Essex Biodiversity Project
Allis and Twaite Shad
Identification - Shads are members of the herring family. They have distinctive large round scales that form a toothed edge on the underside. They have large eyes with fleshy eyelids with membranes covering the front and rear parts of the eye. It has small fins and the tail has pointed areas of scales almost reaching a fork.
They are silvery fish with a green - blue sheen on the back and a golden sheen on the head. The Twaite shad has six to ten spots along it side, whereas the Allis shad has only three. The Twaite shad is 25 - 40 cm and the Allis Shad is larger being 30 - 50cm.
General ecology - Both shad species reproduce in fresh water and grow in the sea. Little is known about their preferred habitats at sea but they can swim up to 150km up streams and rivers. Twaite shad occur offshore on the Essex coast and are sometimes caught around the Blackwater and Thames estuaries. Although there is no evidence of spawning (egg laying) in these rivers, barriers may now prevent migration. Water quality and river management (flood barrages) are thought to be the main reason for decline. Accidental catches of the species by coastal fishing is not considered significant to its decline.
Surveying tips - Reports of catches by fishermen/women contribute to the recording of the species. Let us know if you think you have caught a Shad - a photograph would be excellent.