Since the mid-19th century, numerous attempts have been made to restore or enhance populations of the Atlantic salmon, Salmo salar, within the endemic range, and to establish the species in other parts of the world. Despite all efforts, salmon have become naturalized locally only in eastern North America, Argentina, the Faeroe Islands, and New Zealand. Principal factors affecting the disappearance, restoration, or naturalization of populations are water temperature and availability of suitable spawning and nursery sites. Commercial exploitation of the species in coastal and offshore waters is viewed internationally as a factor of increased importance in the numerical regulation of river spawning runs. A further expansion of the world distribution of Atlantic salmon by naturalization seems unlikely except in areas where preliminary plantings have been made or brood stocks are presently held. Atlantic salmon produced by commercial sea farming operations in Norway, Scotland, Spain, and France are considered to be of comparable quality to fish harvested from the wild. Also, there is presently interest in the potential of sea ranching of Atlantic salmon. Key words: zoogeography, endemic range, naturalized range, artificial propagation, environmental impact, exploitation, aquaculture
Lake trout, Salvelinus namaycush, released into Tadenac Lake as juveniles, show a pronounced acceleration in growth rate, following a change in diet from benthic invertebrates to rainbow smelt, Osmerus mordax, beginning at age 6 (> 30 cm). An abrupt increase in the rate of mercury accumulation in white muscle of these fish occurs at the same time. Mercury levels in lake trout ([Formula: see text] = 0.24–3.44 μg/g) and coresident smelt ([Formula: see text] = 0.06–0.48 μg/g) from Tadenac and eight neighboring lakes reveal maximum levels reaching 10.0 and 0.84 μg/g, respectively. Mercury levels in lake trout from Tadenac Lake, an undisturbed PreCambrian Shield ecosystem without detected indigenous sources, exceed the "safe" level (0.5 μg/g) at sexual maturity and at a size less than generally acceptable for human utilization. Mercury accumulation by the trout is correlated with length (r = 0.92) in each lake population examined, but substantial among-lake differences occur in fish of comparable ages. As the growth rates are similar in various waters, differences in extent of mercury accumulation is attributed to differences in mercury availability among lakes. In view of a strong correlation (r = 0.96) between mercury levels in smelt and trout calculated at standardized length, it is proposed that the smelt is an appropriate indicator species for the ranking of cold-water lakes relative to the availability of mercury for uptake by lake trout and other living aquatic organisms.Key words: mercury uptake, lake trout, rainbow smelt, growth rate, diet
This note supplements the original paper by MacCrimmon and Marshall (J. Fish. Res. Bd. Canada 25: 2527–2548, 1968) in presenting modified and more complete information on the native range, attempted introductions, and present world distribution of the brown trout.
Juvenile Atlantic salmon (Salmo salar) meristic and morphometric characteristics were examined from 47 European and North American river populations. The relative importance of continental origin, stream gradient, overall temperature regime, and seasonal temperatures in explaining the phenotypic variation of these populations was evaluated using multi‐way ANOVA. Ecological factors explained a greater percentage of the variance than continental origin for both meristic and morphometric characters. Stream gradient was the most important factor explaining morphometric variation and April‐May mean temperature was the most important factor explaining meristic variation.
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