A key resource has been the Atlantic Salmon Trust, where both visual and written references are readily available.

Salmon Parr

Salmon emerge from eggs in freshwater rivers, such as the Wye.  Until they absorb their egg sacs their known as alveolin.  After, they’re called fry.  If they escape predation and grow to about 2inches long, they are called Parr.  Sometimes they’re called or Fingerlings.

Salmon parr

A Salmon parr needs to escape predation.  So it develops camaflauging “parr marks” (bands of colour) across their backs.  These break up their shape and help the fish avoid being eaten by heron, mink, goosander, and other fish such as trout.

There is often confusion within the angling community when it comes to distinguishing between Salmon and Brown Trout (Salmo trutta) as the two species closely resemble each other.  With the young Parr, the main differences are that the salmon has a more streamlined shape, a deeper fork to its tail, a longer pectoral fin, a sharper snout and smaller mouth than a young Trout, and has no orange on the adipose fin (at the rear, to the back)

A Salmon Parr will only sport a couple of spots on its gill cover (often just one large spot), and its parr or fingerling markings are quite crisply defined.

Salmon smolt

After a couple of years of living in freshwater, the young salmon undergoes some major alterations to its body and chemistry which enable it to migrate to the salty waters of the Atlantic Ocean where the fish will feed amd grow.  These changes are called “smoltification” and occur in esturine waters where the young fish gather in shoals before setting out to the open sea.

Visually, the change from a Parr to a Smolt is primarily a loss of the stripes seen on a parr, and a change of colour as the fish becomes silvery.  This is caused by guanine crystals which form a layer in the skin and obscure the spots and fingerling markings (although these are still visible on the gill covers).

Salmon smolt

Their bodies elongate and their fins darken.  The silvery scales can be rubbed off easily.  It’s hard to distinguish between the sexes until the males became ready to breed.

Adult salmon

As adults, the Salmon will return to the freshwater of their birth to breed.  When they first appear, as “Fresh Run Salmon” both sexes are bright silver and pretty similar, with easily detachable scales.  You can often tell how long an adult salmon has been in fresh water by the birghtness of its silver colouring, and from the sea lice which die when their hosts switch from salty to fresh water.  A silvery adult with near complete sea lice in situ will have only just left the marine environment; one with less of a gleam and more degraded (or without) sea lice is likely to have been back in the river for longer.

Hen Salmon

The adult female fish will retain more of this silver colour than the male, although being in fresh water will cause her scales to darken, and she will develop a tiny kype or bump on her lower jaw.

Fresh run Hen Salmon

A female adult salmon is known as a Hen, a male is known as a Cock.

Cock salmon

Once in breeding colours it’s easy to recognise a Cock salmon.  The two main features are the change in colour and of the lower jaw. A breeding male’s colouration is often described as a tartan pattern, and means the fish is patchy with different shades of oranges, silver, and red markings.  Overall the fish is brownish-orange, pinkish-red, or yellowish in colour.  There’s plenty of variation between individuals.  The lower jaw develops a prominent hook or “kype” which is used to fight rivals who threated its teritory.  It also makes eating almost impossible; adult salmon mostly die after mating.

Cock salmon with kype

The Cock salmon will also have an enlarged adipose fin.

Salmon vs Trout

Again, there’s occasional confusion between an adult salmon and a large adult brown trout.  The Salmon have a more streamlined shape, a concave tail with a thinner neck than the trout tail, far fewer (or no) black spots below the lateral line (about half way down the fish body), and its upper jaw tends not to reach any further back than the rear of the eye.  Obviously, wiht an adult cock salmon with kype and tartan pattern, the difference us clear and immediate.

Adult Brown trout Salmo trutta

One more stage in the life cycle of a salmon is that on the kelt (not illustrated).  Kelts are salmon which have spawned but still remain in the river.  They regain a more silvery colour but are noticably thin, with a distended vent and frequently have red “maggots” on their gills.

A hen salmon will use her tail to scrape a nest or “redd” in the pebbles and lay eggs which are fertilized by the male, cover them over, deposit more eggs on top, cover them, and so on.  In time these will hatch into tiny salmon fry and so the cycle begins again.

For more information, please check out the Cornwall Rivers website, or teh Atlantic Salmon Trust.  For more on this project, look at my blog on the Glanwye project.

The post Natural History Illustration: Salmon life cycle appeared first on Lizzie Harper.

I enjoyed the whole day enormously.  I learnt a tremendous amount, especially about insects, thanks to the endless knowledge and enthusiasm brought by Phil Ward of RWT.   Phil also happens to be the entomological recorder for the county.  I now know my reed beetle, dock beetle, and upland click beetle (a beauty).   I have got a lot better at spotting animals of all descriptions; including little froglettes which we encountered repeatedly.

How to look for freshwater life

Towards the end of this extremely interesting and enjoyable day, we took on the task of seeing what was living in the stream that runs through the reserve.  We did this by stirring up a prescribed length of stream (which related to the stream width) for exactly three minutes. We caught everything we disturbed.  Going through the finds and identifying them to family level came next.  (Further classification to genus or species was done by Phil Ward and other keen entomologists later on).

Searching for fish

We were surprised not to find any bullhead fish as they’re common in streams such as this one.  The reserves manager for RWT was keen to see if we could spot any fish at all – to no avail on this occasion, bar one tiny fry.

Freshwater life: Invertebrate variety

However, the invertebrate life we gathered was vibrant, diverse, and fascinating.  The number of mayfly nymphs was amazing.   This is encouraging.  They tend to thrive only in very clean and oxygenated streams.   We learnt that the larva can be burrowing, free-swimming, or live flattened against rocks.  Nymphs graze on plants or algae; the burrowers may feed on silt in the mud.  The adults have no mouth parts and all emerge simultaneously.  No-one is sure why, but the final stage of mayfly nymphs emerge from the water, and are able to fly, before they turn into mature adults.

We found many different caddis fly larvae; some had built pebbly homes flat on the underside of stones; others had constructed intricate turrets from tiny grains of sand,; others had cobbled together a home from pebbles, and another species favoured snippets of twig, all laid vertically together, to make their homes.  Each type of case was created by a different species of caddis fly larvae.

We also found stonefly nymphs, and alderfly larva (who differ in appearance to mayflies in having a single, feathery tail rather than three long tails).  Freshwater shrimp were in evidence too.

Follow up: Looking for Freshwater Life in a local stream

Fired up by this day out, I immediately became a family member of RWT, then I ordered a whole clutch of fold-out charts, produced by the Field Studies Council.

Thus armed, I went stream dipping a little closer to home, in the little river Edw near Erwood in Powys, and found some new organisms as well as caddis fly and mayfly nymphs.  The most fascinating were the leeches.  Only one species of leech will take human blood, the medicinal leech, and this is unfortunately now very rare (and not present in our sample).

Watching the leeches move in the Tupperware tub was a treat; the way they extended and contracted themselves was incredible, and their undulating swim was beautiful to behold.

We also found beetle and fly larvae, and large rafts of blueish springtails.

Using identification charts

Consulting the FSC Guide “The Freshwater name trail” I followed the instructions on how to calculate a biotic index for the habitat.  This is done by adding up a series of “scores” given to stream animals, then dividing the total by the number of animal types found.  Scores vary from 0 (no life) to 10 (clean and unpolluted stream).  Our score at Aberedw was 6.7, and so I realised this stream was a little more polluted than the one we examined in Tyclau Hill with RWT.

I’d expected to come across dragonfly and damselfly larvae

but a little research shows these are uncommon in streams (although you do get demoiselle nymphs and adults in running water).

Not only have I learnt lots from the biolblitz, and been able to re-visit past natural history illustrations of freshwater life, but I’ve also rekindled my passion for seeking out life in streams and ponds; I can’t describe how thrilled I am to be paddling about in streams with a guide-book and a magnifying glass again.  I tell you, this is the life!

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