Resources Allocation Among Arctic Char in Closed Arctic Lakes: Implications for Population Structure and Regulation

In closed arctic lakes, we observe a strong cycle in population structure in Arctic char (Salvelinus alpinus) while population abundance remains generally stable.  We hypothesized this cycle was driven by strong internal density dependence that could operate via: 1) food limitation including cannibalism, and/or 2) size-based niche differentiation.  We tested these hypotheses using a long time series of population data, diet analyses, and isotope –based trophic position and overlap in two different arctic lakes, AK.   We observed no evidence of cannibalism; however, other work has shown that cannibalism can be extremely influential even at very low levels (< 5%), yet extremely difficult to detect.  Furthermore, large and small adult char exhibited spatial niche differentiation; large char (> 300 mm) switched to a more littoral foraging pattern, incorporating a large proportion of snails in their diet relative to pelagic small adults.  The number of ice-free days appeared to be extremely influential in determining recruitment success; however, increased productivity resulting from lake fertilization stabilized the population structure at high densities of small char.  A better understanding of the processes regulating these populations will be critical in predicting the effects of climate change and in contributing to synthetic evaluations across arctic ecosystems.