Instead of having pointed teeth, it has flattened hexagonal bars and plates arranged in a mosaic pattern on its jaws; with these, it crushes the shells of its prey.{{cite book |author1=Burton, Maurice |url=https://books.google.com/books?id=0gsPc5lk7_UC&pg=PA729 |title=International Wildlife Encyclopedia |author2=Burton, Robert |publisher=Marshall Cavendish |year=1969 |isbn=978-0-7614-7266-7 |pages=729–731}}

Mollusks and teleost fish were found to be the most important food items for individuals living in the Sea of Marmara, although polychaetas and crustaceans were also frequently found amongst the stomach contents.{{Cite journal |last1=Gül |first1=Güzin |last2=Demirel |first2=Nazli |date=2020 |title=Trophic interactions of uncommon batoid species in the Sea of Marmara |journal=J. Black Sea/Mediterranean Environment |volume=26 |issue=3 |pages=294–309}} Calliostoma lusitanicum and Stramonita haemastoma are the most common prey species off the coast off the Azores.{{Cite journal |last1=Ponte |first1=Dário Dinis Sousa |last2=Barcelos |first2=Luís Miguel Duarte |last3=Santos |first3=Cristina Sousa |last4=Medeiros |first4=João |last5=Barreiros |first5=João P. |date=2016 |title=Diet of Dasyatis pastinaca and Myliobatis aquila (Myliobatiformes) from the Azores, NE Atlantic |url=https://repositorio.uac.pt/handle/10400.3/4135 |journal=Cybium |volume=40 |issue=3 |pages=209–214 |issn=0399-0974}}

= Reproduction and development =

This species is known to gather in groups of dozens of individuals during the reproductive period.{{Cite journal |last1=Grancagnolo |first1=Desiree |last2=Arculeo |first2=Marco |date=2021 |title=Summer aggregation of common eagle ray, Myliobatis aquila (Chondrichthyes: Myliobatidae), in the Marine Protected Area of the Egadi Islands (southwestern Tyrrhenian Sea) |url=https://escholarship.org/uc/item/27p8p7xk |journal=Biogeographia: The Journal of Integrative Biogeography |language=en |volume=36 |doi=10.21426/B636051230 |s2cid=234245830 |issn=1594-7629|doi-access=free |hdl=10447/547067 |hdl-access=free }} Reproduction is oviviviparous. A clutch of three to seven young develop inside the mother, receiving nourishment at first from their egg yolks, but later from fluids secreted by their mother into her uterus. The gestation period is 6–8 months long, after which the female gives birth to between three and seven live pups.Whitehead, P.J.P., Bauchot, M.-L., Hureau, J. and Tortonese E. 1984. Fishes of the Northeastern Atlantic and the Mediterranean, Vol. I. UNESCO, Paris.Last, P., White, W., de Carvalho, M., Séret, B., Stehmann, M. and Naylor, G. 2016. Rays of the World. CSIRO Publishing, Clayton. The smallest juveniles were caught around France between May and September off the coast of France.Capapé, Christian & Guélorget, Olivier & Vergne, Yvan & Jean-pierre, Quignard. (2007). Reproductive biology of the common eagle ray, Myliobatis aquila (Chondrichthyes: Myliobatidae) from the coast cf Languedoc (Southern France, northern Mediterranean). Vie et Milieu. 53. 25–30. They still had a unhealed scar on the lower surface, suggesting they were neonates. A study conducted in South Africa in 1983 found juveniles in November.{{Cite journal |last1=Buxton |first1=C.D. |last2=Smale |first2=M.J. |last3=Wallace |first3=J.H. |last4=Cockcroft |first4=V.G. |date=1984-01-01 |title=Inshore small-mesh trawling survey of the Cape south coast. Part 4. Contributions to the biology of some teleostei and Chondrichthyes |journal=South African Journal of Zoology |volume=19 |issue=3 |pages=180–188 |doi=10.1080/02541858.1984.11447880 |issn=0254-1858|doi-access=free }} Juveniles were also found at Gran Canaria Island in October.

== Female development ==

Juvenile females have whitish membranous ovaries and thread-like oviducts. The oviducal glands are inconspicuous. Sub-adults have white translucent follicles and a well differentiated genital duct. The oviducal glands are slightly rounded. Adult females captured in January and March off the coast of France were found to have developing oocytes in both ovaries. The uteri were thick and muscular. They contained uterine fluid, which is probably sectreted from the villi that cover the internal wall. Females caught in August and September in the same region had between eight and ten yolky oocytes of a similar size and mass. Both uteri were enlarged and contained uterine fluid. The villi were well-developed and formed the trophonemata, which plays an important role in stingray gestation. Fertilised eggs surrounded by a diaphanous and a yellowish capsule that tapered to a small filament at either end were found in a female captured in October. The ovary contained atretic oocytes.

== Male development ==

Juvenile males have thread-like testes and genital ducts. The orbits have a smooth surface. Sub-adult males have no externally visible spermatocysts on the testes or sperm in the seminal vesicles. The superior surface of the orbit has a conspicuous protrusion. Adult males have elongated calcified claspers that are larger than the pelvic fins. The testes are well developed with visible external spermatocysts, a twisted genital duct and sperm in the seminal vesicles. They have well-developed conical supra-orbital vesicles.

== Hermaphrotism ==

At least one hermaphroditic specimen has been recorded. This specimen was classified as an abnormal hermaphrodite - one which is unable to perform as a functioning male or female as the reproductive organs were underdeveloped.{{Cite journal |last1=RAFRAFI-NOUIRA |first1=Sihem |last2=EL KAMEL-MOUTALIBI |first2=Olfa |last3=OUNIFI-BEN AMOR |first3=Khadija |last4=BEN AMOR |first4=Mohamed Mourad |last5=CAPAPÉ |first5=Christian |date=2017 |title=A Case of Hermaphroditism in the Common Eagle Ray Myliobatis Aquila (Chondrichthyes: Myliobatidae), Reported from the Tunisian Coast (Central Mediterranean) |url=https://doi.org/10.19233/ASHN.2017.06 |journal=Annales: Anali za istrske in mediteranske študije = annali di Studi istriani e mediterranei = annals for Istrian and Mediterranean studies. Series historia naturalis |issue=27–1 |doi=10.19233/ASHN.2017.06}}

= Parasites =

Several parasites live in and on this species. These include Entobdella diadema on the skin and Monocotyle myliobatis in the gills.{{Cite journal |last1=Llewellyn |first1=J. |last2=Euzet |first2=L. |date=May 1964 |title=Spermatophores in the Monogenean Entobdella diadema Monticelli from the skin of sting-rays, with a note on the taxonomy of the parasite |url=https://www.cambridge.org/core/journals/parasitology/article/abs/spermatophores-in-the-monogenean-entobdella-diadema-monticelli-from-the-skin-of-stingrays-with-a-note-on-the-taxonomy-of-the-parasite/FCFA3BFAF3FFDF3F65FD5984D6A160BC |journal=Parasitology |language=en |volume=54 |issue=2 |pages=337–344 |doi=10.1017/S0031182000067962 |s2cid=84808479 |issn=1469-8161}}{{Cite journal |last1=Tazerouti |first1=Fadila |last2=Neifar |first2=Lassad |last3=Euzet |first3=Louis |date=2011-01-01 |title=Redescription of Monocotyle myliobatis (Monogenea, Monocotylidae) from the type host Myliobatis aquila (Elasmobranchii, Myliobatidae) off the Algerian coast |journal=Acta Parasitologica |volume=56 |issue=3 |doi=10.2478/s11686-011-0056-4 |s2cid=25272145 |issn=1896-1851|doi-access=free }}

Relationship with humans

While it does contain venom, this species is not considered to pose a risk to humans as stings typically don't have any strong effects.{{Cite journal |last=Maretić |first=Z. |date=1982 |title=Elektrokardiografske promjene nakon ujeda i uboda otrovnih životinja |url=https://hrcak.srce.hr/clanak/233656 |journal=Arhiv za Higijenu Rada i Toksikologiju |language=en |volume=33 |issue=4 |pages=325–333 |issn=0004-1254}}

= Fishing =

This species is sometimes caught as bycatch, including in the pelagic trawl fishery. Due to declining numbers, the levels of bycatch are not nearly as high as they were historically.{{Cite journal |last=Quero |first=Jean-Claude |date=1998-01-01 |title=Changes in the Euro-Atlantic fish species composition resulting from fishing and ocean warming |journal=Italian Journal of Zoology |volume=65 |issue=sup1 |pages=493–499 |doi=10.1080/11250009809386873 |issn=1125-0003|doi-access=free }} A study in the Adriatic Sea showed that, on average, the fisheries in the region catch one common eagle ray every 20 hauls. About 79% of these are released alive after capture. The frequency is impacted by the depth of trawling, the season and the area being trawled. Most individuals were caught between April and September in the more northern areas at depths of {{Convert|20-40|m|ft|abbr=on}}.{{Cite journal |last1=Bonanomi |first1=Sara |last2=Pulcinella |first2=Jacopo |last3=Fortuna |first3=Caterina Maria |last4=Moro |first4=Fabrizio |last5=Sala |first5=Antonello |date=2018-01-29 |title=Elasmobranch bycatch in the Italian Adriatic pelagic trawl fishery |journal=PLOS ONE |language=en |volume=13 |issue=1 |pages=e0191647 |doi=10.1371/journal.pone.0191647 |issn=1932-6203 |pmc=5788366 |pmid=29377920 |bibcode=2018PLoSO..1391647B |doi-access=free }}

= Tourism =

This species has gained economic importance through underwater photographers and other SCUBA divers.

= Bioaccumulation =

A study in the Mediterranean Sea examined the mercury and methylmercury (the most common organic mercury compound) concentrations in three cartilaginous fish species. The common eagle ray was found to have lower mercury concentrations (0.67-1.01 mg/kg) than Chimaera monstrosa or Torpedo nobiliana. This is likely due to its diet as both the other two species feed on higher trophic levels (compared to the invertebrates that make up this eagle ray's diet). It also had the lowest methylmercury concentration (an average of 72%).{{Cite journal |last1=Storelli |first1=M.M |last2=Giacominelli-Stuffler |first2=R |last3=Marcotrigiano |first3=G.O |date=December 2002 |title=Total and methylmercury residues in cartilaginous fish from Mediterranean Sea |url=https://linkinghub.elsevier.com/retrieve/pii/S0025326X02002230 |journal=Marine Pollution Bulletin |language=en |volume=44 |issue=12 |pages=1354–1358 |doi=10.1016/S0025-326X(02)00223-0|pmid=12523539 |bibcode=2002MarPB..44.1354S }} This species does, however, appear to have higher levels of arsenic in its tissues than pelagic ray species.{{Cite journal |last1=Šlejkovec |first1=Zdenka |last2=Stajnko |first2=Anja |last3=Falnoga |first3=Ingrid |last4=Lipej |first4=Lovrenc |last5=Mazej |first5=Darja |last6=Horvat |first6=Milena |last7=Faganeli |first7=Jadran |date=2014 |title=Bioaccumulation of Arsenic Species in Rays from the Northern Adriatic Sea |journal=International Journal of Molecular Sciences |language=en |volume=15 |issue=12 |pages=22073–22091 |doi=10.3390/ijms151222073 |issn=1422-0067 |pmc=4284695 |pmid=25470025 |doi-access=free }}

Status

The International Union for Conservation of Nature to rate it as "critically endangered".

The taxonomic position of this fish is unclear as populations in the Mediterranean Sea may be a different species from those in the southeastern Atlantic. In the Gulf of Lion in the northwestern Mediterranean Sea, populations declined in the 1970s, and there and elsewhere in the Mediterranean, the fish is under threat from intensive fishing. The population has also been declining in the Atlantic Ocean off the coast of Europe, where it was once one of the most common skate and ray bycatch species (which collectively made up a total of about a quarter of the total catch by mass in 1881). The species is now rare in the region.

Along the coast of West Africa it is also the subject of artisanal fishing activities but these are less intensive and populations may be steady.