Stocking of non-native Salmoninae into North American waters began around 1870. Brown trout (Salmo trutta) from Europe established populations across North America and is the only successful inter-continental introduction. Introductions of native salmonids within North America but outside their native ranges have been common. Ecological effects of salmonid introductions. include competition, predation on native salmonids and other fishes, environmental modification through digging of redds in stream bottom substrates during spawning, and introduction of parasites and disease to native fish. Direct genetic effects from stocked salmonids are caused by interbreeding with native species. Indirect genetic effects may result through selective forces and/or a reduction of effective population size, genetic drift, and inbreeding. Management actions used to remove non-native salmonid populations include chemical reclamation and construction of barriers to movement. Salmonid stocking as a management practice is appropriate for species or population rehabilitation. Continued stocking of non-native salmonids should cease where viable native salmonid populations exist. New introductions of Eurasian species should not be made because effects are unpredictable. Aquaculture and the creation of transgenic fish pose special threats to North American salmonids. The era of widespread, intentional introductions of salmonids by man justifiably is drawing to a close.

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Abstn:ct. Macroinvertebrate annual production was estimated in three Minnesota streams that differed m watershed geologic origin and in total alkalinity. Annual mean alkalinities (as CaCO) in the Caribou Riv~r, Blackho?fRiver, ~~d No~h Branch Creek were 34, 83, and 245 mg/L, respecti:ely.Annual ~ro~uctwn ~y h~rb1vore-detnt1vore_ mvertebrates was lowest in the Caribou River (wet mass: 27.~ g/m ): mtermedmte m the Blackhoof River (36.9 g/m 2 ), and highest in North Branch Creek (I 19.6 !¥m ). Est~mates _of annual production by invertebrate carnivores followed the same pattern: lowest m the Canbou River (5.5 g/m 2 , intermediate in the Blackhoof River (6.5 g/m 2 ), and highest in North Bran~~ Cre~k (12.8 g/m 2 ). These estimates of annual production were positively associated with alkahmty, mtrates, and fish standing stocks.

Little is known about the phenotypic diversity of lake trout Salvelinus namaycush in large North American lakes outside the Laurentian Great Lakes. This study tested the hypothesis that phenotypic diversity in Great Slave Lake, Northwest Territories, Canada, is associated with water depth, as was observed during similar studies of lake trout in Lake Superior. We describe the association of body size with color, buoyancy, and morphology; compare these phenotypic traits among depth strata; and establish whether lake trout phenotypes occur as discrete groups. Phenotypic diversity increased among fish longer than 43 cm standard length. In water less than 50 m deep, large lake trout (!43 cm) were light in color, buoyantly heavy, and streamlined and possessed short pectoral fins. In water deeper than 50 m, large lake trout were dark in color, buoyantly light, and deep bodied (less streamlined) and had long pectoral fins. Without assigning descriptions to individuals before the analysis, we identified two phenotypic groups. These groups represented nondiscrete phenotypes; lake trout of intermediate shape had intermediate fin lengths, capture depths, and buoyancies. The phenotypic patterns observed in Great Slave Lake were similar to the lean and siscowet forms that currently exist in Lake Superior. Deepwater forms, previously believed to be endemic to the Great Lakes, are more geographically widespread and may represent diversity typical of this species in large, deep lakes. We suggest that the lake trout phenotype associated with deep water (buoyantly light, long pectoral fins) is adaptive for daily vertical migrations.

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Teleost fishes are prominent vertebrate models of evolution, illustrated among old‐world radiations by the Cichlidae of East African Great Lakes and new‐world radiations by the circumpolar Arctic charr Salvelinus alpinus. Herein, we describe variation in lake charr S. namaycush morphology, life history, physiology and ecology, as another example of radiation. The lake charr is restricted to northern North America, where it originated from glacial refugia and diversified in large lakes. Shallow and deepwater morphs arose in multiple lakes, with a large‐bodied shallow‐water ‘lean’ morph in shallow inshore depths, a small‐bodied mid‐water ‘humper’ morph on offshore shoals or banks, a robust, large‐bodied moderate to deep‐water ‘redfin’; morph and a large‐bodied deep‐water ‘siscowet’ morph at depths > 100 m. Eye position, gape size, and gillraker length and spacing adapted for feeding on different‐sized prey, with piscivorous morphs (leans, siscowets and presumably redfins) reaching larger asymptotic size than invertivorous morphs (humpers). Lean morphs are light in colour, whereas deepwater morphs are drab and dark, although the pattern is reversed in dark tannic lakes. Morphs shift from benthic to pelagic feeding at a length of 400–490 mm. Phenotypic differences in locomotion, buoyancy and lipid metabolism evolved into different mechanisms for buoyancy regulation, with lean morphs relying on hydrodynamic lift and siscowet morphs relying on hydrostatic lift. We suggest that the Salvelinus genus, rather than the species S. alpinus, is a diverse genus that should be the subject of comparative studies of processes causing divergence and adaptation among member species that may lead to a more complete evolutionary conceptual model.

Resource polymorphisms are widely observed in fishes; however, ontogenetic contributions to morphological and ecological differences are poorly understood. This study examined whether ontogenetic changes in niche partitioning could explain morphological and buoyancy differences between lake trout ( Salvelinus namaycush ) morphotypes in Great Slave Lake (Northwest Territories, Canada). Morphometric analysis, buoyancy, capture depth, diet, and stable isotope data were used in concert to determine whether (i) differences occur in small, as well as large, lake trout, (ii) ontogenetic changes in morphology and buoyancy correlate with shifts in depth or diet, and (iii) a subset of small trout, putatively identified as “humpers”, are distinct from other morphotypes. Ontogenetic changes in lake trout morphology were associated with an ecological shift between benthic and pelagic feeding. Resource partitioning between lean and siscowet-like trout occurred within benthic (small trout) and pelagic (large trout) habitats. The humper subset did not differ from small siscowet-like trout. By combining multiple methods and an ontogenetic perspective, our study provides novel perspectives on resource polymorphisms in large, deep lakes and on existing interpretations of stable isotope data from large lakes in general.

Fish migration in large freshwater lacustrine systems such as the Laurentian Great Lakes is not well understood. The walleye (Sander vitreus) is an economically and ecologically important native fish species throughout the Great Lakes. In Lake Huron walleye has recently undergone a population expansion as a result of recovery of the primary stock, stemming from changing food web dynamics. During 2011 and 2012, we used acoustic telemetry to document the timing and spatial scale of walleye migration in Lake Huron and Saginaw Bay. Spawning walleye (n = 199) collected from a tributary of Saginaw Bay were implanted with acoustic tags and their migrations were documented using acoustic receivers (n = 140) deployed throughout U.S. nearshore waters of Lake Huron. Three migration pathways were described using multistate mark-recapture models. Models were evaluated using the Akaike Information Criterion. Fish sex did not influence migratory behavior but did affect migration rate and walleye were detected on all acoustic receiver lines. Most (95%) tagged fish migrated downstream from the riverine tagging and release location to Saginaw Bay, and 37% of these fish emigrated from Saginaw Bay into Lake Huron. Remarkably, 8% of walleye that emigrated from Saginaw Bay were detected at the acoustic receiver line located farthest from the release location more than 350 km away. Most (64%) walleye returned to the Saginaw River in 2012, presumably for spawning. Our findings reveal that fish from this stock use virtually the entirety of U.S. nearshore waters of Lake Huron.