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Sympatric diversification in Lake Trout is generally linked to differences in habitat use (especially depth) as a result of foraging on different prey items. However, extensive sympatric divergence has taken place in the shallow waters (≤30 m) of Great Bear Lake, with multiple Lake Trout morphs varying in head and fin characteristics. To investigate diet partitioning as a potential explanatory mechanism for this diversification, we assessed trophic characteristics and relationships among four sympatric shallow-water morphs of Lake Trout via analyses of fatty acids and stomach contents. Fatty acids and stomach contents both identified Lake Trout, Cisco and Mysis as key prey items in Lake Trout diets. Interestingly, terrestrial invertebrates were also seasonally important among morphs, reflecting temporal variability of available prey in this arctic lake. Some diet partitioning was observed among morphs; Morph 1 was characterised as a generalist, Morph 3 was more benthic-oriented, and Morphs 2 and 4 were mainly pelagic feeders. Of the latter, Morph 4 was the most specialised, whereas Morph 2 exhibited alternative feeding tactics of benthic cannibalistic and pelagic piscivorous feeding. Our findings demonstrate that complementary dietary methods can elucidate habits of opportunistic feeders, a task that can often be problematic, given their complex and variable diets. Our results add new information and perspectives on the current model of Lake Trout differentiation, demonstrating niche partitioning based on benthic versus pelagic habitat use and generalist versus specialist feeding tactics. [ABSTRACT FROM AUTHOR]

Winter aeration is often used to prevent fish winter-kill among lakes supporting recreational fisheries and is often used in conjunction with trout stocking as trout are sensitive to hypoxia. We collected limnological data as well as pelagic microcrustacea and rotifers one year before and one year after aeration was initiated in Birch Lake, located in the boreal foothills ecozone of Alberta, Canada. Using a Before-After-Control-Impact design, we compared changes in Birch Lake to those in two nearby and similarly mesotrophic, stocked control lakes (one aerated for more than six years, one unaerated). During winter, surface aeration increased the depth of well-mixed water in Birch Lake, maintaining levels of dissolved oxygen suitable for supporting stocked trout. Linear mixed model analyses indicated that among May–August water quality parameters, only phosphorus concentrations showed a marginally significant treatment × year interaction, increasing only in the unaerated control lake. Aeration did not affect the spring–summer abundance, biomass, or sizes of Birch Lake's zooplankton community. Once aerated, the microcrustacean community in Birch Lake showed partial overlap with the community in the aerated control, although this could not be statistically linked to changes in specific taxa. Ours is the first study to investigate impacts of winter surface aeration on zooplankton communities despite the numerous lakes managed under this strategy. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Great Bear Lake is the most northerly lake of its size and provides unique opportunities for intraspecific diversification. Despite increasing attention to intraspecific polymorphism, several knowledge gaps remain (e.g. determining the extent of intraspecific diversification in large relatively pristine lakes and at which spatial scale it can occur). We focused on geographical patterns of morphological differentiation within lake trout ( Salvelinus namaycush) to describe two levels of intralake diversification in Great Bear Lake. We used a combination of geometric and traditional linear measurements to quantify differences in body shape, head shape, and fin and body lengths among 910 adult lake trout from the five distinct arms of Great Bear Lake. Although head and fin linear measurements discriminated the three common morphotypes at the whole-lake level, inter-arm variation in body shape was observed within each morphotype. A comparison of genetic and morphological distance matrices revealed the lack of an association between the two sets of data, although both comparisons revealed an association in the inter-arm variation patterns among morphotypes, suggesting a phenotypically plastic response to distinct environments. The whole-lake and inter-arm morphological variation observed within lake trout demonstrates the importance of considering scale, especially across large lakes that exhibit marked complexity and a variety of freshwater habitats. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 114, 109-125. [ABSTRACT FROM AUTHOR]

Self-thinning theory predicts that decline in density with increasing individual mass should match the exponent of the metabolism-body mass relationship (∼0.9 in salmonids). However, self-thinning assumes energy equivalence (constant energy available to a cohort as it ages), which may be unrealistic for mobile taxa. I evaluate this assumption using a bioenergetic-stream habitat model to assess the sensitivity of available energy and self-thinning slopes to changes in habitat structure (percent pool). Self-thinning slopes across three age-classes of juvenile trout (young of the year, 1+, and 2+) were sensitive to both modelled habitat structure and density-independent mortality rates. Density-independent overwinter mortality generated self-thinning curves similar to those expected from metabolic allometry, even without habitat limitation (density-dependent mortality). Energy available to sympatric cohorts was unequal under most habitat configurations because of size-based differences in swimming performance that affected habitat availability and interference competition (dominance) that allowed resource monopolization by older cohorts. The optimal habitat structure that maximized abundance of the 2+ age-class (and best approximated energy equivalence) was ∼40% pool, but this value was sensitive to density-independent mortality rate and assumptions about the effect of the pool to riffle ratio on invertebrate prey production. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)