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?	No
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 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	No
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
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