Environmental Biology of Fishes

, Volume 80, Issue 2–3, pp 221–237 | Cite as

Standardized diet compositions and trophic levels of skates (Chondrichthyes: Rajiformes: Rajoidei)

  • David A. Ebert
  • Joseph J. Bizzarro
Special Issue Skates


Skates by virtue of their abundance and widespread occurrence appear to play an influential role in the food webs of demersal marine communities. However, few quantitative dietary studies have been conducted on this elasmobranch group. Therefore, to better understand the ecological role of skates, standardized diet compositions and trophic level (TL) values were calculated from quantitative studies, and compared within and among skate and shark taxa. Prey items were grouped into 11 general categories to facilitate standardized diet composition and TL calculations. Trophic level values were calculated for 60 skate species with TL estimates ranging from 3.48 to 4.22 (mean TL = 3.80 ± 0.02 SE). Standardized diet composition results revealed that decapods and fishes were the main prey taxa of most skate species followed by amphipods and polychaetes. Correspondingly, cluster analysis of diet composition data revealed four major trophic guilds, each dominated by one of these prey groups. Fish and decapod guilds were dominant comprising 39 of 48 species analyzed. Analysis of skate families revealed that the Arhynchobatidae and Rajidae had similar TL values of 3.86 and 3.79 (t-test, P = 0.27), respectively. The Anacanthobatidae were represented by a single species, Cruriraja parcomaculata, with a TL of 3.53. Statistical comparison of TL values calculated for five genera (Bathyraja, Leucoraja, Raja, Rajella, Rhinoraja) revealed a significant difference between Bathyraja and Rajella (t-test, P = 0.03). A positive correlation was observed between TL and total length (L T) with larger skates (e.g. >100 cm L T) tending to have a higher calculated TL value (>3.9). Skates were found to occupy TLs similar to those of several co-occurring demersal shark families including the Scyliorhinidae, Squatinidae, and Triakidae. Results from this study support recent assertions that skates utilize similar resources to those of other upper trophic-level marine predators, e.g. seabirds, marine mammals, and sharks. These preliminary findings will hopefully encourage future research into the trophic relationships and ecological impact of these interesting and important demersal predators.


Skates Elasmobranchs Feeding ecology Prey composition Trophic guilds 



We thank Simon Brown, Pacific Shark Research Center (PSRC), Moss Landing Marine Laboratories (MLML), for his help in summarizing the articles used in this paper and inputting data, and Joan Parker and the library staff at MLML for their invaluable help in obtaining literature. Funding for this research was provided by NOAA/NMFS to the National Shark Research Consortium and PSRC, and in part by the National Sea Grant College Program of the U.S. Department of Commerce’s National Oceanic and Atmospheric Administration under NOAA Grant no. NA04OAR4170038, project number R/F-199, through the California Sea Grant College Program and in part by the California State Resources Agency.


  1. Ajayi TO (1982) Food and feeding habits of Raja Species (Batoidei) in Carmarthen Bay, Bristol Channel. J Mar Biol Assoc UK 62:215–223CrossRefGoogle Scholar
  2. Assis CA (1996) A generalized index for stomach contents analysis in fish. Sci Mar 60:385–389Google Scholar
  3. Beddington JR (1984) The response of multispecies systems to perturbations. In: May RM (ed) Exploitation of marine communities. Springer, Berlin, pp 209–225Google Scholar
  4. Bowen WD (1997) Role of marine mammals in aquatic ecosystems. Mar Ecol Prog Ser 158:267–274CrossRefGoogle Scholar
  5. Braccini JM, Perez JE (2005). Feeding habits of the sandskate Psammobatis extenta (Garman, 1913): sources of variation in dietary composition. Mar Freshw Res 56:395–403CrossRefGoogle Scholar
  6. Brickle P, Laptihovsky V, Pompert J, Bishop A (2003) Ontogenetic changes in the feeding habits and dietary overlap between three abundant rajid species on the Falkland Island’s shelf. J Mar Biol Assoc UK 83:1119–1125CrossRefGoogle Scholar
  7. Bulman C, Althaus F, He X, Bax NJ, Williams A (2001) Diets and trophic guilds of demersal fishes of the south-eastern Australian shelf. Mar Freshw Res 52:537–548CrossRefGoogle Scholar
  8. Capapé C (1975) Contribution a la biologie des Rajidae des cotes tunisiennes. 4. Raja clavata (Linne 1758): regime alimentaire. Ann Inst Michel Pacha 8:16–32Google Scholar
  9. Compagno LJV (1990) Alternate life history styles of cartilaginous fishes in time and space. Environ Biol Fish 28:33–75CrossRefGoogle Scholar
  10. Compagno LJV (2005) Checklist of living chondrichthyes. In: Hamlett WC (ed) Reproductive biology and phylogeny of Chondrichthyes: sharks, batoids, and chimaeras. Science Publishers, Inc., pp 501–548Google Scholar
  11. Compagno LJV, Ebert DA, Cowley PD (1991) Distribution of offshore demersal cartilaginous fishes (Class Chondrichthyes) off the west coast of southern Africa, with notes on their systematics. S Afr J Mar Sci 10:71–81Google Scholar
  12. Compagno LJV, Dando M, Fowler S (2005) A field guide to the sharks of the world. Harper-Collins, London, 416 ppGoogle Scholar
  13. Cortés E (1999) Standardized diet compositions and trophic levels in sharks. ICES J Mar Sci 56:707–717CrossRefGoogle Scholar
  14. Davenport SR, Bax NJ (2002) A trophic study of a marine ecosystem off southeastern Australia using stable isotopes of carbon and nitrogen. Can J Fish Aquat Sci 59:514–530CrossRefGoogle Scholar
  15. Ebert DA (2003) The sharks, rays and chimaeras of California. University California Press, Berkeley, California, USA, 285 ppGoogle Scholar
  16. Ebert DA, Cowley PD (2003) Diet, feeding behaviour and habitat utilization of the blue stingray Dasyatis chrysonota (Smith, 1828) in South African waters. Mar Freshw Res 54:957–965CrossRefGoogle Scholar
  17. Ebert DA, Compagno LJV (2007) Biodiversity and systematics of skates (Chondrichthyes: Rajiformes: Rajoidei). Environ Biol Fish (this volume)Google Scholar
  18. Ebert DA, Cowley PD, Compagno LJV (1991) A preliminary investigation of the feeding ecology of skates (Batoidea: Rajidae) off the west coast of southern Africa. S Afr J Mar Sci 10:71–81Google Scholar
  19. Ebert DA, Compagno LJV, Cowley PD (1992) A preliminary investigation of the feeding ecology of squaloid sharks off the west coast of southern Africa. S Afr J Mar Sci 12:601–609Google Scholar
  20. Ebert DA, Cowley PD, Compagno LJV (1996) A preliminary investigation of the feeding ecology of catsharks (Scyliorhinidae) off the west coast of southern Africa. S Afr J Mar Sci 17:233–240Google Scholar
  21. Ellis JR, Pawson MG, Shackley SE (1996) The comparative feeding ecology of six species of shark and four species of ray (Elasmobranchii) in the North-East Atlantic. J Mar Biol Assoc UK 76:89–106CrossRefGoogle Scholar
  22. Estrada JA, Rice AN, Lutcavage ME, Skomal GB (2003) Predicting trophic position in sharks of the north-west Atlantic Ocean using stable isotope analysis. J Mar Biol Assoc UK 83:1347–1350CrossRefGoogle Scholar
  23. Fauchauld K, Jumars PA (1979) The diet of worms: a study of polychaetes feeding guilds. Oceanogr Mar Biol Annu Rev 17:193–284Google Scholar
  24. Ferry LA, Cailliet GM (1996) Sample size sufficiency and data analysis: are we characterizing and comparing diet properly? In: MacKinlay D, Shearer K (eds) Feeding ecology and nutrition in fish: proceedings of the symposium on the feeding ecology and nutrition in fish. International Congress on the Biology of Fishes, San Francisco, CA, 14–18 July 1996, pp 71–80Google Scholar
  25. Fogarty MJ, Murawski SA (1998) Large-scale disturbance and the structure of marine systems: fishery impacts on Georges Bank. Ecol Appl 8:S6–S22CrossRefGoogle Scholar
  26. Gaichas S, Matta B, Stevenson D, Hoff J (2005) Bering Sea and Aleutian Islands skates. In: Stock assessment and fishery evaluation report for the groundfish resources of the Bering Sea/Aleutian Islands regions. North Pacific Fisheries Management Council, Anchorage, AK, Section 16.3:825–857Google Scholar
  27. Garrison LP (2000) Spatial and dietary overlap in the Georges Bank groundfish community. Can J Fish Aquat Sci 57:1679–1691CrossRefGoogle Scholar
  28. Garrison LP, Link JS (2000) Fishing effects on spatial distribution and trophic guild structure of the fish community in the Georges Bank region. ICES J Mar Sci 57:723–730CrossRefGoogle Scholar
  29. Gray AE, Mulligan TJ, Hannah RW (1997) Food habits, occurrence, and population structure of the bat ray, Myliobatis californica, in Humboldt Bay, California. Environ Biol Fish 49:227–238CrossRefGoogle Scholar
  30. Hobson KA (1993) Trophic relationships among high Arctic seabirds: insights from tissue-dependent stable-isotope models. Mar Ecol Prog Ser 95:7–18CrossRefGoogle Scholar
  31. Holden MJ, Tucker RN (1974) The food of Raja clavata Linnaeus 1758, Raja montagui Fowler 1910, Raja naevus Mϋller and Henle 1841, and Raja brachyura LaFont 1873 in British waters. J Cons Inst Explor Mer 35:189–193Google Scholar
  32. Hobson KA, Welch HE (1992) Determination of trophic relationships within a high Arctic marine food web using δ13C and δ15N analysis. Mar Ecol Prog Ser 84:9–18CrossRefGoogle Scholar
  33. Jennings S (2005) Size-based analyses of aquatic food webs. In: Belgrano A, Scharler UM, Dunne J, Ulanowicz RE (eds) Aquatic food webs. Oxford University Press, Oxford, pp 86–97CrossRefGoogle Scholar
  34. Lasiak TA (1982) Structural and functional aspects of the surf zone fish community in the Eastern Cape. PhD dissertation, University of Port Elizabeth, Port Elizabeth, South AfricaGoogle Scholar
  35. Last PR, Yearsley GK (2002) Zoogeography and relationships of Australasian skates (Chondrichthyes: Rajidae). J Biogeogr 29:1627–1641CrossRefGoogle Scholar
  36. Link JS, Garrison LP, Almeida FP (2002) Ecological interactions between elasmobranchs and groundfish species on the Northeastern U.S. Continental Shelf. I. Evaluating predation. N Am J Fish Manage 22:550–562 CrossRefGoogle Scholar
  37. Macpherson E, Roel BA (1987) Trophic relationships in the demersal fish community off Namibia. In: Payne AIL, Gulland JA, Brink KH (eds) The Benguela and comparable ecosystems. S Afr J Mar Sci 5:585–596Google Scholar
  38. Mayo RK, Fogarty MJ, Serchuk FM (1992) Aggregate fish biomass and yield on Georges Bank, 1960–87. J Northwest Atl Fish Sci 14:59–78CrossRefGoogle Scholar
  39. McEachran JD, Miyake T (1990) Zoogeography and bathymetry of skates (Chondrichthyes, Rajoidei). In: Pratt HL, Gruber SH, Taniuchi T (eds) Elasmobranchs as living resources: advances in the biology, ecology, systematics, and the status of the fisheries. NOAA Tech Rept 90, pp 305–326Google Scholar
  40. Mecklenberg CW, Mecklenberg TA, Thorsteinson LK (2002) Fishes of Alaska. American Fisheries Society, Bethesda, MD, USA, 1037 ppGoogle Scholar
  41. Menni RC, Stehmann MFW (2000) Distribution, environment, and biology of batoid fishes off Argentina, Uruguay, and Brazil. A review. Rev Mus Argentino Cienc Nat 2:69–109Google Scholar
  42. Mohan MV, Sankaran TM (1988) Two new indices for stomach content analysis of fishes. J Fish Biol 33:289–292CrossRefGoogle Scholar
  43. Morato T, Solà E, Grós MP (2003) Diets of thornback ray (Raja clavata) and tope shark (Galeorhinus galeus) in the bottom longline fishery of the Azores, northeastern Atlantic. Fish Bull 101:590–602Google Scholar
  44. Murawski SA (1991) Can we manage our multispecies fisheries? Fisheries 16:5–13CrossRefGoogle Scholar
  45. Muto EY, Soares LSH, Goitein R (2001) Food resource utilization of the skates Rioraja agassizii (Mϋller and Henle, 1841) and Psammobatis extenta (Garman, 1913) on the continental shelf off Ubatuba, south-eastern Brazil. Brazil J Biol 61:217–238Google Scholar
  46. Nyssen F, Brey T, Lepoint G, Bouquegneau JM, De Broyer C, Dauby P (2002) A stable isotope approach to the eastern Weddell Sea trophic web: focus on benthic amphipods. Polar Biol 25:280–287Google Scholar
  47. Orlov AM (1998) 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 Fish Res Bull 5:1–17Google Scholar
  48. Orlov AM (2003) Diets, feeding habits, and trophic relations of six deep-benthic skates (Rajidae) in the western Bering Sea. J Ichthyol Aquat Biol 7:45–59Google Scholar
  49. Orlov AM (2004) Trophic interrelationships in predatory fishes of Pacific waters circumambient the northern Kuril Islands and southeastern Kamchatka. Hydrobiol J 40:106–123CrossRefGoogle Scholar
  50. Pauly D, Christensen V (1995) Primary production required to sustain global fisheries. Nature 374:255–257CrossRefGoogle Scholar
  51. Pauly D, Trites AW, Capuli E, Christensen V (1998) Diet composition and trophic levels of marine mammals. ICES J Mar Sci 55:467–488CrossRefGoogle Scholar
  52. Pinkas LM, Oliphant S, Iverson ILK (1971) Food habits of albacore, bluefin tuna and Bonito in Californian waters. Calif Fish Game 152:1–105Google Scholar
  53. Quiniou L, Andriamirado GR (1979) Variations of the diet of three species of rays from Douarnenez Bay (Raja montagui Fowler, 1910; Raja brachyura Lafont, 1873; Raja clavata L., 1758). Cybium 3:27–39Google Scholar
  54. Robinson HJ, Cailliet GM, Ebert DA (2007) Food habits of the longnose skate, Raja rhina (Jordan and Gilbert, 1880), in central California waters. Environ Biol Fish (this volume)Google Scholar
  55. Rogers SI, Clarke KR, Reynolds JD (1999) The taxonomic distinctness of coastal bottom-dwelling fish communities of the North-east Atlantic. J Anim Ecol 68:769–782CrossRefGoogle Scholar
  56. Root RB (1967) The niche exploitation pattern of the blue-gray gnatcatcher. Ecol Monogr 37:317–350CrossRefGoogle Scholar
  57. Ross ST (1986) Resource partitioning in fish assemblages: a review of field studies. Copeia 2:352–368CrossRefGoogle Scholar
  58. Rossuow GJ (1983) The biology of the lesser sandshark. Rhinobatos annulatus in Algoa Bay with notes on other elasmobranchs. PhD dissertation, University of Port Elizabeth, Port Elizabeth, South Africa Google Scholar
  59. Sanger GA (1987) Trophic levels and trophic relationships of seabirds in the Gulf of Alaska. In: Croxall JP (ed) Seabirds: feeding ecology and role in marine ecosystems. Cambridge University Press, Cambridge, pp 229–257Google Scholar
  60. Smale MJ, Cowley PD (1992) The feeding ecology of skates (Batoidea: Rajidae) off the Cape South Coast, South Africa. S Afr J Mar Sci 12:823–834Google Scholar
  61. Smith JW, Merriner JV (1985) Food habits and feeding behavior of the cownose ray, Rhinoptera bonasus, in Lower Chesapeake Bay. Estuaries 8:305–310CrossRefGoogle Scholar
  62. Treloar MA, Stevens JD, Laurenson LJB (2007) Dietary comparisons of seven species of skates (Rajidae) in southeastern Australian waters. Environ Biol Fish (this volume)Google Scholar
  63. VanBlaircom GR (1982) Experimental analyses of structural regulation in a marine sand community exposed to oceanic swell. Ecol Monogr 52:283–305CrossRefGoogle Scholar
  64. Volger R, Milessi AC, Quinones RA (2003) Trophic ecology of Squatina guggenheim on the continental shelf off Uruguay and Northern Argentina. J Fish Biol 62:1254–1267CrossRefGoogle Scholar
  65. Yeon IJ, Hong SH, Cha HK, Kim ST (1999) Feeding habits of Raja pulchra in the Yellow Sea. Bull Nat’l Fish Res Dev Inst Korea 57:1–11Google Scholar
  66. Yoklavich MM, Greene HG, Cailliet GM, Sullivan DE, Lea RN, Love MS et al (2000) Habitat associations of deep-water rockfishes in a submarine canyon: an example of a natural refuge. Fish Bull 98:625–641Google Scholar

Copyright information

© Springer Science+Business Media, Inc. 2007

Authors and Affiliations

  1. 1.Pacific Shark Research CenterMoss Landing Marine LaboratoriesMoss LandingUSA

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