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information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Common Skate (Dipturus batis)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.

Summary

Description

A large ray with a long pointed snout. Males growing up to 2 m in length, while females may reach up to 3 m in length. The leading edge of the wings is slightly concave and the small dorsal fins near the tip of the tail almost touch. The young have large thorns near the eyes and one row of thorns along the back of the tail, while older specimens lack the thorns near the eyes but have two rows of along the tail. The upper (dorsal) side is brownish-green with lighter spots and the underside dark grey, sometimes with black stripes, spots or marbling. Immature skate under 40lb in weight are jet black underneath which fades to grey as they get larger (Davy Holt, pers. comm.).

Recorded distribution in Britain and Ireland

Populations of Dipturus batis are found off the coasts of Isles of Scilly, western British Channel, west and north Ireland and west Scotland.

Global distribution

Atlantic coasts from Madeira and northern Morocco northward to Iceland including the North Sea. Also in western parts of the Baltic and western and northern Mediterranean.

Habitat

The skate lives on sandy and muddy bottoms. The adults live in depths of 10 to 600 m while younger specimens prefer shallower waters.

Depth range

down to 600 m

Identifying features

  • Up to 3 m in length.
  • Long, pointed snout.
  • Juveniles have large thorns near their eyes and one row of thorns along the back of tail.
  • Adults lack the eye thorns but have two rows of thorns along the tail.
  • Dorsal surface is brownish green with lighter spots, the underside is dark grey, sometimes with spots, stripes or marbling.

Additional information

Following a report in recent taxonomic literature, this species now belongs to the genus Dipturus, although may still be referred to as Raja in some texts, (see McEachran & Dunn, 1988).

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Biology review

Taxonomy

PhylumChordata
ClassElasmobranchii
OrderRajiformes
FamilyRajidae
GenusDipturus
Authority(Linnaeus, 1758)
Recent SynonymsRaja batis (Linnaeus, 1758)

Biology

Typical abundance
Male size range22 - 200cm
Male size at maturity150cm
Female size range180cm
Female size at maturity
Growth formPisciform
Growth rate0.9 - 14kg/year
Body flexibilityNot relevant
Mobility
Characteristic feeding methodPredator
Diet/food source
Typically feeds onBristle worms, sand eels, crabs and flatfish
Sociability
Environmental positionDemersal
DependencyNo text entered.
SupportsHost

the copepod Acanthochondrites annulatus which attaches to the gills of the skate.

Is the species harmful?No

Biology information

The growth rate listed above may seem quite rapid but if weight at maturity is taken into consideration, 54 kg for males (Muus & Dahlstrom, 1974) and 94 kg for females (Walker & Hislop 1998) it can be seen that it takes many years to reach maturity. The data for growth rate came from tag and release studies off the west coast of Scotland (Sutcliffe, 1994; Little, 1995, 1998) by comparing weight change of skate between captures. Skates seem to have a start-and-stop growth pattern, where they have rapid growth for a short period and then remain at that weight for some time with no growth until they have another episode of rapid growth (Sutcliffe, 1994).

Habitat preferences

Physiographic preferencesOpen coast, Offshore seabed
Biological zone preferencesLower circalittoral, Lower infralittoral, Upper circalittoral, Upper infralittoral
Substratum / habitat preferencesCoarse clean sand, Fine clean sand, Mixed, Mud, Muddy gravel, Muddy sand, Sandy mud
Tidal strength preferencesModerately Strong 1 to 3 knots (0.5-1.5 m/sec.), Strong 3 to 6 knots (1.5-3 m/sec.), Very Weak (negligible), Weak < 1 knot (<0.5 m/sec.)
Wave exposure preferencesExposed, Moderately exposed, Sheltered, Very exposed, Very sheltered
Salinity preferencesFull (30-40 psu)
Depth rangedown to 600 m
Other preferencesNone known
Migration PatternNon-migratory / resident

Habitat Information

Dipturus batis was found around all British and Irish coasts except the south east. However, it has disappeared from much of its former range due to fishing pressure (Brander, 1981, Walker & Hislop, 1998; Jennings et al., 1999; Rogers & Ellis, 2000). Remnant populations occur in areas unsuitable for commercial fishing (Shark Trust pers. comm.).

Life history

Adult characteristics

Reproductive typeGonochoristic (dioecious)
Reproductive frequency See additional information
Fecundity (number of eggs)11-100
Generation time10-20 years
Age at maturity11 years
SeasonInsufficient information
Life span20-100 years

Larval characteristics

Larval/propagule type-
Larval/juvenile development Oviparous
Duration of larval stageNot relevant
Larval dispersal potential No information
Larval settlement periodNot relevant

Life history information

Females breed every other year (Little, 1997) and produce up to 40 eggs (Walker & Hislop, 1998) which are laid in the spring and summer (Whitehead et al., 1984). The egg case is large, 15-25 cm long and 8-15 cm wide (Dipper, 2001). It is rectangular and similar to 'mermaids purses' that are often found on the strandline. Eggcases are laid on the seabed and have been reported as being 'loose' on the seabed and perhaps very vaguely 'wedged' in between rocks (Paul Kay, pers. comm.). The young hatch after 2-5 months (depending on temperature) (Muus & Dahlstrom, 1974) at about 22 cm in length (Brander, 1981).
Dipturus batis is vulnerable to overfishing because of its slow growth, late maturity and low fecundity (Brander, 1981; Jennings et al, 1999). Only about 40 eggs are laid every other year and each generation takes 11 years to reach maturity, therefore populations cannot recover quickly from large mortalities. It has been estimated that a mortality of greater than 38% per year will lead to continual decline in the population and recovery is unlikely to occur until mortality is relaxed (Walker & Hislop, 1998). Numbers of common skate caught in trawls began to decline in the 1920s and again in the 1950s after a recovery period during the second World War and disappeared from the North Sea between the mid 1950s and early 1980s (Walker & Hislop, 1998). However, it has been shown that Dipturus batis can survive being trawled if it is released after capture (Little, 1995) . Dipturus batis was recorded as 'not uncommon in trawls' in the Marine fauna of the Isle of Man (Bruce et al., 1963) and was regarded as a common species by Hureau & Monod (1979). However the common skate had become all but extinct by the late 1970s (Brander, 1981). Similarly, between 1901 and 1907, the common skate made up 4% of all elasmobranchs caught in trawls in southwest England but between 1989 and 1997 none were caught (Rogers & Ellis, 2000).
A tag and recapture program has been implemented in northeastern Scotland. Of 147 recaptured individuals, only 5 had travelled more than 20 km (Little, 1998), which suggests that Dipturus batis is vulnerable to local extinction by fishing with little chance of re-population from adjacent areas.

Sensitivity reviewHow is sensitivity assessed?

Physical pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
Low High Low Very low
As Dipturus batis is highly motile, it would move away from an area that lost a suitable substratum and return when the area was back to normal. A certain amount of stress maybe caused by loss of food items with the substratum and because of the need to find new foraging/spawning areas. Therefore an intolerance of low has been recorded. Recoverability is likely to be high, resulting in a sensitivity assessment of low. Substrate removal is likely to destroy egg cases, but the location of important breeding and nursery grounds is poorly understood.
Low High Low Very low
Dipturus batis would move away from an area that was being smothered but with some stress due to loss of food and energetic costs of migrating to new foraging areas. Therefore an intolerance of low has been recorded. Recoverability is likely to be high, resulting in a sensitivity assessment of low. Egg cases on the sea bed are likely to be more sensitive.
Not relevant Not relevant Not relevant Not relevant
It is not known whether an increase in suspended sediment will have an effect on Dipturus batis. Not relevant has been recorded because the skate is mobile enough to avoid local adverse effects.
Not relevant Not relevant Not relevant Not relevant
It is not known whether an decrease in suspended sediment will have an effect on Dipturus batis. Not relevant has been recorded because the skate is mobile enough to avoid local adverse effects.
Not relevant Not relevant Not relevant Not relevant
Dipturus batis is a sublittoral species unlikely to be subject to exposure to air. Therefore desiccation is not relevant.
Not relevant Not relevant Not relevant Not relevant
Dipturus batis is a sublittoral species unlikely to be subject to exposure to air. Therefore an increase in emergence is not relevant.
Not relevant Not relevant Not relevant Not relevant
Dipturus batis is a sublittoral species unlikely to be subject to exposure to air. Therefore a decrease in emergence is not relevant.
Low High Low Low
Dipturus batis has been recorded from sites around the UK with varying hydrodynamic conditions (see adult distribution) and therefore is unlikely to be affected by changes in flow rate (JNCC, 1999).
Low High Low Not relevant
Dipturus batis has been recorded from sites around the UK with varying hydrodynamic conditions (see adult distribution) and therefore is unlikely to be affected by changes in flow rate (JNCC, 1999).
Intermediate Moderate Moderate Very low
Sudden changes in temperature are unlikely to affect adults because they can move away but developing young may be affected. A study on a related species, Raja eglanteria, found that the embryos of this species do not develop at temperatures over 24 °C (Whitehead et al., 1984). As such intolerance is assessed as intermediate. Chronic changes in temperature would also have little effect as the adults experience large temperature changes when moving between deep and shallow water. In addition, the world distribution of Dipturus batis is from the coasts of north-western Africa to the North coast of Norway so it is unlikely to experience temperatures outside of its tolerance range in British and Irish waters. Therefore recoverability of adults is likely to be high, however due to a lack of information on the effects on developing young, recoverability is assessed as moderate, resulting in a moderate sensitivity rating.
Intermediate Moderate Moderate
Sudden changes in temperature are unlikely to affect adults because they can move away but developing young may be affected. As such intolerance is assessed as intermediate. Chronic changes in temperature would have little effect as the adults experience large temperature changes when moving between deep and shallow water. In addition, the world distribution of Dipturus batis is from the coasts of north-western Africa to the North coast of Norway so it is unlikely to experience temperatures outside of its tolerance range in British and Irish waters. Therefore recoverability of adults is likely to be high, however due to a deficit of information on the effects on developing young, recoverability is assessed as moderate, resulting in a moderate sensitivity rating.
Tolerant Not relevant Not sensitive Very low
An increase in turbidity could potentially interfere with foraging by inhibiting visual location of prey. However, Dipturus batis is a bottom feeder that is probably adapted to murky, silty water and utilize smell and electromagnetic cues to locate prey. Therefore the species is considered tolerant, and not sensitive has been recorded.
Tolerant Not relevant Not sensitive
A decrease in turbidity may aid predators. However, since man is the main threat to Dipturus batis, a decrease in turbidity is unlikely to increase the predation rate on this species. A decrease in turbidity may however, influence foraging success, either because prey gain an earlier warning of the skates' approach or because the skates' visual acquisition of prey is improved. Therefore the species is considered tolerant, and not sensitive has been recorded.
Tolerant Not relevant Not sensitive Low
Dipturus batis has been recorded at sites all over the UK which vary from very sheltered to very exposed (see adult distribution) and anyway can swim to deeper areas if wave action increases to the extent that oscillatory movements on the seabed become excessive. As a result Dipturus batis is unlikely to be affected by an increase or decrease in wave exposure, so is considered tolerant, and not sensitive has been recorded.
Tolerant Not relevant Not sensitive Low
Dipturus batis has been recorded at sites all over the UK which vary from very sheltered to very exposed (see adult distribution). Therefore the species is unlikely to be affected by an increase or decrease in wave exposure, so is considered tolerant, and not sensitive has been recorded.
Tolerant Not relevant Not sensitive Not relevant
Fish with swimbladders have been reported to be the most sensitive to noise (Vella et al., 2001). Dipturus batis is an elasmobranch and therefore does not have a swimbladder so is among the fish that are less sensitive to noise. However, sudden loud noises of low frequency have been shown to elicit an avoidance response in most fish (Vella et al. 2001). Noise rarely has a physiological affect on fish so Dipturus batis has been deemed tolerant, and therefore not sensitive to noise.
Low Immediate Not sensitive Very low
Adult Dipturus batis can be found at depths from the shallow sublittoral down to 600 m so are unlikely to be disturbed by boats or divers, although divers might disturb young skate in shallow water. Recoverability is likely to be immediate, however, since the skate can swim away from the disturbance and return when it has gone. Therefore an intolerance of low has been recorded, and the species is deemed not sensitive.
Intermediate Moderate Moderate Very low
Dipturus batis has a high resilience when trawled or caught by rod and line and then released again (Little, 1995). Therefore adults are probably tolerant of abrasion and physical disturbance at the benchmark level. Because of the shape of rays, they cannot escape trawl nets once they have been captured. A newborn skate is about 22 cm long and almost as wide, therefore is unable to pass through the mesh of fishing nets. Because of their small size there is a greater chance a juvenile skate will be damaged in a net than an adult skate. This could lead to high mortality/stress in the juveniles and affect the processes maintaining the population. Therefore an intolerance of intermediate has been recorded. Recoverability is probably moderate (see information below) hence sensitivity is assessed as moderate.
Low High Low Very low
Dipturus batis has a high resilience when trawled or caught by rod and line and then released again (Little, 1995). In addition, this species is found on a variety of substrata all around the UK and therefore is probably quite tolerant of displacement. Recoverability is likely to be high, resulting in a low sensitivity recording.

Chemical pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
No information Not relevant No information Not relevant
No information found.
Heavy metal contamination
No information Not relevant No information Very low
General information on the tolerance of fish to metal contamination reveals that part per billion concentrations are not lethal but may reduce gill activity, growth and hatching success of eggs. Copper was reported to be the most toxic of metals and suppressed egg hatching at concentrations of 10 parts per billion in certain teleost fish (Bryan, 1984). The leathery egg case of rays may make them less susceptible to metal contamination. However, in the absence of evidence on the effects in Dipturus batis no assessment can be made.
Hydrocarbon contamination
No information Not relevant No information Not relevant
No information found.
Radionuclide contamination
No information Not relevant No information Not relevant
No information found.
Changes in nutrient levels
No information Not relevant No information Not relevant
No information was found on the effect of nutrient enrichment or algal blooms was found.
Low High Low Very low
As with many of the other factors, the high motility of this species allows it to escape adverse changes in salinity. Therefore intolerance is recorded as low and recoverability is likely to be high, resulting in a sensitivity assessment of low.
Low High Low
As with many of the other factors, the high motility of this species allows it to escape adverse changes in salinity. Therefore intolerance is recorded as low and recoverability is likely to be high, resulting in a sensitivity assessment of low.
No information Not relevant No information Not relevant
No information was found on the effects of hypoxia on Dipturus batis.

Biological pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
No information Not relevant No information Not relevant
No information found.
No information Not relevant No information Not relevant
No non-native species are known to compete with the common skate.
High Low High High
The slow growth rate, late maturity and low fecundity make Dipturus batis vulnerable to overfishing and it has disappeared from much of its former range due to fishing pressure (Brander; 1981; Walker & Hislop, 1998; Jennings et al. 1999; Rogers & Ellis, 2000). Only about 40 eggs are laid every other year and each generation takes 11 years to reach maturity, therefore populations cannot recover quickly from large mortalities. It has been estimated that a mortality of greater than 38% per year will lead to continual decline in the population and recovery is unlikely to occur until mortality is relaxed (Walker & Hislop, 1998). Numbers of common skate caught in trawls began to decline in the 1920s and again in the 1950s after a recovery period during the second world war and disappeared from the North Sea between the mid 1950s and early 1980s (Walker & Hislop, 1998). Dipturus batis was recorded as 'not uncommon in trawls' in the Marine fauna of the Isle of Man (Bruce et al., 1963) and was regarded as a common species by Hureau & Monod (1979). However the common skate had become all but extinct by the late 1970s due to overfishing (Brander, 1981). Similarly, between 1901 and 1907, the common skate made up 4% of all elasmobranchs caught in trawls in southwest England but between 1989 and 1997 none were caught (Rogers & Ellis, 2000). Therefore an intolerance of high and a recoverability of low has been recorded. The species is highly sensitive to this factor.
Low No information No information Low
Dipturus batis feeds on flatfish and some of the larger individuals take cod, haddock and herring (Dipper, 2001), and fishing pressure on these species may affect the skates food supply. Therefore an intolerance of low has been recorded. Recovery is dependant on the recovery of prey stocks, for which insufficient information has been found to make an assessment. Hence a moderate sensitivity has been recorded.

Additional information

Recoverability
In general, the recoverability of Dipturus batis after a mortality event from any source is very slow. Skates live for at least twenty years, reach maturity at 11 years and the females produce a clutch of about 40 eggs every other year (see reproduction). This means that a female produces a minimum of about 160 eggs in its lifetime, a very low fecundity. Even if every juvenile born after a mortality event survived, it is evident that it would take many years for a population to recover to its original numbers.

Importance review

Policy/legislation

UK Biodiversity Action Plan Priority
Species of principal importance (England)
Species of principal importance (Wales)
Scottish Biodiversity List
OSPAR Annex V
IUCN Red ListCritically Endangered (CR)
Features of Conservation Importance (England & Wales)
Priority Marine Features (Scotland)

Status

Non-native

Importance information

When it was common, skate used to taken as bycatch in trawls and the 'wings' were sold for human consumption.

Dipturus batis is listed under the UK Biodiversity Action Plan (Anon, 1999vii) and on the OSPAR Annex V list of threatened and declining species and habitats. Although listed as 'endangered' in the IUCN Red list, it is considered to be 'critically endangered' in coastal waters (IUCN, 2003). In addition, Dipturus batis has been proposed for protection under Schedule 5 of the Wildlife & Countryside Act 1981.

Bibliography

  1. Anonymous, 1999vii. Common skate (Raja batis). Species Action Plan. http://www.ukbap.org.uk/asp/UKPlans.asp?UKListID=543, 2004-01-20

  2. Brander, K., 1981. Disappearance of common skate Raja batis from Irish Sea. Nature, 290, 48-49.

  3. Bruce, J.R., Colman, J.S. & Jones, N.S., 1963. Marine fauna of the Isle of Man. Liverpool: Liverpool University Press.

  4. Bryan, G.W., 1984. Pollution due to heavy metals and their compounds. In Marine Ecology: A Comprehensive, Integrated Treatise on Life in the Oceans and Coastal Waters, vol. 5. Ocean Management, part 3, (ed. O. Kinne), pp.1289-1431. New York: John Wiley & Sons.

  5. Dipper, F., 2001. British sea fishes (2nd edn). Teddington: Underwater World Publications Ltd.

  6. Dolgov, A.V., Drevetnyak, K.V. & Gusev, E.V., 2005. The Status of Skate Stocks in the Barents Sea Journal of Northwest Atlantic Fisheries Science, 35, 249-260

  7. Hayward, P.J. & Ryland, J.S. (ed.) 1995b. Handbook of the marine fauna of North-West Europe. Oxford: Oxford University Press.

  8. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  9. Hureau, J.C. & Monod, T., (ed.) 1973. Check-list of the fishes of the north-eastern Atlantic and of the Mediterranean. Paris: Unesco

  10. IUCN, 2006. 2006 IUCN Red List of Threatened Species. [On-line] http://www.redlist.org, 2003-01-01

  11. Jennings, S., Greenstreet, S.P.R. & Reynolds, J.D., 1999. Structural change in an exploited fish community: a consequence of different fishing effects on species with contrasting life histories. Journal of Animal Ecology, 68, 617-627.

  12. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line] http://www.jncc.gov.uk/mermaid

  13. Little, W., 1995. Common skate and tope: first results of Glasgow museum's tagging study. Glasgow Naturalist, 22, 455-466.

  14. Little, W., 1997. Common skate in the Sound of Mull. Glaucus, 8, 42-43.

  15. Little, W., 1998. Tope and skate tagging off west Scotland. Glaucus, 9, 36-38.

  16. McEachran, J.D. & Dunn, K.A., 1988. Phylogenetic analysis of skates, a morphologically conservative clade of elasmobranchs (Chondrichthyes: Rajidae). Copeia, 2, 271-290.

  17. Mitchell, S. & Gallagher, M., 2000. The parasitic copepod Acanthochondrites annulatus (Olsson, 1869) from the blue skate Raja batis. Irish Naturalists' Journal, 26, 323-323.

  18. Muus, B.J. & Dahlstrom, P., 1974. Collins guide to the sea fishes of Britain and North-Western Europe. Wm Collins Sons & Co. Ltd: London.

  19. Rogers, S.I. & Ellis, J.R., 2000. Changes in demersal fish assemblages of British coastal waters during the 20th century. ICES Journal of Marine Science, 57, 866-881.

  20. Sutcliffe, R., 1994. Twenty years of tagging common skate and tope off the west coast of Scotland. In Tag and release schemes and shark and ray management plans. Proceedings of the second European Shark and Ray Workshop, Natural History Museum, London, 15-16 February 1994 (ed. R.C. Earll & S.L. Fowler), pp. 14-16., Peterborough, Joint Nature Conservation Committee

  21. Vella, G., Rushforth, I., Mason, E., Hough, A., England, R., Styles, P, Holt, T & Thorne, P., 2001. Assessment of the effects of noise and vibration from offshore windfarms on marine wildlife. Department of Trade and Industry (DTI) contract report, ETSU W/13/00566/REP. Liverpool: University of Liverpool., Department of Trade and Industry (DTI) contract report, ETSU W/13/00566/REP. Liverpool: University of Liverpool.

  22. Walker, P.A. & Hislop, J.R.G., 1998. Sensitive skates or resilient rays? Spatial and temporal shifts in ray species composition in the central north-western North Sea between 1930 and the present day. ICES Journal of Marine Science, 55, 392-402.

  23. Whitehead, P.J.P., Bauchot, M.-L., Hureau, J.-C., Nielson, J. & Tortonese, E. 1986. Fishes of the North-eastern Atlantic and the Mediterranean. Vol. I, II & III. Paris: United Nations Educational, Scientific and Cultural Organisation (UNESCO).

Citation

This review can be cited as:

Neal, K.J. & Pizzolla, P.F 2006. Dipturus batis Common Skate. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/species/detail/1436

Last Updated: 13/12/2006

Tags: fish skate ray