Allis shad (Alosa alosa)
The allis shad is native to Ireland and occur in very low numbers in coastal waters and estuaries in the Southeast. Their geographic range includes the coastal waters and inflowing rivers of the Atlantic coast of Europe and the Mediterranean Sea. There are no recent records of spawning populations in Ireland; therefore, allis shad caught in Irish waters probably originated from European populations.
Allis shad are very similar in appearance to twaite shad (Alosa fallax), and these two species may interbreed. The two species are difficult to tell apart from physical appearance or colour alone, and in the lab, they are distinguished by examining the anatomy of their gills. Allis shad are deep bodied and herring-like in appearance, with a sharp keel on their belly, radiating lines on the gill covers and a distinct notch in the upper jaw. They are typically a little bigger than twaite shad and often have a large dark blotch on their head just behind their gill covers, without blotches along their sides.
Allis shad feed on invertebrates, plankton and small fish in coastal waters. In European rivers where they spawn, allis shad sometimes travel great distances upstream and will usually only spawn once.
Allis shad appear in low numbers in Ireland, and there is not sufficient data to establish their conservation status in Irish waters. Threats to allis shad include pollution; commercial fishing, which may accidentally capture shad as by-catch; and barriers to migration. Indeed, barriers may be partially responsible for hybridisation with twaite shad by blocking access to upstream spawning grounds.