habitat use of Arctic char (Salvelinus alpinus) in a small Arctic lake, monitored by acoustic telemetry.Abstract -Acoustic technologies were applied to describe how landlocked Arctic char from Iqalugaajuruluit Lake, Baffin Island, interact with its lacustrine habitat. Acoustic data from the lake bottom was collected using sonar equipment and substrate types were verified with benthic grabs and mapped in a geographic information system. Arctic char movements during the open water period were recorded from char fitted with acoustic tags. The distribution of the tagged Arctic char in Iqalugaajuruluit Lake was dependent on fish size and related to abiotic factors such as depth, substrate type and depth ⁄ temperature, temporally. The volume of water with temperatures below 6°C during the open water period may be a limiting factor for large char (>400 mm) in small Arctic lakes. The large piscivorous char are found most often in the deepest water over soft substrates and the smaller char which feed on varying proportions of invertebrates and fish were found most often over the more complex substrates such as boulders, pebbles and gravel.

Large unit cell calculations of the properties of charged point defects in insulators largely neglect dielectric polarization of the crystal, because the periodically repeated cells are so small. Embedded quantum cluster calculations with shell-model crystals, representing a single defect in a large crystal, are able to represent the polarization more realistically. For such embedded quantum clusters, we evaluate the optical excitation energy for the nitrogen vacancy in charge state (+3): v 3+ N in AlN. This is done with and without dielectric polarization of the embedding crystal. A discrepancy of a few per cent is found, when both ground and excited state orbitals are well-localized within the vacancy. We show that the discrepancy rises rapidly as the excited state becomes more diffuse. We conclude that an embedded cluster approach will be required for transitions that involve even somewhat diffuse states. The investigation is based on a new model for AlN that shows promise for quantitative accuracy.

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