BIOTIC

BIOTIC Species Information for Dipturus batis

Researched by

Ken Neal & Paolo Pizzolla

Data supplied by

MarLIN

Refereed by

This information is not refereed.

Taxonomy

Scientific name

Dipturus batis

Common name

Common Skate

MCS Code

ZF86

Recent Synonyms

Raja batis

Phylum

Chordata

Subphylum

Pisces

Superclass

Gnathostomata

Class

Chondrichthyes

Subclass

Elasmobranchii

Order

Rajiformes

Suborder

Family

Rajidae

Genus

Dipturus

Species

batis

Subspecies

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).

Taxonomy References

Hayward & Ryland, 1995b, Muus & Dahlstrom, 1974, McEachran et al., 1998, Howson & Picton, 1997, Dipper, 2001,

General Biology

Growth form

Pisciform

Feeding method

Predator

Mobility/Movement

Swimmer

Environmental position

Demersal

Typical food types

Bristle worms, sand eels, crabs and flatfish

Habit

Free living

Bioturbator

Flexibility

Low (10-45 degrees)

Fragility

Intermediate

Size

Large(>50cm)

Height

Growth Rate

0.9 - 14 kg/year

Adult dispersal potential

100-1000m

Dependency

Independent

Sociability

Solitary

Toxic/Poisonous?

General Biology Additional 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).

Biology References

Muus & Dahlstrom, 1974, Sutcliffe, 1994, Walker & Hislop, 1998, Brander, 1981, Little, 1998, Little, 1995, Mitchell & Gallagher, 2000, Anon, 1999vii,

Distribution and Habitat

Distribution in Britain & 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 part of the Baltic and western and northern Mediterranean.

Biogeographic range

Not researched

Depth range

10 to 600 m

Migratory

Non-migratory / Resident

Distribution Additional 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.).

Substratum preferences

Muddy gravel
Coarse clean sand
Fine clean sand
Sandy mud
Muddy sand
Mud
Mixed

Physiographic preferences

Open coast
Offshore seabed

Biological zone

Upper Infralittoral
Lower Infralittoral
Upper Circalittoral
Lower Circalittoral

Wave exposure

Very Exposed
Exposed
Moderately Exposed
Sheltered
Very Sheltered

Tidal stream strength/Water flow

Strong (3-6 kn)
Moderately Strong (1-3 kn)
Weak (<1 kn)
Very Weak (negligible)

Salinity

Full (30-40 psu)

Habitat Preferences Additional Information

Distribution References

Hayward & Ryland, 1995b, Muus & Dahlstrom, 1974, Dipper, 2001, Walker & Hislop, 1998, Brander, 1981, JNCC, 1999, Rogers & Ellis, 2000, Whitehead et al., 1986, Jennings et al. 1999,

Reproduction/Life History

Reproductive type

Gonochoristic

Developmental mechanism

Oviparous

Reproductive Season

Insufficient information

Reproductive Location

See additional information

Reproductive frequency

Biannual episodic

Regeneration potential

Life span

51-100 years

Age at reproductive maturity

11-20 years

Generation time

11-20 years

Fecundity

Up to 40 eggs

Egg/propagule size

15-25 cm long, 8-15 cm wide

Fertilization type

Insufficient information

Larvae/Juveniles
Larval/Juvenile dispersal potential	Insufficient information	Larval settlement period	Not relevant
Duration of larval stage	Not relevant

Reproduction Preferences Additional Information

Females breed every other year (Little, 1997) and produce up to 40 eggs (Walker & Hislop, 1998) which are laid in sandy gravel 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.

Reproduction References

Muus & Dahlstrom, 1974, Dipper, 2001, Sutcliffe, 1994, Walker & Hislop, 1998, Brander, 1981, Little, 1998, Little, 1995, Hureau & Monod (1973), Rogers & Ellis, 2000, Little, 1997, Whitehead et al., 1986, Bruce et al., 1963,