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charset=UTF-8"/> <link rel="shortcut icon" href="https://web.archive.org/web/20111130201523im_/http://www.atlanticsalmontrust.org/favicon.ico"/> <title>The Atlantic Salmon Trust - Salmon Facts</title> <meta name="description" content="The Atlantic Salmon Trust's extensive collection of information and knowledge about the atlantic salmon."/> <meta name="keywords" content="Atlantic salmon, sea trout, conservation, knowledge, salmo salar, salmo trutta"/> <link href="/web/20111130201523cs_/http://www.atlanticsalmontrust.org/styles/ast.css" rel="stylesheet" type="text/css"/> <script type="text/javascript" src="/web/20111130201523js_/http://www.atlanticsalmontrust.org/scripts/jquerycore.js"></script> <script type="text/javascript" src="/web/20111130201523js_/http://www.atlanticsalmontrust.org/scripts/ast.js"></script> </head> <body> <div id="wrapper"> <div id="header"> <div id="logo"> <a href="/web/20111130201523/http://www.atlanticsalmontrust.org/" title="Back to our Homepage"><img src="/web/20111130201523im_/http://www.atlanticsalmontrust.org/images/atlantic-salmon-trust-logo.jpg" width="150" height="150" alt="The Atlantic Salmon Trust" border="0"/></a> </div> <div id="headline"> <div id="headline1">The Atlantic Salmon Trust</div> <div id="headline2">Funding research and practical measures to ensure<br/>the future of salmon and sea trout at sea and in fresh water</div> <div class="headersignup"><a href="/web/20111130201523/http://www.atlanticsalmontrust.org/newsletter/" class="headiconlink">Sign-up for our<br/>Newsletter</a></div> <div class="headerdonate"><a href="/web/20111130201523/http://www.atlanticsalmontrust.org/donations/" class="headiconlink">Donate Now</a></div> </div> </div> <div id="menuwrapper"> <div id="menudiv"> <div id="menu0"><a class="menulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/">Home</a></div> <div id="menu1"><a class="menulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/who-we-are/index.html">Who We Are</a></div> <div id="menu2"><a class="menulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/research/index.html">Research</a></div> <div id="menu3"><a class="menulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/latest-news.html">Latest News</a></div> <div id="menu31"><a class="menulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/events.html">Events</a></div> <div id="menu4"><a class="menulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/questions-and-answers.html">Q&As</a></div> <div id="menu5" class="menuactive"><a class="menulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/knowledge/index.html">Knowledge</a></div> <div id="menu6"><a class="menulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/concerns/index.html">Key Issues</a></div> <div id="menu7"><a class="menulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/how-you-can-help/index.html">How You Can Help</a></div> <div id="menu8"><a class="menulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/information/contact-us.html">Contact</a></div> <div id="menu9" class="menuitemlast"><a class="menulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/information/learning-zone.html">Learning Zone</a></div> </div> </div> <div id="subleftwrapper"> <div class="borderedwrapper"> <div class="sidetitle"> Salmon & Sea Trout - Knowledge </div> <div class="sidemenuitem"> <a class="submenulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/knowledge/salmon-and-sea-trout-status-reports.html">Salmon & Sea Trout status reports</a> </div> <div class="sidemenuitemlive"> <a class="submenulinklive" href="/web/20111130201523/http://www.atlanticsalmontrust.org/knowledge/salmon-facts.html">Salmon Facts</a> </div> <div class="sidemenuitem"> <a class="submenulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/knowledge/sea-trout-facts.html">Sea Trout Facts</a> </div> <div class="sidemenuitem"> <a class="submenulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/knowledge/the-salmons-lifecycle.html">The Salmon's Lifecycle</a> </div> <div class="sidemenuitem"> <a class="submenulink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/knowledge/salmon-and-sea-trout-recognition.html">Salmon and Sea Trout Recognition</a> </div> </div> </div> <div id="subdoublewrapper"> <div id="subcontentstitle"> Salmon Facts </div> <div id="subcontents"> </div> <div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump73"><strong>Q. What is osmoregulation?</strong></div><div><p><span style="color: #000000;"><strong><strong></strong></strong></span><span style="color: #000000;">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. <br/></span></p> <p>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 <em>composition</em> 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 <em>into</em> 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.<br/>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.</p> <p><strong>How Does The Salmon Solve Its Osmoregulatory Problems?<br/></strong>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.<br/>         <br/> <strong>Time course of the salmon's acclimation responses<br/></strong>The behavioral (drinking or not drinking) and physiological changes a salmon must make when moving from fresh water to salt water — and <em>vice versa</em> — 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 <em>out of</em> the blood and into the surrounding water. <br/>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.</p> <p><strong></strong></p> <p><strong></strong><strong><strong>  </strong></strong><strong></strong><strong><strong></strong></strong></p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump1"><strong>Q. Do all Atlantic salmon migrate to sea?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump2"><strong>Q. What is a grilse?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump3"><strong>Q. How big can a salmon grow?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump7"><strong>Q. What is the largest Atlantic salmon ever recorded?</strong></div><div><p>The largest recorded Atlantic salmon, a male caught in Norway’s Tana River, weighed 35.89 kg. and was over 150 cm. in length.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump8"><strong>Q. How have salmon stocks changed over the years?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump9"><strong>Q. What other problems affect salmon stocks?</strong></div><div><p>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:</p> <ul> <li>Pollution of rivers and silting up of spawning gravels</li> <li>Obstacles to migration, such as dams</li> <li>The effect of fisheries which inadvertently take salmon ("by-catch") or which remove the salmon's natural food in the sea.</li> <li>Climatic changes which are affecting the salmon's ability to grow and survive during its time in the sea.</li> <li>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.</li> </ul></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump12"><strong>Q. Are wild salmon attacked by diseases or parasites?</strong></div><div><p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump13"><strong>Q. What do salmon feed on in the sea</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump15"><strong>Q. Do salmon feed in fresh water?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump16"><strong>Q. What influences the upstream movement of salmon in a river?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump17"><strong>Q. How high can a salmon jump?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump18"><strong>Q. What are the salmon's natural enemies?</strong></div><div><p>At different life stages, the principal predators of salmon are goosanders and red-breasted mergansers, cormorants, gulls, pike, pollack, cod, sharks, seals and otters.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump19"><strong>Q. How long do salmon stay at sea?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump20"><strong>Q. What are grilse?</strong></div><div><p>A grilse is an Atlantic salmon which has spent only one winter at sea before returning to the river.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump21"><strong>Q. Where do smolts go?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump22"><strong>Q. When do salmon leave the river?</strong></div><div><p>The young fish, now called "smolts", leave the rivers during the late spring. Most will be gone by June.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump23"><strong>Q. How long do young Atlantic salmon stay in the river before migrating to sea?</strong></div><div><p>This is dependent upon the water temperature and the availability of food. The length of stay varies very much, from one year in the southern portion of the salmon's range to five or more years in the more northern, colder regions.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump24"><strong>Q. When do the salmon's eggs hatch?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump25"><strong>Q. Where are the salmon's eggs deposited?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump26"><strong>Q. How many eggs does an Atlantic salmon deposit?</strong></div><div><p>Female salmon in most areas produce 450-750 eggs per pound of body weight but the number may rise, for example in Iceland, to 900.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump27"><strong>Q. Do all salmon die after spawning?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump28"><strong>Q. When do salmon spawn?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump29"><strong>Q. Can male and female salmon easily be identified?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump30"><strong>Q. Do salmon always return to their own river?</strong></div><div><p>Atlantic salmon return to their native river with amazing accuracy. Although some may stray to other rivers, the majority ascend their home river.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump31"><strong>Q. How do salmon navigate?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump32"><strong>Q. Do Atlantic salmon have a world-wide distribution?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump33"><strong>Q. How big can salmon grow?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump34"><strong>Q. Do all Atlantic salmon go to sea?</strong></div><div><p>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.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump37"><strong>Q. What is an Atlantic Salmon?</strong></div><div><p>The Atlantic salmon (Salmo salar) is an anadromous migratory fish found in the temperate and arctic regions of the Northern Hemisphere.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump41"><strong>Q. How does one know the age of a salmon?</strong></div><div><p>The concentric rings of the scales of a salmon can reveal the age of a fish. When the young salmon first emerges from the gravel it has no scales, but very soon papillae start to appear along each side and develop quickly into small calcareous plates which, as they grow, lay down rings or 'circuli' at regular intervals. During periods of rapid growth occurring in the warmer months, when the fish are feeding more actively, the rings are widely spaced, but during the winter months when feeding activity is reduced, the circuli are laid down close together, giving the appearance under the microscope of a dark band, known as an 'annulus'.</p> <p>The annulus is complete by the end of the period of little or no feeding in the winter. Once feeding recommences in the late spring the circuli are again more widely spaced. So by counting the 'annuli' or winter bands, the age of the fish can be determined.</p> <p><img title="Salmon scale detail" src="/web/20111130201523im_/http://www.atlanticsalmontrust.org/assets/salmon-scale.gif" alt="Salmon scale detail" width="300" height="221"/></p> <p>An illustrated example of a grilse scale - age 2.1+ (two years in the river and over one year in the sea)</p> <p>R = River life<br/>S = Sea life<br/>F = Focus of scale or nucleus</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump42"><strong>Q. How can salmon be recognised at the different stages of their life in fresh water?</strong></div><div><p><img title="Fresh run salmon" src="/web/20111130201523im_/http://www.atlanticsalmontrust.org/assets/fresh-run-salmon.jpg" alt="Fresh run salmon" width="560" height="183"/></p> <p><strong>Fresh-Run Salmon</strong><br/>Recognised by the pristine condition and bright silver flanks. Fish straight from salt water have loose, easily detached scales and many carry sea lice which drop off within a few days. Hen salmon (illustrated) have a tiny kype on the lower jaw but unlike cocks they retain normal head proportions while in the river.</p> <p><img title="Maturing salmon" src="https://web.archive.org/web/20111130201523im_/http://www.atlanticsalmontrust.org/assets/maturing-salmon.jpg" alt="Maturing salmon" width="556" height="316"/></p> <p><strong>Maturing Cock and Hen</strong><br/>Cock: The combination of "tartan" colours is typical although shades vary - the fully developed kype, used in fighting rivals, and the enlarged adipose fin, are the most consistent indicators of maturity.</p> <p>Hen: These are usually less coloured than cocks of similar age and they never have enlarged jaws. This one will have spent a few weeks in river or estuary - note the coloured head and lack of true silver flanks.</p> <p><img title="Spawning salmon" src="https://web.archive.org/web/20111130201523im_/http://www.atlanticsalmontrust.org/assets/salmon-in-breeding-dress.jpg" alt="Spawning salmon" width="579" height="320"/></p> <p><strong>Cock and Hen In Breeding Dress<br/></strong>Cock: The combination of 'tartan' colours is typical although shades vary - the fully developed kype, used in fighting rivals is the most consistent indicator of maturity.</p> <p>Hen: This is a summer fish - springers are often darker by spawning time while late entrants may still be silver flanked. Fully mature hens have soft, swollen bellies and spawning is imminent if they also have protruding vents.<strong></strong></p> <p><img title="Salmon kelt" src="/web/20111130201523im_/http://www.atlanticsalmontrust.org/assets/kelt.jpg" alt="Salmon kelt" width="566" height="169"/></p> <p><strong>Kelt</strong><br/> Kelts are salmon which have spawned. Usually identified by the thin shape, distended vent and presence of "gill maggots" on the red gill filaments, they are often encountered by anglers in spring when they regain a silvery appearance and can be mistaken for fresh run Springers. Kelts must be returned unharmed to the water.</p></div></div><div class="borderedwrapper"><div style="margin:0 0 5px 0;" id="jump35"><strong>Q. Is there just one species of salmon?</strong></div><div><p>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).</p></div></div> </div> <div id="mainclear"> </div> <div id="footer1"> <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/index.html">Home</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/who-we-are/index.html">Who We Are</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/research/index.html">Research</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/latest-news.html">Latest News</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/questions-and-answers.html">Questions and Answers</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/knowledge/index.html">Knowledge</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/concerns/index.html">Key Issues</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/how-you-can-help/index.html">How You Can Help</a> <br/> <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/information/learning-zone.html">Learning Zone</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/information/contact-us.html">Contact Us</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/information/useful-links.html">Useful Links</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/information/shop.html">Shop</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/information/terms-and-conditions-privacy.html">Terms & Conditions / Privacy</a> |  <a class="footerlink" href="/web/20111130201523/http://www.atlanticsalmontrust.org/sitemap.html">Site Map</a>  |  <a class="footerlink" href="https://web.archive.org/web/20111130201523/http://newsletter.astnews.org.uk/?p=subscribe" target="_blank">Sign Up for Our E-Newsletter</a> </div> <div id="footer2"> The Atlantic Salmon Trust ©2011 - 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