Anadromous, or even its Greek etymological meaning of “running up” (from ἀνά /aná, “up” + δρόμος /drómos, “running”), don’t really do justice to the life cycle of the sewin/sea trout/Salmo trutta.
Like salmon, these fish return to spawn in the very same waters (usually) in which their eggs had been laid, after a life at sea. They’re thus described as being anadromous. However, unlike their more famous and often larger cousins, the Atlantic salmon, Salmo salar, much less is known about the life cycle of sea trout. Although recent times have seen this knowledge expand considerably. (Thanks to the Wild Trout Trust for the summary below).
My interest in the subject was piqued by a very special moment last Saturday, just as most of the rugby following fraternity would have been settling down to watch the World Cup final at the Stade de France. Something made me tweak the drawn quilt covering our front door, and I was greeted by a fairly bright moon peeking out from stormy-looking, racing clouds. I checked the diary, and that night was indeed a full moon. Given I’d been planning to have another scout of our stream this year for possible spawning salmonids, now seemed like a good time.
Our neighbour Glyn, who was the previous owner of Gelli Uchaf before he sold it to us and moved up the hill, told us years ago of his memories of hoiking out big fish from the stream, with his own trident-style gaff which the local blacksmith had made for him. In those days the river ran thick with fish, and he’d always manage to catch one or two. I’d checked just when this was, and he said it was always around the end of October when he’d go down with his torch to spot them.
Since my own observations with spawning brook lampreys, in the same stream, and indeed then discovering the spawning habits of marine King Ragworms, not to mention more aggressive honey bee behaviour, which all seem to be linked to full moons, I reckoned just after dark on this mild, mainly cloudy night would be worth the wet walk. Togged up and torched, I thought about the camera but decided to leave it behind. By now the moon had slipped behind the clouds as I headed down the hill and began working my way upstream from the lowest section of our land.
The water conditions weren’t ideal for observation, since the level was still quite high, but at least the spate-carried silt had cleared and with the main torch beam I could vaguely make out the gravelly bottom. When I looked before, I had no real expectation of what or where I might see anything. As with any predator scanning a scene, I was carefully looking for aberrations from the constantly variable riverbed. A different form or shape? Perhaps a different colour, or movement? I had at the back of my mind any large fish might show itself with a silvery flash.
I’d worked my way past the first section of bank, and on past a wide detour round the section where storm Callum’s deluge had gouged away a big section of meadow bank. This is gradually returning to field, albeit at a lower level, as subsequent floods dump debris onto this stone-strewn area. Returning slowly and quietly to the bankside, just above the tail of a run the torch beam swung back from the far bank and instantly I picked up a large linear, dark olive form, mid-stream. As I did a mental double-take, convinced that this WAS a big fish, it flexed its form and in a couple of seconds had moved towards and upstream from me, disappearing beneath the undercut bank a few yards ahead of me, between the roots of a young Alder tree.
So at last, after all these years, a definite clear sighting of a fish of perhaps 40 to 50 cm in length. Certainly massive compared to the small fry and up to 6-inch trout which we regularly spot throughout the year, if we approach the bank edge with care. Exactly where and when I might have expected to find one. I’ve become very tired in recent times of YouTubes, or zooms, often involving investment opportunities, where the presenter tells you that they’re “really excited” by their latest development. But for me, on this wet Welsh upland stream bank, it undoubtedly was the case. My neck hairs stood. I was really excited.
The following morning I returned to the scene – needless to say no fish were visible, but I did think there was a largeish area of gravel centred around where I’d seen it, which looked remarkably clean and fresh. 
As one might expect if large fish had been creating a redd, and spawning, as in the video below, by Jack Perks.
The next question for me, though was what fish was it – a sewin or salmon? And this is where my own journey of discovery began.
We’ve often assumed the small fish we see might be young brown trout, or after Glyn’s fish-catching stories, maybe even juvenile salmon. They certainly have the classic thumb marks along their sides, though these are common to both salmon and trout parr.
However, the fact that I’d found the fish at night and that it lacked any real silver sheen made me think more of Sewin. Sewin are notoriously shy fish and tend to only move within rivers after dark. Serious anglers catch most of them, using a fly, after dark, which is an incredibly challenging thing to do. I found the following quote from an angler about catching and releasing a large sewin on the river Tywi this season, on May 7th (click on the link for photos of the fish!):
“Tonight I fished Llandeilo waters, caught a couple of little brownies early on in the evening but later heard a couple of fish entering the pool. Didn’t feel overly optimistic as the moon was rising and a clear sky. That said, I focused in areas where there was some shade from the moon. Around 11.30pm the line went tight and I struck into something solid and the line tore away as the fish raced around the pool taking me down to the backing twice and coming out of the water landing with an almighty splash! I eventually managed to get the fish into the shallows and really struggled to get it into my 20” folding Mclean net. I was nervous to keep the fish in the water,quickly got the measuring tape out but unfortunately only managed a few rather poor limited photos.
Got a good measure of the fish and it measured just over 30 inches, exactly 77cm which according to the length/weight calculation for Tywi sea trout estimates it to be 12.7lbs. It was an absolutely fantastic silver sea trout with a huge back and tail, the stuff of dreams! The main thing is the fish went back strongly (and I was left shaking on the bank!!) Fish caught on a Rob Redman Blue Widow/Tywi Special variant (25mm intruder shank) fished on a type 3 sink tip line.”
The biology of sewin (the favoured local Welsh name) or seatrout is a very interesting and complex story. They are genetically one and the same Salmo trutta, as brown trout, the native trout of many of the lakes and rivers of the UK and Ireland. However, a proportion of the fish hatching from eggs laid and developing as juvenile fry can reach a point when a combination of selection pressure, mainly from lack of available food in the stream, combined with genetic variations, triggers a fundamental behavioural and physiological change. Click here for an excellent summary of how this is thought to play out. The image from this summary, below, illustrates this simplistically.
Such small fish, still parr like in appearance, migrate down into the lower reaches of their river system and gradually adapt in the estuarine brackish water to the salinity of seawater. At this stage, they’re known as smolts, and in early spring, shoals of these now more silvery-looking small fish will head out to sea, in search of richer feeding grounds. The same journey occurs with salmon parr and smolts, except this happens with every salmon. None are left behind in the rivers to live out their lives as freshwater fish, which is what happens to a large percentage of the brown trout, Salmo trutta, siblings of the sewin.
What happens to the fish while at sea has been the subject of much research in recent years, given the declines in wild Atlantic salmon, and sea trout which occurred in the late twentieth century. Many salmon are now known to migrate huge distances to feed off the coast of Greenland/Iceland or Norway. It seems, thanks to the work of the Celtic Sea Trout project, (CST), that most sea trout stay much closer to their home rivers. The last technical report from this collaborative project covers a massive 850 pages, which I very fast skim read! But it does highlight several points.
Firstly, the Afon Tywi river catchment is both the longest of any river entirely contained within Wales, but also the most productive in terms of the numbers of sea trout of any river in Wales which enters into the Irish Sea.
As well as producing the largest mean size of seatrout
The Twyi catchment tributaries have also been assessed for water quality as below:
Once any returning spawning fish make it back through the red, poor water quality of the Tywi estuarine zone below Carmarthen, water quality begins to improve, and once fish have turned North into the Afon Cothi, the water improves to “good”. The fish would then turn left into the Afon Marlais and left again near Llansawel to arrive in “our” stream, the Afon Melinddwr (which translates as “mill water”).
The CST data suggests that many sewin stay within 60 KM of their home river estuary, feeding principally as surface pelagic feeders on a diet of sand eels, sprats, herring and occasionally mackerel, although they will take shellfish from the sea floor occasionally. After a variable number of seasons at sea, they’ll return to their home river, enter the estuary in spring, and then gradually move up the river system to reach their stream of origin by mid-autumn to spawn. As they do so, they largely cease feeding and their colour reverts to darker tones more similar to their non-migrating siblings. Given the issues they face with natural predation at sea, and within the river system from kingfishers, herons, and otters, let alone the often very polluted water they encounter, both in rivers, and the immediate coastal estuary zones where sewage discharges are now known to occur on a horrifyingly frequent basis, any fish that do make it back are true survivors, the fittest and indeed luckiest of the population.
This particular fish, if it got as far as actually spawning when I saw it, then had the disruptive force of a major deluge flowing over the redd where the eggs would have been laid, within just 24 hours. Dramatic enough to overtop the scene by some 2 feet, and rip up this section of bank, just below the run’s end.
I’ll be intrigued to look for the tiny fish next spring which emerge from their gravel base to feed for the first time around March/April, beginning another cycle of life. Unlike most salmon, the sewin adults aren’t doomed after spawning – many will return to the sea and complete the journey several times in their lifetime, adding a degree of resilience to the species’ survival chances.
Before leaving this subject, and lest anyone think mine is just another dodgy tale of vastly exaggerated size, then consider this real-life story, which took place on the same Afon Tywi on Friday 28th July 1932. Alec Allen, fishing near Nantgaredig, must have had the shock of his life when in low water conditions he hooked and landed the largest fish ever caught by rod and line on a British river – a whopping 176KG sturgeon, measuring 2.79 metres! It was foul hooked, but Lewis seized the chance as it moved into a shallow run to rush forward with his steel gaff. The fish reacted violently, bent the gaff straight and with a flick of its huge tail caught Allen and knocked him over and onto the river bank. Eventually struggling to escape in shallow water, the hapless monster was clubbed to death by Allen who’d picked up a rock from the river’s edge. The very detailed angler’s tale and backstory including a picture of this monster fish beside Allen can be found on this wonderful page. Well worth a read as an insight into the life in rural Wales at that time, and how the news hardly merited a mention in the newspapers of the day. This same river Annan website has some excellent photos of caught salmon, brown and seatrout which illustrate how seatrout colour changes as they return into their home waters, to become much darker, and the sort of olive green colour I witnessed.
Sewin 04/11/2023
Did you glimpse eternity last night?
Beneath the fast, cold millstream flow.
The Hunter’s moon above, bright white,
The aged moraine, disturbed, below.
What tales to tell, if you could speak.
Your unfamiliar siblings, soon
scattered by this freak, and terror-dumb,
might wait, and hear. Untold, you hold, mid-run.
Remember then, through genes or fate, or hunger pangs, you left.
Charged Pwll Coch’s blood-remembered scene,
Past DJ’s slate and banks, dull green
Through Sawel’s sweet vale, Marlais’s blue rush.
Down, faster, rippling Cothi rills,
Next, narrow gorge, raw power and thrills
Swept right with Tywi torrent joined, and on.
Swam Allen’s bludgeoned-sturgeon pool.
At last, you linger, hesitate –
that brackish taste, that sewered-impure.
Lone migrant’s choice – to leave? Too late.
Soon shoaling smolts mass, reassure.
Thence out to sea, the space, the sprats
The sand eel spree, the seals, scale scars.
Then some time, underneath wide stars,
A memory. Of that eternal glimpse.
You turn, and now earth magnets show,
Tastes beyond Llansteffan’s murky flow.
Spend summer, still, day-hunkered, low.
Autumnal spates test sea-sprung bow
Four arrowed turns lead home. Below cloud
scudded moon (if this is home), you wait.
And dream of a reprise (while dyfrgi
hunts, grabs, tastes your distant mate).
The next dull morn. This stream runs clear.
No sun, no stars, no moon to steer.
And are you spent? Or gone? Or here?
Will you return, this time, next year?
Reflecting on the amazing story of migration that sewin undertake, a song from the eighties came to mind, from a CD we own of that era – “The Friends of Mr.Cairo” a collaborative album between Jon Anderson and Vangelis. It was released twice, in quick succession in 1981. The first edition had poor sales, so this track was added as the opener to the second edition and went on to become a hit single in its own right.
….But if my spirit is strong,I know it can’t be longNo questions I’m not aloneSomehow I’ll find my way home…
__
Despite some pretty shocking weather over the last 2 weeks, with well over 200 mm of rain falling onto already saturated ground, we’ve had enough warmth and sunshine to enjoy fabulous autumn colour in many of the trees around the garden, as well as a stunning display from our Saxifrage fortunei in the copse, which I thought merited another What3Plants short video, so here it is:
Our first snowdrop flower, a form of Galanthus reginae-olgae, opened around October 20th, which just as with the spawning sewin, reminds us that as one season and year is winding down, another is about to begin. Always a poor doer here, it really craves more light and less rain, I suspect. Still, it’s just about hanging on in this relocated position, at the base of the fabulous Sorbus sargentiana which has to rank as our favourite and most spectacular autumn colour tree, and features in many of the following photos, viewed over several days, and from different angles.
I’ll finish with a selection of recent rainbows and this leaf colour splendour, and these words from Siegfried Sassoon’s poem (thanks to Rowena for introducing me to this powerful verse):
Gloria Mundi
Who needs words in autumn woods
When colour concludes decay?
There old stories are told in glories
For winds to scatter away.
Wisdom narrows where downland barrows
Image the world’s endeavour.
There time’s tales are as light that fails
On faces fading forever.
