The adult shad is a saltwater fish that move into rivers to breed. A significant part of the marine diet of allis shad is composed of larger plankton, whilst the twaite shad take mostly smaller fish species such as anchovy. The young shads remain in rivers and estuaries, feeding on invertebrates on the bottom, until they are large enough to survive the open sea. Adults of both species enter rivers to spawn.
Classified as Vulnerable by the British Red Data Book. Protected under Schedule 5 of the Wildlife and Countryside Act, 1981. Listed under Annexes II and V of the EC Habitats Directive and Appendix III of the Bern Convention.
The two shad species have declined as a result of a variety of factors, including the construction of river barriers such as weirs and barrages, pollution of their spawning rivers, overfishing and habitat deterioration. Weirs and barrages prevent adults from reaching their spawning grounds, and standard salmon fish-passes at weirs or locks encourage turbulent water flow patterns, which shad actively avoid. The shad is more sensitive to pollution than other similar estuary species and have been forced out of many rivers where they formally occurred, including the River Thames.
The shads are vulnerable species, allis shad more so than twaite in the UK. Several plans are in place to try and recover their populations. A plan involving the Countryside Council for Wales (CCW), the Environment Agency (EA) and English Nature has been set fish
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