-Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life-history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life-history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3-5 sea-winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life-history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life-history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world-wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in 1 Un resumen en espan˜ol se incluye detra´s del texto principal de este artı´culo. Introduction''There is no group or family of fishes that supplies better materials for the study of the effects of geographic or physiologic isolation, or which presents more curious and interesting facts in their life histories than do the various species of Salmonidae.'' (Evermann 1925) The salmonid subfamily Salmoninae comprises about 30 species ...

Projected shifts in climate forcing variables such as temperature and precipitation are of great relevance to arctic freshwater ecosystems and biota. These will result in many direct and indirect effects upon the ecosystems and fish present therein. Shifts projected for fish populations will range from positive to negative in overall effect, differ among species and also among populations within species depending upon their biology and tolerances, and will be integrated by the fish within their local aquascapes. This results in a wide range of future possibilities for arctic freshwater and diadromous fishes. Owing to a dearth of basic knowledge regarding fish biology and habitat interactions in the north, complicated by scaling issues and uncertainty in future climate projections, only qualitative scenarios can be developed in most cases. This limits preparedness to meet challenges of climate change in the Arctic with respect to fish and fisheries.

The effects of formalin and ethanol preservation on the d 13 C and d 15 N isotope signatures of Arctic charr Salvelinus alpinus muscle tissue were examined. The lipid content of the tissue samples studied ranged from 3Á6 to 6Á1% and was not correlated with the magnitude of observed isotopic shifts in preserved samples. Ethanol and formalin significantly depleted and enriched, respectively, the d 13 C isotope signatures of preserved tissues when compared to control samples. Ethanol did not significantly enrich d 15 N signatures in comparison to controls, whereas formalin did. A meta-analysis of multiple species effects further demonstrated significant preservation effects in fish tissue. Statistical analysis of data obtained by correcting preserved tissue isotope signatures with literature, bootstrapped or meta-analysis derived correction factors demonstrated significant differences between corrected and control sample isotope signatures or failure to produce a unity slope when the data sets were regressed against one another. Species-specific, bootstrapped linear correction models resulted in no such errors. Results suggest that speciesspecific correction methods should be used for fishes because of the known wide variation in fish tissue lipid content and composition. Accordingly, the use of pilot studies will be required to develop correction factors that properly adjust for preservation effects when interpreting temporal patterns in historic analyses of food webs.

Arctic freshwater and diadromous fish species will respond to the various effects of climate change in many ways. For wide-ranging species, many of which are key components of northern aquatic ecosystems and fisheries, there is a large range of possible responses due to inter- and intra-specific variation, differences in the effects of climate drivers within ACIA regions, and differences in drivers among regions. All this diversity, coupled with limited understanding of fish responses to climate parameters generally, permits enumeration only of a range of possible responses which are developed here for selected important fishes. Accordingly, in-depth examination is required of possible effects within species within ACIA regions, as well as comparative studies across regions. Two particularly important species (Arctic char and Atlantic salmon) are examined as case studies to provide background for such studies.

Field-collected otolith samples of young-of the-year Arctic charr (Salvelinus alpinus) and brook charr (Salvelinus fontinalis) and monitored water temperatures were used to estimate a delta(18)O fractionation equation for the genus Salvelinus. When compared to literature reported equations, the developed fractionation equation had a statistically similar slope but dissimilar intercept. Statistical similarities among fractionation equation slope estimates suggest a common otolith delta(18)O incorporation response among fish species that may be interpreted as widespread equilibrium otolith delta(18)O deposition. Statistical dissimilarities among intercept estimates question broad applicability of any single fractionation equation to all fish species and were interpreted here to have biological meaning as a result of known differences in standard metabolic rates among species. Attempts to statistically cross-validate fractionation equations by prediction of water temperatures used in other fractionation studies indicated significant biases in the range of -7.9 to 6.7 degrees C that preclude the broad use of any single fractionation equation for accurate thermal reconstructions. Differences in equation intercepts and the prevalence of predictive biases do not support the conclusion of previous studies concerning the wide applicability and/or general accuracy of fractionation equations and suggest fractionation equations are best developed at the species- or taxon-specific (e.g., genus) level.

Eleven Arctic charr (Salvelinus alpinus) (370-512 mm) and eight sea trout (Salmo trutta) (370-585 mm in length) were tagged externally or internally with depthand temperature-measuring data-storage tags (DST) before they were released into the sea in the Alta Fjord in north Norway in June 2002. All sea trout were recaptured after they spent 1-40 days at sea, while all Arctic charr were recaptured after 0.5-33 days at sea. On average, trout preferred water about 0.6 m deeper and 1.3°C warmer than Arctic charr. Arctic charr spent >50% of their time between 0 and 1 m depth, while trout spent >50% of their time between 1 and 2 m depth. Both species spent >90% of their time in water no deeper than 3 m from the water surface. However, sea trout dove more frequently and to greater depths (max. 28 m) than Arctic charr (max. 16 m), and these deep dives were most frequently performed at the end of the sea migration. Arctic charr demonstrated a diel diving pattern, staying on average about 0.5 m deeper between 08:00 hours and about 15:00 hours than during the rest of the 24 h, even though there was continuous daylight during the experiments. When comparing data obtained from the DSTs with temperature measurements within the fjord system, the two species were observed to select different feeding areas during their sea migration, the sea trout choosing the inner and warmer parts of the fjord, in contrast to the Arctic charr that preferred the outer, colder parts of the fjord. The observed differences in migration behaviour between the two species are discussed in relation to species preferences for prey and habitat selection, and their optimal temperatures for growth.

Stomach content analyses were conducted on Atlantic salmon Salmo salar post-smolt (average size, 119-154 mm fork length, L F ) caught in eight large Norwegian fjord systems along a north-south geographical axis during 1998-2001. In general, post-smolts from southern Norway showed low feeding intensity in the fjords, whereas extensive feeding was observed in fjords in the northern and middle parts of Norway. The marine diet mainly included different crustaceans and in particular marine pelagic fish larvae (sand-eels Ammodytes spp., herring Clupea harengus and gadoids), but with a substantial spatial and annual variation in prey diversity and feeding intensity. Insects were most frequently taken in the estuary, although fishes often made a large contribution in mass. In contrast, fishes, and to some extent various crustaceans (particularly Hyperiidae, Gammaridae, Euphausiacea and Copepoda) dominated the diet in the middle and outer parts of the fjords, where post-smolts also fed more extensively than in the inner part. The results indicate that extensive feeding immediately after sea entrance may be more common for post-smolts in the northern and middle parts of Norway, than in the southern fjords. The observed differences in post-smolt feeding may be due to spatial and temporal differences in prey availability within and between the different types of fjord systems, and this might influence post-smolt growth and survival. # 2004 The Fisheries Society of the British Isles

Restriction fragment length polymorphism analysis of mitochondrial DNA (mtDNA) was used to reconstruct postglacial dispersal routes of arctic charr Salvelinus alpinus in North America. Twelve of 35 restriction enzymes detected polymorphisms among representative populations, revealing two distinct lineages with an estimated nucleotide divergence of 1.32%. Subsequent screening of 869 fish from 54 populations with four diagnostic restriction enzymes showed that these lineages have largely allopahic distributions, suggesting their dispersal from separate northern and eastern glacial refugia. In addition, geographical and genetic structure among eastern populations suggested the existence of a second eastern refuge. Among the three lineages, the most divergent (Arctic) lineage occurred from Alaska east to northern Labrador. Quebec, New Brunswick, and New England were colonized by a second (Laurentian) lineage, and Labrador by a third group. Contact between refugial groups was only detected in two Labrador populations. The Arctic lineage was highly differentiated from eastern North American and European haplotypes, and probably diverged during the early Pleistocene. By contrast, the Laurentian and Labrador groups were similar to Old World charr, suggesting a shared ancestry during the mid-Pleistocene. In addition, the close relationship between Labrador and Laurentian charr indicates their probable divergence during the Wisconsinan glaciation.Australia. rivers in Greenland and Arctic Canada, S. alpinus probably persisted through repeated glaciations despite drastic habitat and range alterations (Johnson 1980;Crossman & McAllister 1986). The timing of postglacial processes and events (retreating ice margins, freshwater runoff, eustatic changes in sea level, and isostatic rebound) were probably pivotal in determining the species' postglacial dispersal, as arctic charr require stable freshwater habitats for overwintering (Johnson 1980). As well as providing freshwater habitats for over-wintering populations, glacial meltwater would have facilitated marine dispersal by lowering salinity, thus enhancing survivorship of anadromous colonists (Dempson 1993). Arctic charr probably followed the retreating glacial margins closely, as distributional patterns of fish species in areas with substantial isostatic rebound indicate that arctic charr colonized deglaciated habitats before other fish species (Power et al. 1973;Hammar 1987). 0 1% Blackwell Science Ltd Qadri SU (1974) Taxonomic status of the Salvelinus alpinus complex. J o u m l of the Fisheries Research Board of Canada, 31, 13551361.Reist JD (1989) Genetic structuring of allopatric populations and sympatric life history types of charr, Salvelinus alpinus/malma,