Seven of the Severn
The fish fauna of the Severn Estuary is very diverse . More than 110 species of fish have been identified, which include seven different species of migratory fish, more than any other British estuary! The estuary is one of the most important British estuaries for several rare species, including river lamprey, sea lamprey and twaite shad.
The estuary serves as a nursery area for juvenile fish where they feed heavily on small items of plankton. The Severn Estuary supports a run of migratory salmon. These fish pass through the estuary on their way to and from their spawning grounds in the upper reaches of the rivers and the open sea. The Estuary also has the largest eel run in the country.
European Eel (Anguilla Anguilla)
European Eels begin their life as eel larvae, drifting from their birthplace in the Sargasso Sea for three years across the Atlantic Ocean on ocean currents to the Severn Estuary. Here they metamorphose into cylindrical, unpigmented 'glass eels' and then becoming more pigmented 'elvers'. This freshwater phase is a feeding and growing stage, before they migrate out of the estuary to the open sea. They feed on invertebrates and small fish in the estuary.
The elver fishery on the Severn lasts from January until the end of May and during that time thousands are caught and sold to elver stations, form where they are exported live to Europe and Japan for restocking. There are established elver fisheries on the rivers Parrett, Severn, Wye and Usk. Silver eels (seaward travelling) are caught commercially in the River Severn in the Gloucester area. Yellow eels (estuary bound) are caught in the River Severn and other tributary rivers using fyke nets and putcheons. There is concern about the elver fishery declining.
River and Sea Lamprey
The river and sea lamprey are a primitive type of fish having a distinctive suckered mouth but no jaws. Although numbers of lamprey have declined over the last 100 years, the UK is still one of their strongholds. Sea and river lampreys spend their adult life in the sea or estuaries but spawn and spend the juvenile phase in rivers. They use the Severn Estuary as a migratory passage to and from their spawning and nursery grounds in the rivers.
Salmon migrate through the estuary and its associated rivers such as the Severn, Wye, and Usk. Rarely feeding on its journey, and by the time they arrive at the spawning ground, the females are plump with eggs, and the males have developed distinctly hooked jaws. The females use their tails to excavate hollows in the gravel of the stream-bed, and the males lie alongside and fertilise the eggs as they are laid. Adult Atlantic salmon may die after spawning, but unlike other salmon a large number of the adults often survive, making their way back to the open sea emaciated and exhausted.
Some of the net fishing methods used on the Severn Estuary are unique to the area and have a long history. Notably Lave netting (using a 'Y' shaped net and 'stalking' or 'cowering' in the shallows to catch the salmon migrating), and putcher nets (rows of baskets which use the ebb tide to trap salmon).
To find out more on the traditional types of fishing visit www.salmonboats.co.uk/
Allis Shad (Alosa alosa) and Twaite Shad (Alosa fallax)
Allis and twaite shad are the only two members of the herring family found in fresh water in the UK. Both look like large herring (adult allis shad can be over 2 kg in weight), and were formerly eaten in this country before numbers declined and the fisheries collapsed. In the middle of the 19th Century, the value of shad rivalled that of salmon, and in the River Severn, shad made up about one-third of all catches. The fish enter estuaries in early spring and move up into the rivers. Nocturnal spawning over gravel beds occurs in April / May, before they return to the sea by the end of summer.
Sea Trout (Salmo trutta)
The habits of this species are also very like those of the Salmon, and the females are said to run up the rivers before the males.
Trout breed in winter, from October to January, sometimes to February, usually in temperatures of 5-10°C (41-50°F). Sexual maturity occurs in males at two years, in females at three years of age. Spawning always occurs on gravelly shallows, in which the female cuts a redd by means of flexions of the tail. The eggs are shed and are fertilised immediately by the male, which stations himself beside but slightly behind the female. The eggs are buried by the female in later redd digging, and hatch in about forty days at a temperature of 10°C (50°F). The fry (alevins) hatch at a length of ½-1 in (15-25 mm), and the yolk sac is absorbed in four to six weeks, after which they commence feeding. A general downstream migration follows hatching.