The silvery sea trout is simply the migratory variant of the brownie you catch in your local lake. But, in keeping with its vast marine environment, it grows into a far larger fish Until recent times it was thought that the sea trout, Salmo trutta as it was originally classified, was an in-dependent species, while brown trout were known as Salmo fario. Scientific opinion now is that they are both of the species Salmo trutta. Even as long ago as 1887 it was asserted that there existed only this latter species of trout in Britain. This uncomplicated classification may satisfy those with a scientific turn of mind, but it does nothing for the angler who finds vast behavioural and environmental differences between the sea trout and the non-migratory ‘brownie’. What, then, is a sea trout? Sadly, a satisfactory answer is not forth-coming and we must accept that the sea trout, for want of factual infor-mation, is nothing more than a migratory brown trout. Just what induced the initial migration is little more than pure speculation; but there is on record the scientific opi-nion that all the family Salmo were of marine origin and that it was the last Ice Age which caused some to be landlocked and others to develop the migratory instinct, perhaps as long ago as 100,000 years.
As with the salmon, therefore, the sea trout’s origins are not fully understood. It follows a very similar life pattern to that of the salmon, and there was a time when our sea trout were simply called salmon-trout. Obviously, all the Salmo species had similar beginnings and for this reason many angling novices have difficulty distinguishing one from the other. There are differences, however, some subtle, others appreciable.
Sea trout’s spawning time
Sea trout usually begin their spawning in October. On average, they are two or three weeks earlier than salmon, but there is no hard and fast rule. November is probably the month of greatest activity but some fish, according to one authority, may spawn throughout the winter. He adds that, although ripe (ready to spawn) sea trout, which have not begun to shed ova or milt, may be seen in January, and very occa-sionally in February, their spawning season is generally shorter than that of the salmon, and much shorter than that of the non-migratory brown trout.
Sea trout prefer smaller gravel than salmon for the construction of the redd in which the eggs are laid and fertilized, and, like salmon, find sand and mud unsuitable. Some will spawn in water barely deep enough to cover their backs, and they may be found in many small Scottish Highland burns with access to the larger river systems.
Smolts in the tideway
As with the salmon, it is the female sea trout which, with broad sweeps of its tail, makes the redd. Females are said to be able to produce 700-800 eggs for each pound of weight, but this is only a very rough guide. Like salmon, and depending on water temperature, a period of 90-120 days elapses before the eggs hatch. Much the same behavioural and growth pattern as in young salmon then occurs , but once the young sea trout smolts hit the tideway they tend to tarry, moving backwards and forwards on every ebb and flow for a much longer period than their salmon counterparts.
After feeding and growing for 2-5 months, some of the smolts which descended in spring to the sea return in summer or autumn to the river. Here they are known by different names—finnock (and variants), whitling, herling, sewin, sprod, peal, among others—according to locality.
Why these small fish spend autumn and winter in their rivers of birth is not known. It is known that only few perform the reproductive act and that most come and go as the whim seizes them, either in-dividually or in shoals; but that the longer they stay in freshwater the more their appearance and condition deteriorate. Many anglers seek them for sport and the table during early spring in the River Spey, for instance, which can be simply heaving with finnock up to the end of April. This seems to be the time when they make for the sea once more.
The anatomical differences bet-ween salmon and sea trout, although subtle, soon become evident. There is, of course, the undisputed scale count from the lateral line to the shoulder, but the tail is the main guide, and usually produces instant recognition. In salmon the tail is slightly forked and even when stret-ched still shows a concave shape. In sea trout the wrist of the tail is different and the tail itself is almost square or convex. All salmon may be picked up by the tail, but if an unidentified fish slides out of the hand it is a fair bet that it is a sea trout. To the trained eye there are several other identifying factors, but for the novice the tail is probably the best guide.
The run upriver
Following a return of the young fish to the sea, many classic rivers will experience the first runs of mature sea trout. On the Spey, for instance, it is quite normal to find fresh sea trout as early as April. But the main runs may still not come until May and June and it frequently happens that the bigger sea trout run the river earlier in the season. Not all these fish will be destined to spawn the following winter.
There is little doubt that most sea trout endeavour to spend some part of their year in freshwater. They are much more nomadic in their migra- tions than salmon. Indeed, only a very small percentage of salmon will ever make more than one freshwater migration. Many die as kelts and of those that do reach the sea again quickly, some fall to marine predators. Sea trout, however, have been known to migrate into freshwater as many as ten times, although there are few facts available on the number of times successful spawning may take place.
Mature sea trout weigh from 1lb to over 20lb but today it is quite an event to catch one over the 10lb mark. Scandinavia has produced some of the largest sea trout cap-tured, while the Dyfi in Wales has yielded at least two specimens of over 20lb. Until March 1969, the British rod-caught record was a fish of 22Jib caught by S R Dwight in 1946, coming from the River Frome in Dorset. Now, the record is open and can be claimed by anyone making an authenticated catch of a 15lb fish or larger.
Like salmon, the returning sea trout does not need to take food in freshwater, but, unlike salmon, does occasionally take food and seems to have a digestive mechanism adquate for this. But since sea trout do not seem to increase in length in freshwater, despite some feeding, they might be expected to suffer less from their stay there than salmon. The species, however, even maiden sea trout, do deteriorate after leaving the sea; and in many districts ripe fish at spawning lose as much weight for length as salmon.
Stored tissue and fat There is little doubt, therefore, that the entire process of staying in freshwater calls upon the sea trout to use up much of its stored tissue and fat. Whatever food it might occasionally take, it certainly does not get sufficient to sustain it. Sea trout which have run the river in April or May can be quite sorry-looking creatures by the end of September, and all sporting anglers will return such fish to the water with as little injury as possible.
On some rivers, of course, the sea trout do not begin to run until July or August. This can be a time when low water might frustrate easy passage up the river. In this respect sea trout are much more tenacious than salmon, and may frequently be seen moving through water barely sufficient to cover their backs.
Like salmon, the sea trout must have water of high purity. Sadly, suitable environments are continually being eroded and there are only a handful of worthwhile rivers in England today. Wales is better, but we look to Scotland for the majority of good rivers. Although more esteemed for its salmon fishing, the Spey is possibly the most prolific sea trout river in the United Kingdom. The Tweed gets good runs of big sea trout which few people ever seem to catch. The small rivers of the west coast and the Isles abound with sea trout, but they are fickle and shy fish.
Superior to the salmon?
As a sporting fish, they are highly prized by anglers, many of whom are of the opinion that good sea trout are not only more sporting than salmon, but superior on the table. Unless the water is high and slightly coloured, the fish can be very difficult to catch in daylight. Night fishing with a fly is the epitome of sport, and on the classic streams it is the most practised method.
The sea trout, therefore, does not yet have to face the pressures now being made on salmon resources. With modest amounts of good husbandry, it seems to be a fish which can take reasonable care of itself, but it must never be seen casually as an indestructible resource. Unless something is done quickly about the erosion of the suitable environment, the sea trout may well pass into history as one of the greatest, but extinct, fishes.