How soon after buying my rod licence can I fish?

If you have bought a full licence for this season from the Post Office, by phone or on line on the Post Office website, you are covered to go fishing immediately. You will receive a till receipt (from Post Office branches) or confirmation email from the Post Office (for online or telephone purchases) to confirm that your purchase has been successfully processed.

If you have bought a one or eight day licence you can fish from the start date and start time stated on the licence application. Again, you will receive a till receipt or confirmation email from the Post Office to confirm that your purchase has been successfully processed.

Please note, some websites offer to process your rod licence application for you. There may be a delay between you applying to these websites and us receiving and completing the transaction. You must wait till you receive an email from the Post Office, confirming that the transaction is complete or until you have received your licence before you go fishing

Do I need a licence if I take my young child fishing?

Children younger than 12 do not need to buy a rod licence.  Children aged 12 – 16 inclusive need to purchase a junior licence at £5.00.  If you take a child fishing, we advise that you purchase a licence.  If you are holding or helping to hold the rod you will need a licence.

Remember, many angling clubs and fisheries run introductory angling events to introduce youngsters and adults alike to fishing. Many of these events will have a general or temporary licence, allowing anyone attending to fish without buying their own licence.

For more information, visit our angling events page

Which rod licence should I buy?

Find out what types of licence are available, and which one is right for you.

Find out what types of licence are available, and which one is right for you.

Licence types

There are two categories of licence –

  • Salmon and Sea Trout licences allow you to fish for salmon, sea trout, non-migratory trout, char, coarse fish, eel and smelt;
  • Trout, Coarse Fish and Eel licences allow you to fish for non-migratory trout, char, coarse fish, eel and smelt. You may not fish for salmon or sea trout, but if you subsequently decide you would like to, you can upgrade your licence.

Annual or short term licences are available for each category –

  • Annual licences run from 1 April to 31 March;
  • Eight-day licences are available for any period of 192 consecutive hours, for example 18:00 on a Friday to 18:00 on the following Saturday;
  • One-day licences are available for any period of 24 consecutive hours, for example 12:00 on a Saturday to 12:00 the following day.

Concessionary licences are available for each category. You are entitled to a concession if:

  • You are aged 12 to 16 inclusive (youngsters who have not reached their twelve birthday do not need a licence);
  • You are aged 65 years or over;
  • You have a Blue Badge parking concession or are in receipt of Disability Living Allowance (any rate).
  • Please note, concessionary licences are only available for annual licences.

How do you tell the difference between Salmon and Sea Trout?

  Salmon Sea Trout
General appearance Slender and streamlined More round and thickset
Head Pointed More Round
Position of the Eye Maxilla (bony plate usually alongside mouth) does not extend beyond rear rear of eye Maxilla extends beyond eye
Colour Relatively few spots Often heavily spotted
Scale count (number from adipose fin to lateral line) 10-13 13-16
Fork of tail Usually forked Usually square or convex
Wrist of tail Slender Broader
Handling Easy to pick up by tail Tail slips through hand


How is the age of a sea trout determined?

Age determination of sea trout is usually carried out by scale-reading.  This can be trickier than scale reading for salmon, mainly because of the extensive variation that can occur in feeding activity. Temporary visits to fresh water may be interpreted wrongly as winters until the scale reader gains a wider picture of stock movements and associated local growth patterns.  Where possible, scale reading should be validated by tagging and recapture studies.  Spawning is inferred from single or repeated patterns of loss of the scale edges, followed by further growth rings. [ Scale erosion is part of the recovery process of the body from depleted physiological reserves.]

Do all Atlantic salmon migrate to sea?

No. Although most Atlantic salmon spend part of their lives at sea there are some which are non-migratory. In several lakes in eastern North America there is a form known as a land-locked salmon, Salmo salar sebago (Girard), though their access to sea is not barred. The fish is popularly called Ouananiche (Lake St. John) or Sebago salmon (Nova Scotia, Quebec, New Brunswick, Newfoundland and the New England States). In Lake Vänern in Sweden there is a non-migratory form of Atlantic salmon called “blanklax”. Land-locked Atlantic salmon also occur in Lake Ladoga in Russia and in Norway in Lake Byglandsfjord. There are also land-locked Atlantic salmon in South Island, New Zealand.

What other problems affect salmon stocks?

There are a number of factors which have had an adverse effect on salmon stocks, as shown in detail on the following pages. Some, such as predation by other species, have already been mentioned. Others include:

  • Pollution of rivers and silting up of spawning gravels
  • Obstacles to migration, such as dams
  • The effect of fisheries which inadvertently take salmon (“by-catch”) or which remove the salmon’s natural food in the sea.
  • Climatic changes which are affecting the salmon’s ability to grow and survive during its time in the sea.
  • High seas and coastal “interceptory” mixed stock fisheries which take fish from more than one river population, thus denying the ability to manage the exploitation of individual river stocks on a local basis to maintain stock levels.

When do salmon spawn?

Spawning time varies between rivers and may be influenced by the water temperature and amount of daylight. Generally spawning will occur during the period November-December in Great Britain and Ireland but may extend from October until late February in our larger rivers.

How can we tell sea trout and brown trout apart?

It is sometimes quite difficult. Fresh-run, silvery, black-spotted, sea trout are obvious, but maturing specimens gradually darken on their return to fresh water, becoming more and more like brown trout.  This fact, coupled with the extensive morphological variation among brown trout, can make recognition tricky.  Normally, adult sea trout are bigger than brown trout found in the same waters, but there are many exceptions.  Male sea trout tend to lack the truly red spots found on many resident brown trout, although they often have orange ones.  Other useful indicators of brown trout, such as haloes around spots and black and white edging to fins, are not always present.  Scale reading by experts provides some scientific validation or, more certainly, biochemical analyses for levels of strontium in scales (or bones), or marine oils in tissue samples.  The species composition of internal parasites is another useful indicator of feeding at sea, but this is another test that requires the specimen fish to be sacrificed.  In practice, judgement by anglers as to whether a coloured trout is a sea trout or a brown trout must take account of the likely prevalence of sea trout in that system.

Do all sea trout undergo smolting?

No, it seems not. The process of smolting occurs in spring once a threshold size is reached and transforms relatively sedentary and highly-coloured parr which live close to hiding cover in the stream bed into free-swimming, streamlined, silvery fish, better-adapted to feeding at sea.  [Smolting is not obligatory for the transition to saline water. Non-smolting brown trout from inland sources survived and grew well when released in Norwegian fjords, indeed some brown trout strains gave better returns than most of the sea trout strains that were tested.]  Under natural conditions, most young sea trout become smolts and migrate to sea after one or more years (commonly two or three years in the UK) of growth in fresh water. However, some move down in a less advanced silvery condition, or as parr, into brackish estuaries, or sea lochs and develop into ‘ordinary looking’, or semi-silvered brown trout, the so-called slob trout, others eventually becoming fully silvered after a further period of growth.  Lastly, some smolts may not manage to migrate downriver, perhaps due to inability to get past barriers at the appropriate time for their physiological state to be maintained. These fish may revert to the appearance of ‘ordinary’ brown trout, remaining in fresh water to maturity, or they may become smolts again in the following year.

What are the main causes of the wider declines in sea trout stocks?

It is wrong to believe that sea trout stocks should remain stable. Clearly, this is not the case in natural ecosystems. Also, there are some doubts about how accurately we can assess the level of stocks. The main indicator of sea trout stock abundance remains reported catches and, while these provide a broad picture of stock abundance, they are affected by levels of reporting accuracy, weather conditions, fishing effort and new regulations etc. More importantly, the stocks upon which the catches are based are vulnerable to a wide range of habitat impacts, notably from droughts and spates, water abstraction and pollution, hydro power schemes, land drainage, nutrient enrichment and siltation and other effects of intensive farming and forestry, urbanisation, road improvements and even aggressive flood defence schemes, together with other creeping anthropogenic development of large parts of river catchments.  Increases in predation pressure on sea trout stocks by growing numbers of fish-eating birds and seals, both at sea and in our rivers, also may be an important factor.  Superimposed on all of these concerns are potentially serious effects of climate change, of increases in ambient air and water temperatures, frequency and severity of drought events and localised flash-flooding, rising sea temperature, levels and current patterns and inter-related effects on marine ecology, including changes in fish species composition and abundance.

Where do sea trout spawn?

They spawn extensively throughout river systems, normally choosing redd sites slightly earlier and in smaller streams (often 1 – 5m wide) than most salmon, although there is some overlapping of spawning timing and requirements, so that some sea trout redds can be ‘over cut’ by later-spawning salmon and grilse. [Hybridisation between salmon and trout has been shown to occur at a low level (overall about 1.0%), as detected by biochemical genetic methods.  The offspring tend to be morphologically intermediate between the parental species and thus are difficult to recognise. Fortunately, they are virtually sterile. Backcrossing to either salmon or trout is extremely rare. There is evidence from the UK and Norway that salmon which have originated in artificial culture are more likely than wild salmon to hybridise with trout.)

Do we need to protect sea trout kelts?

Mending sea trout kelts [like overwintered finnock], are very vulnerable to angling and natural predators. Unlike the case with most Atlantic salmon, where repeat spawning is fairly uncommon (generally much less than 10% of the stock), sea trout may spawn for several years, growing substantially in body weight and producing both more numerous and bigger eggs.  Therefore, sea trout kelts are especially important fish to conserve. Although by early spring those which remain in tidal estuaries may be feeding and have regained some of their lost condition, they are usually soft-bellied and lack the firm muscle that they can soon put on in a few weeks of better nourishment at sea.

Are sea trout mainly female fish?

Yes, that is normally the case.  However, male sea trout are almost as common as females in rivers where poorer environmental conditions in fresh water appear to cause most of the young fish to go to sea.  The broad picture is that females can produce both bigger and greater numbers of eggs by migrating to better feeding environments, in the case of sea trout thus enhancing the competitive value of the anadromous trait. Conversely, body size probably is less important for males, as even small males can fertilise all of the eggs of a large female.  Large, apparently physically dominant, male sea trout of similar size to the females may accompany the females, but smaller male sea trout and especially male brown trout, which are usually present nearby, often take part in the spawning acts.  This complex relationship between the sexes at spawning time is similar to the well-known participation of ripe male parr in the reproduction of Atlantic salmon. Cross-breeding of sea trout with brown trout probably helps to maintain a broad diversity of resident and migratory tactics among their progeny, leading to optimal utilisation of suitable freshwater and marine habitats.   However, even pure matings of male and female sea trout have been shown to produce juveniles that differentiate into different forms of freshwater-resident brown trout and sea trout.

Do all Atlantic salmon go to sea?

No. Although most Atlantic salmon spend part of their lives at sea there are some which are non-migratory. In several lakes in eastern North America there is a form known as a land-locked salmon, Salmo salar sebago (Girard), though their access to sea is not barred. The fish is popularly called Ouananiche (Lake St. John) or Sebago salmon (Nova Scotia, Quebec, New Brunswick, Newfoundland and the New England States). In Lake Vänern in Sweden there is a non-migratory form of Atlantic salmon called “blanklax”. Land-locked Atlantic salmon also occur in Lake Ladoga in Russia and in Norway in Lake Byglandsfjord. There are also land-locked Atlantic salmon in South Island, New Zealand.

Do salmon feed in fresh water?

As juveniles, salmon feed in their native rivers, and after smolting and migration to sea they continue to feed, principally on crustaceans and fish. Adult salmon do not feed in fresh water, although, very rarely, parr have been found in their stomachs at spawning time.

How big can sea trout grow?

Specimens weighing over 10 kgs have been caught in Scottish and Welsh rivers, but the place to find really big ones (perhaps 15+ kg) is Tierra del Fuego, at the southern tip of South America. Another area where sea trout growth is very fast and a large size can be reached is the Baltic Sea. In the UK, big sea trout can be relatively young, fast-growing, individuals (perhaps 4 – 6 years old) that have spent two or more years at sea before returning, or slower-growing, repeat spawners which have reached large size by living longer. Multiple spawning (mostly annual) is much more common among sea trout than among salmon. Prior to the 1990s, when local stocks collapsed, old sea trout weighing several kilos were common in the rivers and lochs of north-west Scotland.  Sadly, few of these fish are found there now.  In this region, both longevity and annual marine growth had fallen significantly by the end of the 1900s, with huge implications for both fisheries and egg deposition levels. However, large, young, fast-growing sea trout remain a feature of rivers entering the southern North Sea and English Channel, from rivers such as the Tweed, Coquet and Wear. Wales also remains a stronghold for fast-growing, large sea trout, some of which survive to spawn several times.

What is a grilse?

A grilse is an Atlantic salmon which has spent only one winter at sea before returning to the river. Salmon grilse are often indistinguishable from multi sea winter (MSW) salmon except by scale reading. They are smaller on average (2-3lb in May, 5-7lb in July) but when they enter rivers in September often attain 8-10lb and in October 12-15lb.

What influences the upstream movement of salmon in a river?

A number of factors affect the movement of salmon up the river. In the spring, water temperature is of great importance, and until the water temperature reaches 42ºF (5ºC) there is little upstream movement of fish over obstacles. Later in the season movement is affected by river flow and climatic conditions.

Do all salmon die after spawning?

About 90-95% of all Atlantic salmon die following their first spawning, but some survive to spawn two or three times: as many as four spawnings have been reported. The survivors, predominantly female, return to sea to feed between spawnings.

Is there just one species of salmon?

When we speak of “salmon” we are referring to either Atlantic salmon or Pacific salmon. There is only one species of Atlantic salmon: Salmo salar. There are six species of Pacific salmon: pink (Oncorhynchus gorbuscha), chum (O.keta), chinook (O.tschawytscha), coho (O.kisutch), sockeye (O.nerka) and Masou (O.masou).

Are wild salmon attacked by diseases or parasites?

Salmon, both in the wild state and in fish farms, are vulnerable to bacterial and viral diseases, and also to infestation by parasites, particularly sea lice.

A common bacterial disease is Furunculosis. The furuncles or boils, which are usually fatal, are most likely to appear in wild fish in warmer months when river levels are low and fish collect in pools while waiting for more water to allow their upstream journey to continue. It has been controlled in salmon farms by vaccination.

Ulcerative Dermal Necrosis (UDN) was rife among wild fish in the late 1960s and early 1970s. Although the causative organism has never been identified, it was almost certainly a virus. It showed itself first in the appearance of small bleached areas on the head, back and tail, which were then covered in a slimy bluish-grey growth. The affected areas were vulnerable to ulceration and infection by fungus.

Infectious Salmon Anaemia (ISA) is another viral disease to which wild fish are vulnerable; it has been endemic for some years in salmon farms in Norway, and was first detected in a number of Scottish farm sites in 1998.

Sea Lice, which can only survive in salt water, are naturally occurring parasites whose presence in small numbers indicates that a salmon in the river is fresh from sea. However, they multiply exceedingly when large numbers of farmed salmon are concentrated in sea cages, and can infest wild salmon smolts encountering them in inshore waters during their seaward migration, with highly damaging results. Sea trout smolts and adults are even more seriously affected because, unlike salmon, they spend much of their life at sea close inshore.

Gyrodactylus salaris is a skin parasite on parr. Endemic in the Baltic, where native salmon stocks are immune, it reached Norwegian rivers via local hatcheries which had received Swedish fingerlings, with devastating results, and has since been detected throughout much of continental Europe. The parasite can live for some time in damp conditions, and stringent cleaning and disinfection of fishing tackle and clothing used abroad are necessary to prevent its ingress into the United Kingdom.

How have salmon stocks changed over the years?

All around the North Atlantic, stocks have been in general decline over a number of years. Some stock components, such as early-running or ‘spring’ fish, have suffered particularly badly. Actual stock levels are difficult to estimate, except on rivers with reliable counting facilities, but catch figures can be used to give an indication, particularly of trends.

How do salmon navigate?

Salmon navigation is one of the marvels of nature. While the full answer is not yet clear, a number of mechanisms may guide salmon at sea. These include guidance by the stars as well as use of receptors sensitive to local differences in the earth’s magnetic field. Ocean currents may also play an important role. Near the coast and in the rivers, salmon are guided by a chemical memory which apparently allows them to recognise and home to substances, including pheromones, present in the water in very minute traces.

Are sea trout inclined to stray?

Although they can wander from river to river, their homing ability in terms of successful spawning appears to be very good.  The evidence for this suggestion is based on tag recapture patterns and genetic discreteness of different spawning stocks. However, some straying must occur as it was wandering sea trout during the retreat of the last Ice Age, ten to fourteen thousand years ago, that founded nearly all of the trout populations that we see in our rivers and lakes today.  Also, sea trout have spread and are now established in nearly every stream in Patagonia and the Falkland Islands after limited stocking.

How big can a salmon grow?

Atlantic salmon can grow to a very large size and the biggest, which have reached up to around 70lbs (32kg), are usually caught in Norway and Russia. However, some very large fish have been recorded in Scottish rivers. It is generally accepted that the largest one caught on rod and line in the UK was taken by Miss Georgina Ballantyne in the River Tay in 1922: it weighed 64lbs (29kg). There is an 1891 report of a huge salmon of 70lbs, also caught in the River Tay, but on this occasion in a net.

Are sea trout stocks prone to diseases and parasites?

Yes, sea trout and salmon are prone to a wide range of these pathogens because they live in both freshwater and marine environments.  Diseases and parasites are widespread and are a natural means of controlling the relative abundance of natural populations. Normally in the wild, however, sick and dying animals are soon removed by predators, or scavengers and by fungi and bacteria. Therefore, the impacts of pathogens can be hard to detect.  In contrast, the severely damaging outbreak of Ulcerative Dermal Necrosis (UDN), which occurred in the UK and Ireland in the mid-1960s, at a time of high abundance of both sea trout and salmon stocks, was very obvious. This was because of the presence in many rivers of so many dead and dying fish which were secondarily infected by fungus, although the causative agent was never fully determined.  Most disease or parasites are not normally so virulent and the rare, more obvious, outbreaks may indicate periods of stressful environmental conditions.

What is the most common age of sea trout at first spawning?

In British and Irish rivers, most sea trout seem to become sexually maturity at overall age 3+, although there is wide variation (1+ to about 6+).  Some return from the sea to spawn in their first sea year, most appear in their second, some in their third and more rarely in their fourth.  Sea age at maturity appears to be influenced by marine growth rate, but also may be affected by earlier growth pattern as parr. Mean sea age at maturity has been found to be 3 – 4 years in north Norwegian populations versus 1 – 2 years in France and Spain.

Do Atlantic salmon have a world-wide distribution?

No. Except for the land-locked varieties, they are naturally limited to the waters of countries bordering on the North Atlantic Ocean and Baltic Sea. The following countries presently have Atlantic salmon, in varying numbers: Canada, Denmark, England and Wales, Faroes, Finland, France, Greenland, Iceland, Ireland, Norway, Poland, Portugal, Russia, Scotland, Spain, Sweden, United States.

How high can a salmon jump?

The highest jump a salmon has been known to make in Scotland is a vertical one of 12ft (3.7m) at the Orrin Falls in Ross-shire. The height a salmon can achieve depends upon the relative depth of the water at the foot of the fall and the position of what is referred to in engineering terms as the “standing wave” or hydraulic jump.

Why are some rivers good for sea trout while others are not?

Sea trout probably occur in every river where there is access to and from the sea.  Their relative abundance in each seems to be linked with a balance of advantages and disadvantages of the various traits that the local trout may adopt. Intuitively, richer, slower-flowing rivers should favour freshwater residence; low-nutrient, spatey rivers should favour sea trout.  However, it isn’t that simple. The overall production of sea trout smolts may be greater in richer rivers than in poor ones, although a smaller proportion of the juvenile trout may migrate to the sea from rich rivers.  Variation in marine conditions also must be taken into account.  If growth and survival levels for sea trout at sea are persistently low, the anadromous trait may be a poorer option than one of freshwater residence and will be selected against. On the other hand, if the post-smolts encounter rich marine feeding and grow big, the returning females carrying many eggs, the sea trout fraction may flourish.

How many eggs do sea trout produce?

There is quite a lot of variation, although the theoretical average figure of 800 eggs per pound of body weight has been cited in the past.  Overall, British and Norwegian stocks of sea trout have similar levels of fecundity, but French sea trout produce many more eggs for the same body size. It is unclear how much of this natural variation is inherited and how much it depends on early growth rate, overall age and levels of feeding at sea.  In Scotland, River Ewe System (Wester Ross) sea trout contain significantly fewer (but larger) eggs than River Earn (East Coast) sea trout of the same size.  Unlike in birds, egg size in trout increases with overall body size, but it also increases with age, independently of body size. So, large, old sea trout produce the biggest eggs, while smaller, but fast-growing, young sea trout have lots of small ones.  The early survival prospects of fry may be positively linked with egg size, but many other factors come into play in deciding their fate.

When do sea trout come up our rivers?

The timing of upstream migration varies among regions. In Scotland, early-running sea trout stocks ascend some of our larger river systems from about April through to early June.  These fish are more likely to have originated within headwater streams.  Lower tributaries often are populated more by later-running fish, some coming into the rivers so late that angling is closed.  Early-running sea trout at first are relatively easily caught by angling as they move upriver.  Soon they settle down for the summer in accessible lochs (lakes) or, often in rivers, in slow, deeper pools, hiding during daylight hours under overhanging banks or tree cover, or overhead water turbulence, jumping and moving more during and after dusk.  Smaller in body size on average than most salmon, they have a tendency to progress upriver during the hours of darkness at times through remarkably shallow water.  In the absence of automatic fish counters and video equipment sited at key points of passage, adult sea trout stock abundance is difficult to estimate.

What are grilse?

A grilse is an Atlantic salmon which has spent only one winter at sea before returning to the river.

Are stocks of sea trout, well away from the influence of salmon culture, also declining?

The First International Sea Trout Symposium, held in Cardiff, July 2004 (Harris and Milner, 2006) found that stocks were apparently healthy in some regions and countries, but weak in others.  In the UK, there has been in a dramatic increase in catch and release of sea trout (and salmon) over the past ten years, helped by a combination of conservation measures, byelaws, voluntary agreements, club rules, incentive schemes and angler awareness. While greatly to be applauded, these measures have complicated interpretation of the national catch statistics in comparison with earlier decades.  However, there is a growing concern, based not only on catches but on sightings by experienced observers, that sea trout numbers have fallen to low levels in several areas of the country distant from threats of salmon farming, although not to the extent of the population collapses that have occurred in the north west of Scotland and the west of Ireland.

What else can be done to address the decline of sea trout stocks?

Basically, stop killing so many sea trout and act now to restore and protect their habitat. Fishery owners and managers, fishery boards, trusts etc have to decide whether there is a harvestable surplus in their waters and regulate fisheries accordingly. Control of exploitation by nets and catch and release by anglers can make a substantial difference to fish size, abundance and population fecundity in future generations. Government environmental agencies now have stronger powers, through the E.U. Habitats and Water Framework Directives, to mitigate many environmental problems. Even so, the continuing growth in human numbers, aspirations and social expectations seriously threaten the future quality and quantity of fresh water. Nor can anyone predict with certainty how precious freshwater and marine resources will be affected by ever-changing climatic conditions. Sea trout stocks provide a very important economic and social asset. Their status is a sensitive barometer of the continuing health of the arterial systems of our rivers and our coastal seas.  We are urgently in need of more research directed towards sensitive and well-informed measures to assist in their conservation and fishery management.

Time course of the salmon’s acclimation responses?

The behavioral (drinking or not drinking) and physiological changes a salmon must make when moving from fresh water to salt water — and vice versa — are essential, but cannot be accomplished immediately. Thus, when a young salmon on its seaward journey first reaches the saline water at the mouth of its home stream, it remains there for a period of several days to weeks, gradually moving into saltier water as it acclimates. During this time, it begins drinking the water it’s swimming in, its kidneys start producing a concentrated, low-volume urine, and the NaCl pumps in its gills literally reverse the direction that they move NaCl (so that they’re now pumping NaCl out of the blood and into the surrounding water.
Likewise, when an adult salmon is ready to spawn and reaches the mouth of its home stream, it once again remains in the brackish ( i.e. less concentrated than full-strength sea water) water zone of the stream’s mouth until it is able to reverse the changes it made as a juvenile invading the ocean for the first time.

How Does The Salmon Solve Its Osmoregulatory Problems?

Fortunately, the salmon has some remarkable adaptations, both behavioral and physiological, that allow it to thrive in both fresh and salt water habitats. To offset the dehydrating effects of salt water, the salmon drinks copiously (several litres per day). But in fresh water (where water loading is the problem) the salmon doesn’t drink at all. The only water it consumes is that which necessarily goes down its gullet when it feeds. Of course, when an ocean-dwelling salmon drinks, it takes in a lot of NaCl, which exacerbates the salt-loading problem. Kidney function also differs between the two habitats. In fresh water, the salmon’s kidneys produce large volumes of dilute urine (to cope with all of the water that’s diffusing into the salmon’s body fluids), while in the ocean environment, the kidneys’ urine production rates drop dramatically and the urine is as concentrated as the kidneys can make it. The result of this is that the salmon is using relatively little water to get rid of all of the excess ions it can.

What is osmoregulation?

Osmoregulation is the control of the levels of water and mineral salts in the blood. All fish which migrate from fresh water to salt water during their life cycle must go through this process.

The salmon is an excellent osmoregulator. However, like virtually all osmoregulators, the salmon is never in true equilibrium with its surroundings. In the ocean, the salmon is bathed in a fluid that is roughly three times as concentrated as its body fluids, meaning that it will tend to lose water to its surroundings all of the time. And, because the composition of its body fluids is so different from the ocean water, the salmon will be faced with all manner of gradients that are driving exchanges that will continuously tend to drive its body fluids’ concentration and composition beyond homeostatic limits. In particular, the very high concentration of NaCl (sodium chloride) in the ocean water relative to its concentration in the salmon’s body fluids will result in a constant diffusion of NaCl into the salmon’s body. Unless dealt with effectively, this NaCl influx could kill the salmon in a short time. In sum, a salmon in the ocean is faced with the simultaneous problems of dehydration (much like a terrestrial animal) and salt loading.
However, in fresh water, the problem is basically reversed. Here, the salmon is bathed in a medium that is nearly devoid of ions, especially NaCl, and much more dilute than its body fluids. Therefore, the problems a salmon must deal with in fresh water environments are salt loss and water loading.

Why and where are sea lice believed to be serious parasites of sea trout?

Sea lice (mainly the salmon louse, Lepeophtheirus salmonis (L.)) are naturally occurring and widespread skin parasites of salmon and sea trout in their marine phases. Other lice (Caligus spp.) also can be found on sea trout and salmon at sea, but are more common on other fish species. At the low background levels of infection found in areas away from marine salmon culture, Leps. cause sea trout few problems.  However, coastal rearing of salmon in net cages leads to a sharp increase in the potential for louse infestation. Given that these parasites are extremely well-adapted to finding and attaching to their normally relatively scarce salmonid hosts, it is unsurprising to find that in areas of intensive salmon culture louse infection levels can become very heavy on coastal sea trout post-smolts.  [Wild salmon post-smolts are vulnerable too, less so those than can migrate out quickly to the open sea.]  Sadly, recent history, in Scotland Ireland and Norway, has shown that marine mortality levels soon escalate among sea trout that migrate into bays or sea lochs containing salmon farms and their spawning stocks may collapse.  Control of sea lice on the farms has improved lately, but is still largely limited to chemical treatment within the cages and the use of fallow periods after the salmon reach a marketable size in order to limit opportunity for cross-infection between cage sites and age groups.  Inevitably, there is a tendency for the lice to develop immunity to the few lice removing chemicals that are sanctioned for use.  In recent years, better control of sea lice has been achieved through the use of SLICE, but this may be only a temporary success as resistance to the treatment has already been detected. Under the present prevalent rearing regime involving open cages, there is an urgent need for new chemicals to be found regularly, their efficacy and safe use examined and authorised.  [In the longer term, through local and international agreements, commercial salmon culture may have to move to totally enclosed onshore rearing facilities].

What do sea trout feed upon at sea?

They are opportunistic feeders and consume a wide range of marine organisms, from small crustaceans taken from the seabed and midwater to fish such as sandeels, sprats and juvenile herring.  Early post-smolts can even be seen feeding at the surface of Scottish sea lochs on wind-blown terrestrial flies. Rapid growth seems to be associated with a quick transition to feeding upon fish.  Seasonal prey abundance and quality may be key components affecting marine growth and survival of sea trout.

Where do smolts go?

Smolts are believed to move in schools while heading off to deep-sea feeding areas. While the best-known feeding locations are in the Norwegian Sea and the waters off Southwest Greenland, there are known to be many other sub-arctic feeding areas. Salmon that remain at sea for more than one winter undertake the longest migrations, but grilse tend not to travel beyond the Faroe Islands and the southern Norwegian Sea.

How closely do sea trout relate to brown trout which remain in fresh water?

The broad species that we call brown trout occurs in a wide range of forms differing in average size, in colouration and spot pattern, diet and migratory behaviour. Some live only in streams; others migrate to find better space and feeding in lakes or larger rivers, in estuaries, or in the sea.  Sea trout become silvery smolts before or during migration to sea, but so do some strains of brown trout that migrate only as far as shallow freshwater lakes, for instance Loch Leven, Kinross-shire, in Scotland.

What are the salmon’s natural enemies?

At different life stages, the principal predators of salmon are goosanders and red-breasted mergansers, cormorants, gulls, pike, pollack, cod, sharks, seals and otters.

What factors influence which young trout become smolts and migrate to sea?

The process is not yet fully understood. Although there is strong evidence from scientific studies indicating a genetic basis to the seagoing tendency, the rearing environment also has been shown to be important. For example, artificial rearing of sea trout progeny can increase the proportion that remains in fresh water.   Incubation of the eggs at water temperatures differing from natural cyclic levels and improved food availability for the fry and parr held in tanks, providing a ‘soft’ life-style  compared with life in the wild, can change normal seasonal patterns of growth and advance the onset of sexual maturity, favouring the adoption of resident over migratory behaviour.

What is a sea trout?

The sea trout is the anadromous (sea-going) form of the European brown trout (Salmo trutta. L.). It is native to western Europe from northern Portugal to the White Sea and Cheshkaya Gulf, Iceland and the Baltic Sea and has been established relatively successfully in eastern North America, but more so in the Southern Hemisphere, in Patagonia and the Falkland Islands, New Zealand and Australia/Tasmania.

What is a finnock?

Finnock (otherwise locally named whitling, herling, school peal, harvesters etc) are small sea trout in their first year after smolt migration, often found in the estuaries or lower areas of rivers.  They do not necessarily remain faithful to their natal areas at this stage, instead they range widely up and down coasts, moving into and out of fresh water with the tides.  Often congregating at “choke points” around estuaries, they are highly vulnerable to excessive angling pressure, as well as natural predation.  Many of these attractive and energetic fish may over-winter in fresh water while still immature, making only limited growth until they return to the sea properly in spring.  Why they do this and lose potential growing time utilising richer marine feeding is unknown.  It seems unlikely to be an avoidance response to osmotic problems because salinity tolerance trials have shown that even small post-smolt sea trout have no apparent problems coping with full-strength seawater, in summer or winter.  While finnock are characteristic of the rivers further north, the prolific sea trout rivers of south-east Scotland and north-east England largely lack this early-returning itinerant form.  [The term “Whitling” is also used on the River Till in Northumberland, a lower tributary of the Tweed.  Here it refers to small sea trout, mostly of 1+ sea winters]. Tagging has shown that many of the post-smolt trout from the Rivers Tweed and Coquet move down the North Sea and remain there during winter, taking full advantage of the rich potential for feeding.  These further-travelling, faster-growing sea trout appeared historically in netting catches off the Northumberland and Yorkshire coasts, then East Anglia, Holland and Denmark, before returning to their native rivers to spawn. The erratic movements of finnock between rivers in general and the extensive migrations of sea trout in the southern North Sea indicate significant mixing of stocks during the marine phase, raising complex issues for their conservation and fishery management.

What does anadromous mean?

The Atlantic salmon and sea trout is referred to as being anadromous because of its habit of migrating from the sea into fresh waters to spawn. This is the exact opposite of the common eel which leaves fresh waters to spawn in the Sargasso Sea, and is therefore called catadromous.

Can male and female salmon easily be identified?

When they arrive fresh from the sea it is difficult to distinguish the sex of salmon externally. Later the head of the male becomes elongated and grows a protuberance called a “kype” from the tip of the lower jaw. At this stage male and female are easily distinguished.

What are the main predators of sea trout?

They have many natural predators at all stages of the life cycle, ranging from various fish-eating birds, eg. saw-billed ducks and terns, which attack the smolts gathering in lower rivers and estuaries and the post-smolts in their early life at sea, to gadoid fish such as pollack and cod and pelagic dogfish, then they must pass through areas frequently inhabited by common and grey seals. Back in fresh water, mink and otters take a proportion of sea trout, as occasionally do ospreys and, in some rivers, pike. Humans have the potential to take many more.

What do sea trout eat?

It is generally accepted that, once they return to the river to spaw,. sea trout do not eat, but live on the reserves they have built up. While at sea, sea trout feed on prey items such as small crustaceans, marine worms, sandeels (Ammodytes spp.), sand smelts (Atherina sp), sprats (Clupea sprattus), juvenile members of the cod family, sticklebacks, sand goby (Pomatoschistus spp.) and terrestrial insects. Larger fish tend to consume larger prey items.

Is stocking an answer to declining sea trout stocks?

No. There are deep genetic concerns over the impact of stocking on wild salmonids populations, largely through a loss of population ‘fitness.’ Where, after careful consideration of other options, stocking can be justified, it needs to be carried out using the offspring of native broodstock, a procedure known as ‘supportive breeding.’ The period in the hatchery should be as short as possible commensurate with overcoming the natural ‘bottleneck’ in production e.g. loss of spawning habitat.  It is important that rearing is carried out in such a manner so as not to result in inbreeding and loss of genetic variability, or inadvertent selection.

Is the growth of salmon farming significant for wild salmon and sea trout stocks?

Farmed salmon production in the North Atlantic area has increased dramatically, particularly in Norway, but also on the west coasts of Ireland and the Scottish Highlands.

A number of problems have resulted, which include:

  • High concentrations of sea lice, which multiply in the confined conditions of sea rearing cages. As explained earlier, migrating sea trout and salmon smolts can be very vulnerable to attack by these lice. In some rivers, wild stocks have virtually collapsed.
  • Escapes of farmed fish, which are known to be able to interbreed with wild fish. Since stocks in individual rivers are locally adapted to optimise their survival, this interbreeding has been shown to reduce the fitness of wild stocks for their local environment.
  • Pollution of the water environment, by uneaten food, fish faeces, or medications used to treat farmed salmon in their cages.
  • The risk of the spread of disease or parasitic infestation, such as Infectious Salmon Anaemia and Gyrodactylus salaris.

What is a salmon smolt?

Salmon remain in their natal stream as parr for one to three years before becoming smolts, which are distinguished by their bright silvery colour with scales that are easily rubbed off. It is estimated that only 10% of all salmon eggs survive to this stage. The smolt body chemistry changes, allowing them to live in salt water. Smolts spend a portion of their out-migration time in brackish water, where their body chemistry becomes accustomed to life in the ocean via the process of osmoregulation.

What do salmon feed on in the sea?

The salmon feed on a variety of small fish including capelin, herring, sand eels and sprats and the larger animals found in plankton, especially surface-living crustaceans.

When do the salmon’s eggs hatch?

The incubation time depends upon the water temperature. Hatching usually occurs in early spring and the young fish (called “alevins”) remain in the redd for a few weeks., nourished by the attached yolk sac. When they emerge from the gravel in April or May, they are about one inch in length. As they grow, the young fish develop prominent markings on their sides and are then known as parr.

What should fishermen look out for particularly in connection with any salmon or sea trout they catch?

Biologists who work with salmon and sea trout often mark the fish that pass through their hands in any of the ways depicted below. Capture of a marked salmon should be reported at once to the appropriate fishery authority. Frequently the address is on the tag or mark. Usually the information required is: date, place and method of capture; length, weight and sex of fish and a sample of scales taken from between the dorsal and anal fins at above the lateral line.

How long do salmon stay at sea?

They remain in the ocean from just over a year to three or four years. Salmon feeding off Greenland generally stay at sea for two or three years.

Where are the salmon’s eggs deposited?

They are laid in depressions called “redds” excavated by the female fish in the gravel of the river bottom. After the eggs are deposited they are immediately fertilised by an accompanying sea-run male, and often by mature male parr, and then covered with gravel by the female.

How big can salmon grow?

Atlantic salmon can grow to a very large size and the biggest, which have reached up to around 70lbs (32kg), are usually caught in Norway and Russia. However, some very large fish have been recorded in Scottish rivers. It is generally accepted that the largest one caught on rod and line in the UK was taken by Miss Georgina Ballantyne in the River Tay: it weighed 64lbs (29kg). There is an 1891 report of a monster salmon of 70lbs, also caught in the River Tay, but on this occasion in a net belonging to a Mr. Speedie.


How do I tell the difference between a Salmon and a Sea-Trout?

Well Sea-Trout tails are square and thick at the wrist whilst Salmon tails are concaved and slender at the wrist. Spots on a sea-Trout continue below the lateral line whilst Salmon have fewer spots below the lateral line. The eyes on a Sea-Trout are further forward in the head than the Salmon. Finally if you’re still unsure count the scales between the adipose fin and the lateral line, a count of less than twelve, it is a Salmon, more than twelve and it’s a Sea-Trout.