Research on Scottish skate led to an exciting discovery with implications for conservation. Karen Boswarva reports
OCEANSCIENCE
One becomes two!
Research on Scottish skate led to an exciting discovery with implications for conservation. Karen Boswarva reports
Ask a diver in Scotland what UK marine animal is on their bucket list, and they’ ll probably tell you the flapper skate( or common skate). An enigmatic fish of impressive proportions, it reaches six feet wide and 8 feet long from rostrum( nose) to tail tip! It is a true ocean giant and the world’ s largest marine skate. It lives and breeds in the seas surrounding the west and north coasts of Scotland, its last stronghold following extinctions across much of its historical range.
The common skate( Dipturus batis) was classified as Critically Endangered on the IUCN Red List; as a species they face an extremely high risk of extinction in the wild. They are identified as a Scottish Priority Marine Feature and a European Priority Species and are afforded protection by law. Since 2009 it has been illegal for fishermen to retain and sell common skate caught as bycatch. They must be returned as quickly as possible to maximise chances of survival.
On the west coast of Scotland, the first UK elasmobranch Marine Protected Area( MPA) and largest MPA for a mobile species was designated in 2016 to protect a residential population of common skate. Designation of the site was led by a local group of sea anglers who continue to work with researchers and statutory bodies to provide effective management of the MPA.
Sea angling for common skate is strictly catch-and-release; the anglers collect vital data before returning the skate as quickly and safely as possible. Masses of information can be obtained from each common skate: size, weight, sex, maturity. Every common skate has a unique pattern of spots and scars – a fingerprint for tracking an individual’ s movements. A clear picture of the dorsal( top) side can be submitted to a database called Skatespotter( check it out … it’ s a fantastic resource).
Researchers have tagged common skate with tiny transmitters to understand the range and depth of habitats they use. The results are fascinating – males and females of different age classes will use different habitats and depths throughout the year. Some remain local all year round, while others depart and return periodically. One even made the journey across and back from the Celtic Sea! A true ocean explorer.
Baited cameras are a newer method of monitoring common skate, a technique that minimises disturbance. Video cameras are attached to a metal frame that contains a small amount of bait( to attract the skate). These frames are left on the seabed and recovered after a set time period. An analyst will review the footage and record any common skate that pass by the frame. The position and placement of cameras can be used to ID, measure, and sex common skate while providing wider habitat and species information.
If you’ re a species nerd( raises hand) you’ ll be more than aware of those pesky geneticists changing the name of species our brains have only just begun to remember.
Well, the common skate is no exception. Genetic testing of DNA led to some significant findings. The common skate was, in fact, not one but two species!
And so, the common skate Dipturus batis became what we call the common skate complex, comprising the flapper skate( Dipturus intermedius) and the blue skate( Dipturus batis).
This represents a conservation conundrum. Both species are afforded the same protections. Yet since the split, the blue skate remains largely in the shadows of its largerthan-life cousin. West coast populations appear to represent the flapper skate populations only, meaning little is known of the blue’ s true range and abundance. Clues reside in Orkney waters, where baited cameras show both species utilising the same habitat, visiting the camera moments apart. It is this footage that has helped scientists determine one species from the other.
Mature male blue skate are the size of juvenile male flapper skate; the rostrum of a blue skate is thinner and pointier, and the dorsal spots more uniform. Occasionally, an egg case will wash ashore among flapper skate eggs, clear from the size that they are different species.
Evidence like this will gradually improve knowledge of preferred blue skate habitat, eventually untangling the complex, to ensure blue skate gain targeted conservation measures, and the leaderboard on our bucket lists. �
Above flapper skate above, blue skate below
PHOTO: DAN WISE ORKNEY SKATE TRUST
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