Armour-plated sturgeon

Armour-plated sturgeon

The sturgeon is essentially a sea fish though since it swims up rivers to spawn it is counted as the biggest fish ever to be found in fresh water in Britain. One of the largest freshwater specimens recorded was caught in 1933 in the Towy near Carmarthen; weighing 388 lb (176kg), it was 2.8m (9ft 2in) long and was caught by an angler fishing for salmon. It was foul-hooked and after being played for a while, eventually stranded itself in the shallows where it was beaten to death with a rock! (as a result it never made British record status; in fact there are no British rod-caught sturgeon records at all.)

The unusual nature of the event lies both in the size of the fish in a fairly small river and that an angler caught it. Sturgeon are not thought of as an angling species — they are difficult to catch on rod and line since, like salmon, they come into rivers to spawn, and feed very little in fresh water. British rivers these days are mostly impassable for such large fish.

Identification is certain in British waters: no other fish has the five series of big bony plates on its back and sides – one row on the mid-line of the back, a pair running along the sides and another pair on the lower flanks. The tail is shark-like, with the backbone turning upwards into the upper lobe of the fin. The bony sculptured head is another recognition feature. The sturgeon is greenish grey on top and paler underneath, with pinkish fins.

Feeding habits

Surprisingly for such a huge and economically important fish, very little is known about its diet. Young fish are believed to feed on bottom-living insect larvae, worms, crustaceans and molluscs in the river. Adults feed on the same type of creatures in the sea, but also take sandeels, gobies and small flatfish.

The sturgeon’s mouth, very small for a fish of its size, is sited on the underside of the head and can be protruded to form a thick-lipped tube. The four barbels on the underside of the snout, just in front of the mouth, are highly sensitive and successful in locating food. The fish uses its long snout to dig food items out of the sea or river bottom, then sucks them up with the tubular mouth.

Vulnerable life-style

A very rare fish today, the sturgeon is scarce along the whole Atlantic coastline including the Baltic and into the Mediterranean. In the Black Sea, including the mouth of the River Danube, it is caught fairly frequently. The only other river system in which it occurs regularly is the Gironde-Garonne opening into the Bay of Biscay. Here French fishery workers have a successful programme of hatching sturgeon eggs and restocking the rivers. It’s these fish that wander into British waters. They are even more vulnerable since they spawn in fresh water and migrate to the sea, in the process facing such hazards as pollution, dams and industrial development.

Adults enter the rivers in February and March and migrate upstream, from May to August spawning in deep pools of swiftly flowing water over gravel beds. After spawning they return at once to the sea.

The dark grey or brown eggs stick to gravel and rocks in the river bed, hatching in three to seven days, depending on temperature. The young move downstream in their first year, growing up to 20cm (8in) long, but don’t go out to sea until two or three years old and 45cm (18in) long.