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 involved 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 freshwater 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
multielemental 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 individual 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.