Sea Trout Stocks Research Articles

Genetics of brown trout(Salmo truttaL.) stocks above and below impassable falls in the Conwy river system, North Wales

Samples of trout (Salmo trutta L.) were taken from four rivers in the Conwy system, North Wales: the Roe and the Nant-y-goron, which support sea trout stocks, and the Iwrch and Machno which are situated above impassable waterfalls and contain resident trout. Tissue samples from the fish were used in electrophoretic analysis of enzymes. Fourteen loci were scored of which six were polymorphic (Pgi-2, Gpd-2, Ldh-5, Mdh-2, Mdh-4 and Ck-2). Allele frequency data from these loci were used to test interpopulation heterogeneity, which indicated that the two upstream samples were probably reproductively isolated from each other and also from the downstream samples. Mean heterozygosity was generally lower in the upstream stocks compared with the sea trout populations. UPGMA cluster analysis based on Nei's genetic distance (D) revealed a clear dichotomy between those stocks above, and those below waterfalls. This was best explained by the presence of two strains of trout in the system. One strain, the resident trout occurring above impassable waterfalls, was characterized by high frequencies of the Ldh-5(100) allele, the other strain, principally consisting of sea trout, exhibited high frequencies of the Lhd-5(90) allele.

Migratory salmonids of the Estuary and Firth of Clyde

SynopsisThe paper describes the salmon and sea trout stocks of the rivers entering the sea via the Estuary and Firth of the Clyde including the Rivers Clyde, Leven, the Carts, the rivers of the Ayrshire coast and those entering via the sea lochs and from the Mull of Kintyre. Particular attention is paid to the recent return of salmonids to the Rivers Clyde and Cart, which have been denied to migratory species for over a century because of pollution in the upper Clyde Estuary. The changing environmental conditions, which have made the reappearance of migratory salmonids possible, are described and the future importance of the fishery assessed.

A Survey of Population Characteristics for Red Drum and Spotted Seatrout in Louisiana

Red drum and spatted seatrout stocks were sampled from seven separate study areas along the Louisiana coast and from one estuarine area in Texas, with additional intensive temporal (monthly) and microgeographic (range of salinity regimes) samplings being carried out in one Louisiana study area. Condition coefficients, which did not appear to be affected by salinity regimes within the microgeographic sampling area, varied significantly according to study area, with Texas fish showing significantly lower condition coefficients than Louisiana fish. Van Bertalanffy growth equations were fitted and annual mortality rates were estimated to obtain preliminary estimates of yields, population numbers, and densities of these species in Louisiana.

The fishes of inland waters in the Outer Hebrides

SynopsisOnly euryhaline fishes were able to recolonize Outer Hebridean fresh waters after the last glaciation so that inland waters now contain only six indigenous, truly freshwater species; salmon, trout, charr, three- and ten-spined stickleback and the freshwater eel. Parts of some lochs are invaded by the sea at stages in the tidal cycle and some 20 species of marine fish may be found at times in inland waters.Both salmon and sea trout occur in all the larger freshwater systems and sea trout are also found in many of the minor ones.The original sea trout gave rise to sedentary brown trout populations similar to those of the mainland.Fluctuations in the Hebridean salmon catch suggest that the stock is affected by the same factors as those affecting Scottish west coast stocks generally: the vast-majority return to fresh water as grilse, while sea trout stocks have been declining over the last 25 years.Brown trout and eels are almost ubiquitous. Charr occur in Lewis and parts of North Uist but have not been reported from Harris or South Uist and are now only present as sedentary forms. The three-spined stickleback is more widely distributed than the ten-spined.Outer Hebridean lochs in general have special scientific value because, unlike many Scottish mainland lochs, they have not been affected by the introduction of alien species and some are still in an unexploited state.