Although dogfishes lack the glamour of the fast-moving, hard-fighting big sharks such as the tope, blue and porbeagle, they are important to the British sea angler simply because they are so common. (Curiously, where we call them dogfishes the North Americans know them as cat-sharks!)
They have several features common to all sharks – blunt heads and long, tapering bodies with a skeleton made entirely of cartilage (not bone) to give the body greater flexibility. Although sharks lack a swim bladder, their large, oil-filled liver does a similar job, keeping the fish buoyant in the water. The skin of both species is covered with hundreds of fine, backward-pointing ‘teeth’. (In days gone by it was used for polishing wood and copper under the name of’rubskin’.)
Spot the difference
There is often confusion when trying to tell these two dogfishes apart, since the terms greater and lesser refer to the size of the fish, not to the size of the spots. As a result, the names sandy dog (lesser) and nurse hound (greater) are often used.
Both have sandy or grey/brown backs with dark brown spots, and although the nurse hound commonly does have larger spots, these are not an ideal means of identification.
The conclusive way of telling them apart is to look at their nasal flaps. In the sandy dog the nasal flap, which overlaps the upper lip, runs continuously from one nostril to the other. In the nurse hound the two nasal flaps are separate and each is fused with the snout near the midline.
The sandy dog lives in sand or fine gravel, its colouring matching that of the dappled sea bed; it is usually found at a depth of 20-75m (65-245ft). The nurse hound is also a bottom-living shark but is normally found on rockier ground at depths of 20-65m (65-215ft). Both fish stray into much shallower waters at times.
The nurse hound tends to be a bit of a loner, so is not usually caught in large numbers, but the sandy dog frequently forms large schools, often being a nuisance to the bottom-fishing angler. Unfortunately, trawlers fishing over inshore grounds often catch thousands of sandy dogs in a haul, and although they are usually dumped overboard, many are killed in the process.
Most members of the shark family bear their young live, the fertilized eggs staying in the female’s body until maturity – but dogfish differ by laying eggs in cases.
Mating takes place in the autumn, after which the female moves into shallow waters for spawning between November and July.
The cases, also known as ‘mermaid’s purses’, are tough and leathery with tendrils at each corner; these anchor the egg case in place by twining around the stems of seaweed, or round wrecks and other solid structures. The pup remains inside the case for up to a year, feeding off its yolk sac before being ready to hatch.
As youngsters the dogfishes feed on sand hoppers and other small crustaceans before graduating to crabs, shrimps, molluscs and bottom-living fish. The nurse hound also eats large crabs (especially hermits), octopuses and even smaller dogfish.