The allis shad, Alosa alosa (Linnaeus), and the twaite shad, Alosa fallax (Lacepede), are both members of the herring family, Clupeidae. The shads form a large group of pelagic fishes found in seas all over the world except the Antarctic. Most are marine, but some enter fresh water to spawn, their young subsequently coming back to the sea to grow, and a few live permanently in fresh waters.

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 (adults can be over two kg in weight) and were formerly eaten in Britain 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 estuary of the River Severn, shad made up about one-third of all catches. Both allis and twaite shad have declined across Europe and they are now absent from many rivers where they once flourished and supported thriving fisheries. They are still caught and eaten in parts of France and some other European countries.

The allis shad is found along the coasts of western Europe from southern Iceland and Norway to Spain, and in the Mediterranean eastwards to northern Italy. It is native to 12 of the present 15 countries of the European Union. It occurs mainly in shallow coastal waters and estuaries, but during the spawning migration it penetrates well upstream in some of the larger European rivers. A few landlocked populations have been recorded, at least some of these being of recent origin, due to the stocks being trapped in reservoirs above impassable dams.

The allis shad has suffered considerably from pollution, over-fishing and river obstructions, and is now a rare fish over most of its range. Although previously believed to spawn in some British rivers, such as the River Severn, they have been caught only rarely in recent years. There are now no known spawning sites for this species in Britain.

Because of this decline, the allis shad is now given considerable legal protection. It is listed in annexes IIa and Va of the Habitats Directive, Appendix III of the Bern Convention, Schedule V of the UK Wildlife and Countryside Act (1981) and as a Priority Species in the UK Biodiversity Action Plan.

The twaite shad, Alosa fallax, occurs along most of the west coast of Europe, from southern Norway to the eastern Mediterranean Sea, and in the lower reaches of large accessible rivers along these coasts. There are several non-migratory populations of this fish in a few of the larger European lakes, including Como, Garda, Iseo, Lugano, Maggiore and Lough Leane.

With the exception of these isolated populations, the normal habitat of this species is the sea and the lower reaches of large unpolluted rivers where there is easy access to spawning grounds. In general, populations of twaite shad have declined across Europe, though not as severely as the allis shad.

In the UK, spawning populations of twaite shad are still found in the rivers Severn, Wye, Usk and Tywi and appear to be reasonably stable. Remnant populations may still be present in other rivers, especially where spawning takes place in estuaries. In Ireland, though there has been a decline, spawning populations still occur in the Rivers Suir, Nore and Barrow, and the Cork Blackwater.

Because of this decline, the twaite shad is now given legal protection. It is listed in annexes II and V of the Habitats Directive, Appendix III of the Bern Convention, and as a Priority Species in the UK Biodiversity Action Plan.

Ecology of the Allis and Twaite Shad

Monitoring the Allis and Twaite Shad