ABSTRACT: Otolith microchemistry: a proxy for short-term environmental change in lakes.

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Abstract

Otoliths, the hard calcareous (typically aragonite) structures located in the inner ear of teleost (bony) fish, are used to determine age, life history events, and environmental conditions of fish and fish populations. Strontium is a common substituent for calcium in otolith aragonite and is used to establish migratory behavior of fish. Zinc has also been reported in otoliths and may be linked to proximity to mine tailings or used as a proxy for fish size. In this work we have examined otoliths taken from fish in the vicinity of rare element pegmatites in eastern Manitoba, Canada using LA-ICP-MS. A suite of elements were detected in the otoliths as follows: Li (~3 – 95 ppm), Na (~460 – 8800 ppm), Rb (~0.2 – 80 ppm), Sr (~90 – 1500 ppm), and Cs (~0.1 – 25 ppm). Levels of element concentration varied, sometimes in correspondence to the annular structure of the otoliths, suggesting there is some periodicity to their incorporation. Preliminary results indicate that the incorporation of Li and Cs is dependant on proximity to the rare element pegmatites in that otoliths from fish captured near, or downstream from the pegmatite contain these elements, whereas fish from lakes distant to, or upstream from the pegmatite do not have these elements in their otoliths. This suggests that otolith trace element composition contains a history of the chemistry of the dissolved load in the water, which in turn can be related to the geology of the surrounding watershed. Also apparent from this data set is that different species from the same lake incorporate different amounts of the same elements. The pelagic, plankton- and insect-eating cisco contain higher concentrations of these trace elements than the bottom-feeding white suckers that principally feed on invertebrates and fish eggs. This suggests that the incorporation of trace elements into otoliths may be partially dependent on diet. This is the first reported detection of Cs and Rb in otoliths and the highest reported abundance of Li. The proximity to rare-element pegmatites of similar chemistry strongly suggests there is a link between the fish’s geographic environment and the microchemistry of its otoliths. Such information may be used to characterize and monitor lacustrine environments over a period of time.

Bibliography of Canadian Geomorphology