Otolith chemistry to determine movements of diadromous and freshwater fish

Abstract

Determining the timing or frequency of movement of fish and the relative importance of different habitats is difficult. Advances in otolith chemical techniques and interpretations (including elemental ratios and stable isotopes) suggest that this is a powerful method for determining movement of fish. To date, the majority of applications have in- volved marine fish, however, otolith chemistry has the potential to determine movements of diadromous and freshwater fish; I therefore review freshwater applications of otolith chemistry in this paper. Despite some limitations regarding strontium:calcium (Sr:Ca) ratios (e.g. Sr concentration of the water is not always measured, Sr:Ca ratios in freshwa- ter can exceed marine waters, and mixed results for the relationship between otolith Sr and salinity), they have been widely used for a variety of applications involving diadromous species and more recently freshwater fish. In addition, barium:calcium (Ba:Ca) ratios have recently been used to determine movements of diadromous and estuarine species, as ambient ratios are possibly linked to environmental flows. Several studies have also investigated the use of multiele- mental otolith composition to discriminate between groups of fish collected from different lake or river systems, but a wider range of applications are possible. Several applications of Sr isotopes have also been investigated, most of which is focused on salmonids (e.g. distinguishing fish from different river systems, determining movement history of indi- vidual fish). Relatively few studies have investigated the use of other isotopes (e.g. oxygen, sulphur) for determining movements. Otolith elemental ratios and stable isotopes have great potential to determine movements of freshwater species, with possible applications likely to increase as analytical technology improves.