Migrating wildlife
Wildlife is rarely static, often moving from place to place. Many marine species spend their lives within the sea but spawn within rivers, whilst many species of wading bird travel using the coast. Some examples of this include;
Lampreys
Are some of the phylogenetically oldest fish in the world, with some examples being the oldest fossils found. Most species are coastal and freshwater, requiring 'clean gravel' found within rivers for spawning and silt beds for juvenile larvae to burrow into. Lampreys are present in the Humber throughout the year, when ready to spawn they swim into smaller rivers to spawn. They require good water quality at all stages of their life and are highly sensitive to pollution. They cannot pass through barriers such as dams and weirs when migrating, resulting in often an inability to find spawning grounds.
Lamprey ecology is relatively poorly understand. These jawless fish have a large sucker covered with teeth, used for hanging on to the sides of other fish where they use their rasping tongue to feed on the blood of the other fish, as such they are considered parasitic. They are often found to feed on Salmon.
Lamprey are regularly used as bait by freshwater fishermen, this is discouraged as can significantly threaten their numbers.
Sea lampreys are one of the largest species found in our rivers and can grow up to 2.2kg in length and as thick as a mans arm. Three different species are known to occur within the UK, Sea, River and Brook Lamprey. We are now seeing a number of areas being proposed for protection of lampreys due to their high sensitivity to pollution and construction.
Salmon
Salmon are anadromous, meaning that they spend most of their lives in saltwater, but return to freshwater to breed. Salmon do not need saltwater, though, and there are salmon population which spend their whole life in fresh water (‘landlocked’ salmon)
The amount of time that a juvenile salmon will spend in its natal stream varies from 2-6 years. Average age correlates with temperature exceeding 7⁰C. Salmon can grow up to 1.5m. During the breeding season, they must swim upstream to spawn, often overcoming obstacles such as waterfalls as they do so. They have an amazing ability to be able to leap 12 feet in the air. Salmon always return to the stream that they were born in to spawn, and current theory is that it is due to the particular chemical identity of the water- they find the right stream using their sense of smell.
In the last 30 years, the salmon population has experienced a huge decline, and catches have fallen by 80%. Many populations are on the brink of extinction or have been lost. It is believed that Atlantic Salmon numbers are only reasonably healthy in four countries- Norway, Iceland, Scotland and Ireland. In the UK, populations in almost 505 of rivers are at risk, and 30% are endangered.
Salmon only return to pristine rivers, and so are good indicators of water quality. The decline of the Atlantic Salmon has been connected to industrial development. River pollution can severely damage numbers, and the building of dams and changing of the watercourse can make migration impossible. Salmon farming may also be a factor in their decline, as they can spread diseased throughout wild stock, and escaped individuals may erode the gene pool.
Some conservation measures have been put in place, but populations are not recovering. Research is being undertaken to find out why this might be.
The young salmon spend a few days at the mouths of estuaries, getting used to the saltwater, before heading out to sea.
After spawning, most of the cock fish die. Some of the hen fish, and only one or two cock fish will survive. Very few make it back to the sea where the salt water helps them recover. They do not eat in the freshwater rivers, before or after spawning. Occasionally, fish will live to spawn two or three times.
Scientists have created a GM salmon that grows at twice the rate of a normal salmon. There are very large protests against farming this GM salmon, due to concerns with the genes entering into the environment.
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