Rays as a group are often fairly difficult for the average angler to identify, but the cuckoo ray is the exception to this rule. Along with the undulate ray, it is one of the two British species that are so clearly marked that its identification is both certain and immediate.
Spot the spots
The cuckoo ray belongs to the small group of ‘round-winged’ rays in which the edges of the wings are smoothly curved. Its short snout is also rounded, with a small upturned tip.
Except for a smooth patch on each wing, the skin on the back is covered with prickles, making it feel rough. The underside of the snout is also rough to the touch.
There are four rows of curved, closely packed spines running along the tail, but not down its midline. The two central fines also extend up the back but become irregular. The back is a blotchy light brown in colour, the underside white or grey.
In the middle of the wings are two conspicuous black and yellow round marks. It is these spots that give this ray its scientific name Raja naevus – naevus is Latin for a birthmark. Why it is a ‘cuckoo’ ray is inexplicable; it certainly does not make a noise like the bird.
Deep water dwellers
Like most rays, this is a bottom-living fish. It is most abundant in deep water between 70-100m (230-330ft), but can be found in water as shallow as 20m (66ft). Because it lives in fairly deep water it is not often caught by anglers, but it is taken in large numbers by commercial fishermen.
As with many rays, details of its biology are unknown. For example, no studies have been made of its diet. Our knowledge is therefore based on isolated notes made on just a few specimens. When young it eats mainly small crustaceans and worms. Larger cuckoo rays eat fish of various kinds, particularly those that five near the sea bed such as sandeels, gobies and dragonets.
They are also reported to eat large numbers of herrings and sprats. If this is so, it means they are feeding well off the bottom. Certainly the rather long pointed teeth of the cuckoo ray suggest that it is adapted to catching and eating fast-moving prey like these mid-water shoal fish.
The cuckoo, like all rays, lays its eggs in tough horny cases, called ‘mermaid’s purses’. They are light brown (though they can be almost transparent) and rather small – about 6cm by 4cm (2%in by Vain) excluding the horns at each corner. The forward pair of horns are longer than the rear pair which have in-curving tips. Newly hatched rays are only 12cm (43/4in) long. Each mature female produces some 90-100 eggs which she lays throughout the year. In aquarium conditions the eggs hatch in about 240 days, though in the sea, where the temperature is generally lower, they may take longer.