Fishing the Sea-Trout: Sewin
Sea-trout, sewin, white trout, and migratory trout are synonyms for the form of trout (Salmo trutta) that travels between sea and river for the purposes of feeding and breeding. When we recall that the freshwater brown trout is considered a very sporting fish it will be appreciated that in the sea-going form the qualities of vigour, speed, and stamina are developed to a superlative degree.
All sorts of theories have been advanced to explain why a race of trout should find it beneficial to migrate, none of them wholly satisfactory. One explanation put forward is that since food is short in acid rivers the trout go to sea in order to feed. This theory, however, fails to explain why sea-trout are found in rivers of rich feeding such as the Hampshire Avon and the Dorset Frome.
The name ‘sea-trout’ covers a multitude of sea-going, coastal, and estuarial trout forms, but the sea-trout of popular parlance may be described loosely as a trout with the proportions and wandering habits of a salmon, which indeed it closely resembles. The most scientific way of distinguishing salmon from sea-trout is by a scale count: the former have 10-12 scales from lateral line to dorsal fin, the latter 16.
Sea-trout are restricted almost entirely to our western seaboard, although they are caught in nets along the beaches of north Norfolk. They seldom enter rivers there, however. One netted at Blakeney recently carried a Scottish Dee tag. A few rivers as far east as Dorset contain them. Elsewhere they make occasional appearances but clearly find conditions not quite to their liking. Their presence in one or two Sussex rivers suggests that abstraction and pollution have driven the sea-trout from the east coast rather than the operation of any natural factor.
Broadly speaking, the sea-trout is a fish of the summer. Some rivers do have spring runs — in the Towy, for example, fresh sea-trout are caught as early as April — but a useful run of fish seldom occurs much before late May. These early summer fish are the best of the season, being clean, in perfect condition, and of substantial weight. The weights range from about 1.5 kg (3 lb) to 3.2 kg (7 lb) with a sprinkling of specimens as big as 5-7.5 kg (12-17 lb).
Sea-trout smolts migrate during May and weigh, on average, about 75 g (3 oz). In July, August, and September they run upriver again, having quadrupled their body-weight in the sea. Indeed, many now weigh over 450 g (1 lb). These young returning sea-trout are known as whiffing.
From June onwards sea-trout run up the rivers freely. They are fond of hot, fine weather and anti-cyclones, and dislike muggy weather with depressive electrical clouds. I find that they run best when the weather is fine and the springs are in full flow. Much information can be derived from a study of the springs that feed the river. Springs are fed from underground reservoirs, and once these become exhausted the rivers rapidly fall to drought level and sea-trout stop running.
In the biggest rivers the ideal time for a sea-trouting holiday is probably the middle fortnight in June. Given hot sun, cool breezes, and a reasonable flow of water, the best sea-trout of the season will be found filling the lies. Fishing in July and August is often disappointing. September is often good, although the average size of the fish is reduced owing to the large numbers of whitling in the rivers.
As with salmon, there are early and late rivers, so it pays to make careful inquiry before booking advance accommodation on a strange stream. Small rivers may contain sea-trout from August onwards, and broadly speaking the smaller the river the later it is likely to be, but there is no hard-and-fast rule; some quite small waters have a June run.
The sea-trout first put in an appearance, of course, in the lower reaches and in bigger rivers it may be some weeks before they penetrate to the middle and upper water. This point is important to the angler who finds himself fishing water eighty or so kilometres from the sea. He may find it pays him to drive about forty kilometres downstream.