Return Of The King

Return Of The King Salmon’s Reappearance in the River Don Don Catchment Rivers Trust

Few species evoke images of pristine rivers more than the salmon. The ‘king of fish’, as it’s sometimes called, is a staple of the nature documentary, usually scaling waterfalls and narrowly avoiding the jaws of a grizzly in the wilds of North America. It therefore often surprises people in South Yorkshire when they learn that the River Don once sustained a huge salmon population. It is precisely this iconic status of the species and its connotations of healthy rivers that has been one of the motivating factors behind efforts in recent decades to help salmon recolonise the Don. If salmon returned, so the reasoning goes, then people would take note, recognising that the Don is valuable habitat for wildlife and no longer the foully polluted and smelly river it once was. Perhaps, after years of neglect, people would begin to treat the river better, questioning whether to throw in that empty drinks bottle or reconsidering what they pour down the drain. If people felt more positive about the river then it would be given a greater voice in decision making, such as investing more resources in improving it. The species of salmon native to Britain is known as Atlantic Salmon (Salmo salar). It is actually more closely related to the Brown Trout (Salmo trutta), another native fish, than the world’s six other salmon species, which all inhabit rivers draining into the Pacific. Young salmon live in freshwater, before migrating out to sea and travelling to their feeding grounds in the North Atlantic. After one or more years at sea they return to their river of their birth to spawn and reproduce in swift flowing and relatively shallow river habitat (see page 21 for Life Cycle & Salmon Terms). Records show that salmon were once plentiful in the Don. Hecks (a type of salmon trap) were used to catch migrating fish in 17th century Doncaster, and next to nothing prices from market records show traders might have considered salmon to be inexhaustible. Two factors led to its loss from the Don. The first was the construction of large numbers of ever bigger weirs, built largely to draw water from the river to power water mills, or maintain water levels so boats could navigate the river and canal. These dam-like structures form barriers for the migrating salmon, and made it increasingly difficult for them to reach spawning habitat in the upper parts of the catchment. The second factor was the gross pollution of the Don caused by the growth of industry and mining and a burgeoning population. So extreme was this pollution that by the 20th century, much of the Don stank, it regularly turned yellow and was dead to plants and wildlife. In recent decades a remarkable recovery of the River Don has got underway, largely due to improvements in water quality resulting from the decline of heavy industry, better regulations, and improved treatment of sewage. While many water quality issues still remain, the fact that salmon’s relatives, trout and grayling, are now doing well in the Don shows that the water is clean enough for salmon too. So how do you get salmon back to the Don? Well salmon have been attempting to migrate up the Don for a number of years, and have been observed jumping in vain to ascend barriers on the lower half of the river. You may be wondering why salmon are swimming up the Don when their homing instinct should lead them back to where they were born. The explanation is that their “internal satnavs” can make mistakes, and some individuals end up straying into different rivers. For example, one salmon found dead in 1976 downstream of Thorne had been tagged two years earlier on the River Ure in North Yorkshire. This unfortunate individual had taken a wrong turn into the heavily polluted Don on its way up the River Ouse. While the best thing we can do to help salmon return is to remove barriers, many on the Don can’t be as they still have important functions or heritage value. Therefore, over the last two decades various organisations including ourselves, Environment Agency (EA), Yorkshire Water (YW), Canal and River Trust (CRT), and

The current status of barriers on the River Don with regard to how passable they are to adult salmon migrating upstream. the councils of Doncaster, Sheffield and Rotherham have worked to create a migration ‘superhighway’ by installing fish passes (see Fish passes) on barriers. One of the first, built 20 years ago, was a rock ramp and bypass channel to allow fish to circumvent Crimpsall Sluice just upstream of Doncaster. A major step forward was made in 2016 when our Living Heritage of the River Don project (funded by the Heritage Fund, EA and YW amongst others) installed fish passes on five weirs in Sheffield. Currently all but two weirs downstream of Sheffield need fish passes (see map). The two unaddressed weirs are Sandersons Weir in Sheffield, on which the council has nearly finished constructing a pass, and Masbrough Weir in Rotherham. At the time of writing we are about to start building a pass on this last structure. Once these passes are completed, salmon will be able to reach Sheffield much more easily, the first location on the Don after leaving the sea where there is suitable habitat for the salmon to reproduce (though larger amounts of better habitat occurs upstream of Sheffield). has been a range-wide decline in the abundance of Atlantic Salmon. The causes are not well understood, though it is thought that climate change is disrupting the oceanic feeding grounds, and the fish farms are putting a heavy burden on wild salmon through the parasites and diseases they release into the sea. For this reason, the best choice environmentally is not to buy wild or farmed salmon. The return of the king to historic breeding grounds on the Don is something to celebrate, but we must all support the protection of life in our oceans. Ourselves and other organisations continue to improve river habitat and remove barriers to migration to help give the species the best possible chance and maybe one day even flourish again in the Don. Fish passes There are three types of fish pass on the Don; easements, Larinier and a rock ramp. An easement on the River Don can be seen on the Kelham Weir in Sheffield. These fish passes don’t convey much water so are only suitable on smaller weirs. They are often used when a weir has historical value as easements represent only a minor modification to a weir. Sprotbrough falls has an example of a Larinier fish pass. A small section of the weir is removed and replaced with a concrete ramp that is less steep. Metal baffles inside the pass slow the flow of water. At Crimpsal Sluice, just upstream from the centre of Doncaster, is a rock ramp. This was constructed in 2000 by the Environment Agency. At the time it was the only fish pass of its kind in the UK. This pass works by creating a section of rapids in a channel that bypasses the structure.

Excitingly, early indications suggest that the Don’s almost complete migration superhighway is already beginning to work, with two salmon being found in Sheffield in January 2019, the first records of salmon in Sheffield for over 200 years. What’s more, examination of one of these fish showed that it had spawned. In January 2020 another salmon was caught in the River Rother.

A Larinier fish pass on Sprotbrough Weir (Falls)

Salmon life cycle and terms Eggs: Female salmon create protective nests of gravel called redds, into which they lay eggs. Cool, oxygen rich water is needed to keep the eggs healthy, which hatch after 100 days.

Alevin: The newly hatched fish, or alevin, are less than 2 cm long. Rather than find their own food they rely on a nourishing yolk sac until they are ready to leave the redd. Fry: As they are vulnerable to predators fry leave the safety of the redd at night. Dispersing downstream, each fry finds a suitable territory which they will defend from other fish. Parr: As they grow fry develop stripes, becoming what are known as parr. Some remain parr for several years, growing slowly in the river until they are ready to migrate to sea.

Returning Adults: Salmon return to freshwater at any time of the year and may wait in freshwater pools for over a year before spawning in late autumn. They don’t actively feed during this time, surviving off reserves of fat built up at sea, but sometimes instinct means they will go for a well presented angler’s lure! Some salmon become "river mature" and return to spawn after only one year at sea; these, known as grilse, are distinguishable from the older fish by having a more forked tail, a slenderer body, thinner scales, and more numerous spots that are blue rather than black. Females (or ‘hens’) migrate to the spawning sites first where they begin to make their redds, lifting and flicking gravel with their tails into position. Their pheromones attract males (or ‘cocks’) and soon the adult salmon pair up. The males have become colourful, developing a red belly and a distinctive hooked lower jaw, called a kype, to attract females from other males. Female pheromones attract males to their redds and work to synchronise mating, the female releases her eggs and the males fertilise them. Kelts (or Slinks): The majority of salmon die after spawning, having exhausted their fat reserves. However, a small proportion, mostly females, survive and return downstream as kelts (or slinks) to feed and recover in coastal waters, building up fat reserves for another migration. Surveys have shown some kelts have successfully spawned three times!

Smolt: This life-stage prepares salmon for life in the ocean, with smolt undergoing changes to their physiology, body shape and colour. By becoming silvery they are better camouflaged in the sea. They find safety in numbers, banding together and travelling downstream in shoals. Post-smolts: From the North Sea the post-smolts make their way to the North Atlantic to rich feeding grounds. They remain in the sea for one or more years before returning to their home river to reproduce.