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1 and 2. Allis shad Alosa alosa and Twaite shad Alosa fallax. 3 and 4. River Lamprey Lampetra fluviatilis and Sea lamprey Petromyzon marinus.
Allis shad Alosa alosa and Twaite shad Alosa fallax. The shads are anadromous (spending part of their life cycle in the sea but migrating to fresh water to breed) members of the herring family. Shad have streamlined, laterally flattenened bodies with a deep keel. The body (but not the head) is covered by large silvery scales which gives them a metallic sheen. The two species mentioned look very similar, and are extremely difficult to distinguish by sight (the easiest identification method involves counting the number of gill rakers on the first gill arch).
Allis shad Alosa alosa , the larger of the two species, measure 30-50cm and grow in coastal waters and estuaries before migrating into rivers to spawn (up to 100km upstream). It is rare throughout it's range (the western coasts of Europe, from southern Norway to Spain and in the Mediterranean eastwards to northern Italy) and is not known to breed in the UK but can be found in the Loughor and Tywi rivers within the Carmarthen Bay cSAC. The twaite shad Alosa fallax, measuring 25-40 cm, can be found along the western coastline of Europe from southern Norway to Morrocco and along the eastern Mediterranean. It spawns in lower reaches of rivers than the allis. It is reported to breed in seven UK rivers including the Tywi. Both species are vulnerable to overfishing (as a bycatch), pollution and river obstructions to migration (especially as their deep keeled body prevents them from using fish passes). The allis shad is particularly vulnerable to migration obstruction as it spawns further upriver than the twaite. It is thought that one reason for the species' decline is that it has interbred with twaite shad where there are obstacles preventing it getting upriver to it's normal spawning grounds. The resultant offspring have then bred with the twaite as the habitat in the lower river favours them. Over time this has resulted in the offspring becoming more like the twaite and less like the allis.
River Lamprey Lampetra fluviatilis and Sea lamprey Petromyzon marinus. Lampreys are jawless fish which have a simple skeleton of cartilage. Unlike many more familiar fish they do not have paired fins or scales. Although they have an eel-like body shape they can be distinguished from eels by their sucker-like mouth disc and seven pairs of gill slits. These two species are parasitic on other fish. They scrape a hole through the prey's skin, cling on with their mouth disc, and draw out blood.
River lampreys Lampetra fluviatilis are anadromous. After five years in fresh water the river lamprey spends one or two years in the sea (probably staying near the shore) before migrating back up river, perhaps hitching a ride (and getting a meal at the same time) from another fish. It does not feed once it has reached fresh water and spawns in the upper reaches of the river the next spring. This species has been selected as a feature for the Carmarthen Bay and Estuaries cSAC as the site has a healthy population which has clear water and subtrates for spawning. Sea Lampreys Petromyzon marinus are larger than river lampreys but have a similar life cycle. They do, however, venture further out sea and spawn in lower reaches of the rivers than the river lampreys. Pollution and obstacles to migration (such as dams or weirs) can cause decline in numbers of both species.
Otters Lutra lutra historically existed over most of the UK. They can be found on estuaries and open shores, but they do rely on being close to fresh water for the majority of their food, to wash salt water from their fur and to provide suitable habitat for resting and building holts. They have a varied diet including salmonid fish, crayfish, eels, toads and young birds.
Persecution, habitat loss and drainage and pollution of waterways led to a drastic decline of otter numbers during the 1950s and 60s. At present the UK otter population, important for its genetic diversity, has made a marked increase since the mid 1980s due to water pollution controls and favourable land management methods. The Carmarthen Bay cSAC contains extensive tracts of prime otter territory and they can be found within the 4 rivers and along our open coastline. The River Towy has always been a strong hold during periods of decline elsewhere whilst the Loughor has been recolonised within the last five years. |
