BIOTIC Species Information for Dipturus batis
|Researched by||Ken Neal & Paolo Pizzolla||Data supplied by||MarLIN|
|Refereed by||This information is not refereed.|
|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|
|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,|