Annual surface water temperature cycles of temperate zone lakes can be adequately described by a symmetrical sine wave of distinct amplitude and duration. The relationships between these sine wave components and climatic and morphometric variables were analyzed for 87 lakes spread over most of North America, and for 25 lakes located in south-central Ontario, Canada. Multiple regression equations are reported which permit estimation of the maximum annual surface water temperature (amplitude: AP) and the number of ice-free days (duration: DR) for a specific lake from data on long-term mean annual air temperature (TEMP), mean depth [Formula: see text], and fetch (FT). These estimates can be used to calculate mean surface water temperature for just the ice-free period or for an entire year.
Fish production and yields from natural lakes are related to morphoedaphic factors and regional differences in climate. To quantify the relationships on a global scale, climatic data and estimates of fish yield, total dissolved solids, and mean depth were compiled for natural lakes located between 62°N and 15°S latitude. Stepwise regression analyses showed that for intensively fished lakes (N = 43), the climatic index “mean annual air temperature” accounts for 74% of the variability of maximum sustainable yield (MSY). The morphoedaphic index (MEI), expressed as total dissolved solids divided by mean depth, accounts for an additional 7–9% of the MSY variability. This contrasts with regional studies in which the MEI usually accounts for a greater percentage of yield variability than do climatic variables. Equations presented in this study can be used to predict approximate potential yields from lakes that are currently experiencing little or no fishing pressure.
Four species of freshwater green algae spanning a size range of 0.83–325.22 pg carbon per cell were grown in laboratory batch cultures under four levels of incident irradiance. There was an inverse relationship between cell size and specific growth rate at the highest light intensity tested. As light intensity was decreased, the relationship weakened. These laboratory results, in addition to some field data from arctic lakes in Canada, support recent model predictions concerning size-dependent algal growth.Key words: algae, cell size, growth, irradiance, models, nutrients
Fishes inhabiting subarctic and temperate zone lakes exhibit distinct optimal growth temperatures and temperature preferenda. However, within regional data sets, attempts to correlate fish yields with temperature variables have generally been unsuccessful. In our study, curvilinear relationships between "long-term mean annual air temperature" (TEMP) and sustained yields of three species were fitted using data from 23 intensively fished lakes in Canada and the northern United States. Optimum TEMP values for sustained yield were approximately −1.0, 1.5, and 2 °C, respectively, for lake whitefish (Coregonus clupeaformis), northern pike (Esox lucius), and walleye (Stizostedion vitreum vitreum). These differences suggest that the influence of temperature on sustained fish yields from subarctic and temperate zone lakes may, in the past, have been underestimated.
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