Skates exhibit a variety of manifestations of sexual dimorphism. However, this phenomenon has been poorly documented in deepwater species. New data on the sexual dimorphism of five species of deepwater skates from the North Atlantic Ocean are presented: Amblyraja jenseni, Bathyraja pallida, Bathyraja richardsoni, Rajella bigelowi, and R. kukujevi. These skates exhibit sexual dimorphism most frequently in interorbital width, disc length and width, length of the third gill slit, horizontal diameter of the orbit, length of the fifth gill slit, space between the first and fifth gill slits, length of the second dorsal fin base, mouth width, length and width of each lobe of the nasal curtain, distance from the snout to the center of anus, distance from the snout tip to the point of maximum disc width, length of the lateral fold, length of the orbit + spiracle (measured together), tail height at the pelvic fin tips, and the number of median thorns. 1. Introduction Skates (Rajoidei) comprise an important component of shelf and continental slope benthic communities of the world’s oceans. They are major consumers of cephalopods, decapods, and fishes, often utilizing the same food resources as the apex predators, such as sea birds, marine mammals, and sharks [1]. Skates, like all chondrichthyan fishes, exhibit sexual dimorphism in the structure of the pelvic fins, which in males are modified to act as copulatory organs, or claspers [2]. Also, mature male skates have alar thorns on the edges of the disc, which help to grasp the female during copulation [3–5]. In many species sexual differences have been reported in length, body mass, size and age of sexual maturity, other external morphological features, and diet [3, 5–16]. Mature females and males of several skate species exhibit differences in the form and length of the teeth [3, 15, 17–23]. In one species, differences were observed in the shape and size of the shoulder and pelvic girdle [24]. Sexual differences in size and shape of the olfactory and electrical organs have also been found in some skates [3, 25–27]. Even with this variety of manifestations of sexual dimorphism in skates, the phenomenon has been poorly documented in deepwater species. This study presents new data on sexually dimorphic morphological characters of five deepwater skate species from the North Atlantic Ocean: Jensen's skate, Amblyraja jenseni [28]; pale ray, Bathyraja pallida [29]; Richardson's ray, Bathyraja richardsoni [30]; Bigelow's ray, Rajella bigelowi [31]; Mid-Atlantic skate, R. kukujevi [32]. 2. Materials and Methods Our
References
[1]
D. A. Ebert and J. J. Bizzarro, “Standardized diet compositions and trophic levels of skates (Chondrichthyes: Rajiformes: Rajoidei),” Environmental Biology of Fishes, vol. 80, no. 2-3, pp. 221–237, 2007.
[2]
N. N. Gurtovoj, B. S. Matveev, and F. Ya. Dzerzhinskij, Practical Zootomy of Vertebrates (Lower Chordates, Agnatha, Fish). Handbook for Biological Specialities of Universities, Vysshaya Shkola, Moscow, Russia, 1976.
[3]
R. Ishiyama, “Studies on the rajid fishes (Rajidae) found in the waters around Japan,” Journal of the Shimonoseki College of Fisheries, vol. 7, pp. 191–394, 1958.
[4]
T. C. Tricas, “Courtship and mating-related behaviors in myliobatid rays,” Copeia, vol. 3, pp. 553–556, 1980.
[5]
J. M. Braccini and G. E. Chiaramonte, “Biology of the skate Psammobatis extenta (Garman, 1913) (Batoidea: Rajidae),” Revista Chilena de Historia Natural, vol. 75, no. 1, pp. 179–188, 2002 (Spanish).
[6]
I. Jardas, “The morphometry and population diagnostic of thornback ray, Raja clavata L., in the Adriatic,” Acta Adriatica, vol. 17, pp. 1–26, 1975.
[7]
P. B. O. Ochumba, “The distribution of skates and rays along the Kenyan coast,” Journal of East African Natural History, vol. 78, pp. 26–52, 1988.
[8]
C. Capape, J. L. Bouchereau, and J. A. Tomasini, “Occurrence of the devil ray Mobula mobular Bonnaterre, 1788) (pisces, rajiformes, mobulidae) in the Gulf of Aigues-Mortes. Anatomy of pelvic girdle and claspers,” Mésogée, vol. 50, pp. 9–14, 1990 (French).
[9]
A. M. Orlov, “On feeding of mass species of deep-sea skates (Bathyraja spp., Rajidae) from the Pacific waters of the northern Kurils and southeastern Kamchatka,” Journal of Ichthyolo, vol. 38, pp. 635–644, 1998.
[10]
A. M. Orlov, “The diets and feeding habits of some deep-water benthic skates (Rajidae) in the Pacific waters off the northern Kuril Islands and southeastern Kamchatka,” Alaska Fishery Research Bulletin, vol. 5, pp. 1–17, 1998.
[11]
A. M. Orlov, “Diets, feeding habits, and trophic relations of six deep-benthic skates (Rajidae) in the western Bering Sea,” Aqua Journal of Ichthyology and Aquatic Biology, vol. 7, pp. 45–60, 2003.
[12]
Z. S. Almedia, J. S. Nunes, C. L. Costa, et al., “Report of Urotrigon microphthalmum (Elasmobranchii: Urolophidae) from Maranhao (Brazil)'s shallow waters and notes about its biology,” Boletin de Investigaciones Marinas y Costeras, vol. 29, pp. 67–72, 2000 (Portuguese).
[13]
T. Gedamke, W. D. DuPaul, and J. A. Musick, “Observations on the life history of the barndoor skate, Dipturus laevis, on Georges Bank (Western North Atlantic),” Journal of Northwest Atlantic Fishery Science, vol. 35, pp. 67–78, 2005.
[14]
J. M. Braccini and G. E. Chiaramonte, “Intraspecific variation in the external morphology of the sand skate,” Journal of Fish Biology, vol. 62, no. 4, pp. 959–972, 2002.
[15]
L. B. Scenna, Distribution, abundance and some biological aspects of the Patagonian skate Bathyraja macloviana (Rajidae) from the continental shelf off Argentina and Uruguay, M.S. thesis, Universidad Nacional de Mar del Plata, Mar Del Plata, Argentina, 2003.
[16]
N. L. Ruocco, L. O. Lucifora, J. M. Diaz de Astarloa, and O. W？hler, “Reproductive biology and abundance of the white-dotted skate, Bathyraja albomaculata, in the Southwest Atlantic,” ICES Journal of Marine Science, vol. 63, no. 1, pp. 105–116, 2006.
[17]
A. Feduccia and H. Slaughter, “Sexual dimorphism in skates (Rajidae) and its possible role in differential niche utilization,” Evolution, vol. 28, pp. 164–168, 1974.
[18]
J. D. McEachran, “Reply to ‘sexual dimorphism in skates (Rajidae)’,” Evolution, vol. 31, pp. 218–220, 1977.
[19]
R. M. McCourt and A. N. Kerstitch, “Mating behavior and sexual dimorphism in dentition in the stingray Urolophus concentricus from the Gulf of California,” Copeia, vol. 4, pp. 990–991, 1980.
[20]
S. M. Kajiura and T. C. Tricas, “Seasonal dynamics of dental sexual dimorphism in the atlantic stingray Dasyatis sabina,” Journal of Experimental Biology, vol. 199, no. 10, pp. 2297–2306, 1996.
[21]
S. E. Nordell, “Obervations of the mating behavior and dentition of the round stingray, Urolophus halleri,” Environmental Biology of Fishes, vol. 39, no. 3, pp. 219–229, 2005.
[22]
T. Gedamke, Developing a stock assessment for the barndoor skate (Dipturus laevis) in the northeast United States, Ph.D. thesis, Virginia Institute of Marine Science, Virginia, Va, USA, 2006.
[23]
L. B. Scenna, S. B. Garsia de la Rosa, and J. M. Diaz de Astarloa, “Trophic ecology of the Patagonian skate, Bathyraja macloviana, on the Argentine continental shelf,” ICES Journal of Marine Science, vol. 63, no. 5, pp. 867–874, 2006.
[24]
M. Stehmann, “Breviraja caerulea spec. nov. (Elasmobranchii, Batoidea, Rajidae); a new deepwater skate and the first record of the genus in the North East Atlantic,” Archiv für Fischereiwissenschaft, vol. 27, pp. 97–114, 1976.
[25]
S. Waghray, “Olfactory organ and its sexual dimorphism in the electric ray, Narcine timlei (Day),” Indian Journal of Fisheries, vol. 32, pp. 148–151, 1985.
[26]
G. Pequeno, R. Navarro, and G. Oporto, “Discopyge tschudii Heckel, 1845: contribution to its taxonomy with emphasis on its sexual dimorphism (Chondrichthyes, Narcinidae),” Estudios Oceanologicos, vol. 7, pp. 41–50, 1988 (Spanish).
[27]
J. M. Morson and J. F. Morrissey, “Morphological variation in the electric organ of the little skate (Leucoraja erinacea) and its possible role in communication during courtship,” Environmental Biology of Fishes, vol. 80, no. 2-3, pp. 267–275, 2007.
[28]
H. B. Bigelow and W. C. Schroeder, “New and little known cartilaginous fishes from the Atlantic,” Bulletin of the Museum of Comparative Zoology, vol. 103, pp. 385–408, 1950.
[29]
G. R. Forster, “A new deep-sea ray from the bay of Biscay,” Journal of the Marine Biological, vol. 47, pp. 281–286, 1967.
[30]
J. A. F. Garrick, “Studies on New Zealand Elasmobranchii. Part XIII. A new species of Raja from 1,300 fathoms,” Transactions of the Royal Society of New Zealand, vol. 88, pp. 743–748, 1961.
[31]
M. Stehmann, “Raja “bathyphila”, a composite species of the subgenus Rajella: redescription of R. bathyphila Holt and Byrne, 1908 and Raja bigelowi spec. nov. (pisces, rajiformes, rajidae),” Archiv für Fischereiwissenschaft, vol. 29, pp. 23–58, 1978.
[32]
V. N. Dolganov, “Raja (Rajella) kukujevi sp.n. (Elasmobranchii, Rajidae)—new skate species from the Mid-Atlantic Ridge,” Zoologicheskii Zhurnal, vol. 64, pp. 304–307, 1985 (Russian).
[33]
M. Stehmann, “First and new records of skates (Chondrichthyes, Rajiformes, Rajidae) from the West African continental slope (Morocco to South Africa), with descriptions of two new species,” Archive of Fishery and Marine Research, vol. 43, pp. 1–119, 1995.
[34]
M. F. W. Stehmann and N. R. Merrett, “First records of advanced embryos and egg capsules of Bathyraja skates from the deep north-eastern Atlantic,” Journal of Fish Biology, vol. 59, no. 2, pp. 338–349, 2001.
[35]
A. Orlov, C. Cotton, and I. Byrkjedal, “Deepwater skates (Rajidae) collected during the 2004 cruises of R.V. “G.O. Sars” and M.S. “Loran” in the Mid-Atlantic Ridge area,” Cybium, vol. 30, no. 4, pp. 35–48, 2006.
[36]
H. B. Bigelow and W. C. Schroeder, “Sawfishes, guitarfishes, skates and rays,” in Fishes of the Western North Atlantic, Part 2, J. Tee-Van, C. M. Breder, A. E. Parr, W. C. Schroeder, and L. P. Schultz, Eds., pp. 1–514, Yale University, New Haven, Conn, USA, 1953.
[37]
C. L. Hubbs and R. Ishiyama, “Methods for taxonomic study and description of skates (Rajidae),” Copeia, vol. 3, pp. 483–491, 1968.
[38]
M. Stehmann, “Results of the research cruises of FRV Walther Herwig to South America. LXIV. Bathyraja papilionifera spec. nov. (Pisces, Batoidea, Rajidae), another new skate from the western South Atlantic from the continental slope off northern Argentina,” Archiv für Fischereiwissenschaft, vol. 36, pp. 195–211, 1985.
[39]
H. B. Bigelow and W. C. Schroeder, “Notes on Northwest Atlantic sharks and skates,” Bulletin of the Museum of Comparative Zoology, vol. 68, pp. 237–251, 1927.
[40]
G. R. Forster, “Raja richardsoni from the continental slope off south-west England,” Journal of the Marine Biological Association of the United Kingdom, vol. 45, pp. 773–777, 1965.
[41]
A. E. Leviton and R. H. Gibbs, “Standards in herpetology and ichthyology. Standard symbolic codes for institutional resource collections in herpetology and ichthyology,” Copeia, vol. 1, supplement 1, pp. 280–282, 1988.
[42]
A. E. Leviton, R. H. Gibbs, E. Heal, and C. E. Dawson, “Standards in herpetology and ichthyology: part 1. Standard symbolic codes for institutional resource collections in herpetology and ichthyology,” Copeia, vol. 3, pp. 802–832, 1985.
[43]
A. H. Leim and W. B. Scott, “Fishes of the Atlantic coast of Canada,” Bulletin of the Fisheries Research Board of Canada, vol. 155, pp. 1–485, 1966.
[44]
J. D. M. Gordon and J. A. R. Duncan, “Deep-sea bottom-living fishes at two repeat stations at 2,200 and 2,900？m in the Rockall Trough, northeastern Atlantic Ocean,” Marine Biology, vol. 96, no. 3, pp. 309–325, 1987.
[45]
J. D. M. Gordon and J. A. R. Duncan, “A note on the distribution and diet of deep-water rays (Rajidae) in an area of the Rockall Trough,” Journal of the Marine Biological Association of the United Kingdom, vol. 69, no. 3, pp. 655–658, 1989.
[46]
J. C. Quero, P. Lorance, J. Tardy, and E. Tardy, “Ichthyologic observations in 1999 on board research vessel Thalassa,” Annales de la Société des Sciences Naturelles de la Charente-Maritime, vol. 8, pp. 1047–1058, 2000 (French).
[47]
G. R. Forster, “Line-fishing on the continental slope. II,” Journal of the Marine Biological Association of the United Kingdom, vol. 48, pp. 479–483, 1968.
[48]
J. A. Moore, K. E. Hartel, J. E. Craddock, and J. K. Galbraith, “An annotated list of deepwater fishes from off the New England region, with new area records,” Northeastern Naturalist, vol. 10, no. 2, pp. 159–248, 2003.
[49]
M. Stehmann and D. L. Bürkel, “Rajidae,” in Fishes of the North-eastern Atlantic and the Mediterranean, P. J. P. Whitehead, M.-L. Bauchot, J.-C. Hureau, J. Nielsen, and E. Tortonese, Eds., vol. 1, pp. 163–196, UNESCO, Paris, France, 1984.
[50]
M. W. Clarke, “Records of deep water chondrichthyan fish caught on long-line in the Rockall Trough,” Journal of the Marine Biological Association of the United Kingdom, vol. 80, no. 2, pp. 377–378, 2000.
[51]
W. Templeman, “The skate, Raja richardsoni Garrick, 1961, assigned to Bathyraja,” Journal of the Fisheries Research Board of Canada, vol. 30, pp. 1729–1732, 1973.
[52]
W. Templeman, “First records, description, distribution, and notes on the biology of Bathyraja richardsoni (Garrick) from the Northwest Atlantic,” Journal of the Fisheries Research Board of Canada, vol. 30, pp. 1831–1840, 1973.
[53]
S. P. Iglesias, “Chondrichthyans from the Northeastern Atlantic and the Mediterranean (a natural classification based on collection specimens),” 2006, http://www.mnhn.fr/iccanam/.
