View source for Graytail skate

{{Short description|Species of cartilaginous fish}}
{{Speciesbox
| status = EN
| status_system = IUCN3.1
| status_ref = <ref name='iucn'>{{cite iucn |author=Pollom, R. |author2=Dulvy, N.K. |author3=Acuña, E. |author4=Bustamante, C. |author5=Chiaramonte, G.E. |author6=Cuevas, J.M. |author7=Herman, K. |author8=Paesch, L. |author9=Pompert, J. |author10=Velez-Zuazo, X. |year=2020 |title=''Bathyraja griseocauda'' |volume=2020 |page=e.T63113A124459226 |doi=10.2305/IUCN.UK.2020-3.RLTS.T63113A124459226.en |access-date=18 July 2024}}</ref>
| taxon = Bathyraja griseocauda
| authority = ([[John Roxborough Norman|Norman]], 1937)
| range_map = Greytail-skate-rangemap.png
| synonyms =  * ''Raja griseocauda'' <small>Norman, 1937</small>
}}
The '''graytail skate''' ('''''Bathyraja griseocauda'''''), or '''gray tail skate''', is a large [[species]] of [[Skate (fish)|skate]] in the family [[Arhynchobatidae]], native to the south-western Atlantic Ocean and south-eastern Pacific Ocean.  It is listed as [[endangered species|endangered]] by the [[IUCN]].<ref name='iucn'/> It was caught as part of a commercial fishery around the [[Falkland Islands]]<ref name='Wakeford'>{{cite journal | last = Wakeford | first = R.C. | others = D. J. Agnew, D. A. J. Middleton, J. H. W. Pompert and V. V. Laptikhovsky | title = Management of the Falkland Islands Multispecies Ray Fishery: Is Species-specific Management Required? | journal = Journal of Northwest Atlantic Fishery Science | year = 2004 | volume = 35 | pages = 309–324 | doi = 10.2960/J.v35.m497 | url = http://journal.nafo.int/35/wakeford/12-wakeford.pdf | access-date = 13 March 2012 | archive-url = https://web.archive.org/web/20140316165715/http://journal.nafo.int/35/wakeford/12-wakeford.pdf | archive-date = 16 March 2014 | url-status = dead | doi-access = free }}</ref> and is a bycatch in several other fisheries.
== Range and distribution ==
In the Atlantic Ocean, the graytail skate is found off the coast of [[Argentina]] and in the waters surrounding the Falkland Islands.  The northern extent of its range in the Atlantic is 37 degrees South.<ref name='iucn'/>  Its range extends very slightly past [[Cape Horn]] into the Pacific Ocean, off the coast of [[Chile]],<ref name='saez04'>{{cite journal | first1 = S. | last1 = Saez | first2 = J. | last2 = Lamilla | title = Sexual homodonty in ''Bathyraja griseocauda'' (Norman 1937) from the Southern Eastern Pacific (Chile) (Chondrichthyes, Rajidae: Arhynchobatinae) | journal = Journal of Applied Ichthyology | volume = 20 | pages = 189–193 | year = 2004 | issue = 3 | doi=10.1111/j.1439-0426.2004.00516.x| doi-access = free }}</ref> but does not extend beyond a northern extent of 41 degrees South.<ref name='iucn'/>
Although graytail skates have been found in waters as shallow as {{convert|51|m}},<ref name='fishbase'>{{FishBase | genus = Bathyraja | species = griseocauda | id = 27229 | month = March | year = 2012}}</ref> they are most often found deeper than {{convert|250|m}}.  They are found all over the continental shelf surrounding the Falkland Islands, but are found in highest concentration in the western, deeper shelf margin.<ref name='arkhipkin08'>{{cite journal | first = A.I. | last = Arkhipkin | others = N. Baumgartner, P. Brickle, V.V. Laptikhovsky, J.H.W. Pompert, and Z.N. Shcherbich | title = Biology of the skates ''Bathyraja brachyurops'' and ''B. griseocauda'' in waters around the Falkland Islands, Southwest Atlantic | journal = ICES Journal of Marine Science | year = 2008 | volume = 20 | issue = 4 | pages = 189–193 |doi=10.1093/icesjms/fsn015| doi-access =  }}</ref>
Individuals also segregate spatially by age class.  Nursery grounds near the Falkland Islands are generally located at depths of 300-350m.  Juveniles are found in deeper water, {{convert|400|to|600|m}}, but migrate either to the upper slope ({{convert|200|to|400|m}}) or into deeper water (below {{convert|600|m}}) after growing to {{convert|40|to|45|cm}} in length.<ref name='arkhipkin08'/>
The current population size of the graytail skate is not known.<ref name='iucn'/>  However the [[catch per unit effort]] has declined from 1993-2001,<ref name='Wakeford'/> as well as a decrease in size.<ref name='iucn'/>  These indicators led to the partial closure of the fishery around the Falklands, although no assessments have been completed to gauge current status. The frequency of bycatch and slow growth rate have led fisheries scientists to believe the fisheries restriction has not reversed the decline.<ref name='iucn'/>
== Biology and description ==
Recent reports indicate the graytail skate grows to a length of approximately {{convert|130|cm}}, with a maximum reported length of {{convert|157|cm}}.  The disc width is generally less than the total length, growing to a maximum width of approximately {{convert|90|cm}}.<ref name='arkhipkin08'/>  An earlier study found mature individuals to be considerably smaller.<ref name='Llano'>{{cite book | first1 = G.A. | last1 = Llano | first2 = I.E. | last2 = Wallen | title = Biology of the Antarctic Seas IV | year = 1971 | series = Antarctic Fisheries Series, vol 17 | publisher = American Geophysical Union: Washington D.C.}}</ref> The dorsal surface is black-brown and is covered by denticles but lacks spines.  The ventral surface is yellowish with dark spots near the tail.  The tail has 19-27 large spines.<ref name='Llano'/>
The graytail skate is a slow-growing species,<ref name='iucn'/> growing {{convert|4|to|6|cm}} per year.<ref name='arkhipkin08'/> This is slower than most species in the genus ''Bathyraja.''<ref name='iucn'/>  The maximum observed age is 28 years. Sexual maturity is reached at approximately 18 years for females and 14 years for males.<ref name='arkhipkin08'/>  The sex ratio is slightly skewed toward female.<ref name='arkhipkin08'/>
Like most skates, the graytail skate is [[oviparious]], laying paired eggs with horn-like projections.<ref name='fishbase'/>  It spawns year-round, although lays fewer eggs in the winter.<ref name='arkhipkin08'/>
Younger individuals eat primarily [[amphipods]] and other [[crustaceans]] and [[polychaete]] worms.  These disappear from the diet as the individual ages.  Older individuals eat rajids, ray-finned fish, and cephalopods.<ref name = 'brickle'>{{cite journal | first = P. | last = Brickle |author2=V. Laptikhovsky |author3=J. Pompert |author4=A. Bishop  | title = Ontogenetic changes in the feeding habits and dietary overlap between three abundant rajid species on the Falkland Islands' shelf | journal = Journal of the Marine Biological Association of the United Kingdom | year = 2003 | volume = 83 | issue = 5 | pages = 1119–1125 | doi=10.1017/s0025315403008373h| s2cid = 84601955 }}</ref>
=== Taxonomy ===
Initially classified in the genus ''[[Raja (fish)|Raja]]'', the graytail skate was reclassified as ''Bathyraja'' in 1971, a genus which did not exist in 1947.<ref name='Llano'/> This classification was supported by a morphological phylogenetic analysis<ref name='mceachran98'>{{cite journal | first1 = J.D. | last1 = McEachrun | first2 = K.A. | last2 = Dunn | title = Phylogenetic Analysis of Skates, a Morphologically Conservative Clade of Elasmobranchs (Chondrichthyes: Rajidae) | journal = Copeia | volume = 1998 | pages = 271–290 | year = 1998 | issue = 2 | doi=10.2307/1447424| jstor = 1447424 }}</ref> and genetically.  It is closely related to the [[Bathyraja papilionifera|butterfly skate]], ''Bathyraja papilionifera'', based on similarity of [[mtDNA]] fragments from [[Cytochrome c oxidase subunit I]].<ref name='barcode'>{{cite journal | first = E. | last = Mabragana | others = J. Martın Dıaz de Astarloa, R. Hanner, J. Zhang, and M. Gonzalez Castro | title = DNA Barcoding Identifies Argentine Fishes from Marine and Brackish Waters | journal = PLOS ONE | volume = 6 | pages = e28655 | year = 2011 | issue = 12 | doi=10.1371/journal.pone.0028655 | pmid=22174860 | pmc=3235135| bibcode = 2011PLoSO...628655M | doi-access = free }}</ref>
== Fisheries ==
The graytail skate was the largest component of the rajid catch in the Falkland Island from 1993 to 2001.  It comprised 24.2% of the harvest, followed by the [[white-dotted skate]], ''B. albomaculata'', and the [[broadnose skate]], ''B. brachyurops''.<ref name = 'Wakeford'/>  It is also a bycatch in trawler fisheries targeting [[teleosts]], and long line fisheries targeting [[patagonian toothfish]].<ref name='iucn'/>  Fisheries may be based in the Falkland Islands, Argentina, or Chile.
=== Management ===
The Falkland Islands instituted a management plan in 1994.  The plan identifies two mix-species fisheries, one north and one south of the Falklands.  Fishing for rajids in the north requires a license, while it has been prohibited in the south since 1996.  As of 2005, Argentina had not instituted an elasmobranch management plan.<ref name='fowler'>{{cite book | first = S.L. | last = Fowler | others = R.D. Cavanagh, M. Camhi, G.H. Burgess, G.M. Cailliet, S.V. Fordham, C.A. Simpfendorfer, and J.A. Musick | title = Sharks, Rays and Chimaeras: The Status of the Chondrichthyan Fishes | year = 2005 | publisher = IUCN – The World Conservation Union}}</ref>
==References ==
{{Reflist}}
{{Taxonbar|from=Q3758708}}
[[Category:Bathyraja]]
[[Category:Taxa named by John Roxborough Norman]]
[[Category:Fish described in 1937]]
[[Category:Fish of Argentina]]
[[Category:Fish of Chile]]
[[Category:Fauna of the Falkland Islands]]