The effect of overwintering site temperature on energy allocation and life history characteristics of anadromous female Dolly Varden char (Salvelinus malma), from northwestern Canada

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Sandstrom, Stephen J.
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Overwintering sites used by Dolly Varden char (Salvelinus malma)(Walbaum) populations on the Yukon and Northwest Territories north slope are situated near thermal freshwater springs. These springs vary with respect to physicochemical characteristics (e.g., orifice water temperatures) which presumably place different environmentally driven energetic demands upon the fish. This study examined the possible effect of water temperature differences on energy allocation to competing life history demands of growth, reproduction and metabolism for adult female char from the Babbage and Big Fish Rivers (orifice water temperature is 4oC and 16oC respectively). Specifically, the study examined whether higher overwintering site water temperature increase the overwintering metabolic demands of adult female char, thereby compromising growth and/or reproductive effort. Results indicated that prior to overwintering, post-spawned females from the two systems had similar muscle lipid reserves, whereas gut lipid reserves were only slightly higher in females from the Big Fish River. This similarity in somatic energy reserves suggests that, despite the physicochemical differences in the springs, adult char of both systems overwinter in similar thermal regimes. This may be due to the formation of ice tunnels within the aufeis field unique to the Big Fish River. Energy allocated to growth in length was not significantly different between stocks, however, Big Fish River females had significantly greater adjusted mean dressed weights (muscle mass) than Babbage River females. Big Fish River femaleS allocated more energy to reproduction (gonad weight), when controlling for length but not when controlling for dressed weight. Additional muscle mass in Big Fish River females may permit production of larger gonads either by providing greater somatic energy supply available for gonad production and/or by creating larger body cavities for gonads to occupy... The higher water temperature (measured at the orifice) in the Big Fish River system does not appear to increase the metabolic demand of overwintering adult fish; consequently, growth and/or reproductive effort of females in this population are not constrained. However, the higher overwintering site temperature appears to lower the current reproductive potential of female char by requiring them to produce larger, and therefore fewer eggs.