Allis & Twaite Shads
Shad are herring-like fish that spend most of their adult lives in the sea but spawn in rivers (or, occasionally, in the upper reaches of estuaries) and usually migrate through estuaries in spring months on their way to the spawning grounds. Distinguishing between species is done by their size (Allis shad, Alosa alosa, are usually 30-50cm, Twaite shad, Alosa fallax, 25-40cm), the number of scales running along the lateral line, and the number of gill rakers on the first gill arch.
There are few records of shad in the SAC. Both are considered to be nationally rare and vulnerable, the Allis shad more so than the Twaite. Joint national work seeks to identify key rivers and spawning sites for both species.
Both species are vulnerable to fishing (as a bycatch), pollution, and river obstructions to migration (especially as their deep keeled body prevents them from using fish passes). It is an offence to intentionally obstruct access to spawning areas or to damage or destroy gravels used for spawning.