A variety of biological tracing projects are being undertaken using radiogenic isotopes as tracers of migration habits. This work relies on the uptake of Sr and Pb into organisms. The isotopic composition of these elements reflects that of their habitat/ nutrient source. If physiological elements are selected such as otoliths (fish earbones) and teeth, that grow in increments over time, then a time-resolved record of the migratory habits of the animal can be constrained. This approach can be extended to other organisms such as corals, to monitor temporal changes in water chemistry at particular sites.
We are collaborating with Dr Peter Outridge of the Geological Survey of Canada, investigating the migratory habits of Arctic walrus populations using the Pb isotopic composition of their teeth, determined by laser-ablation PIMMS. This is the only possible means of constraining migratory habits over timescales of 10's of years.
An additional project involves members of Biological Sciences at Durham and is focussed on using Sr isotopes in otoliths to trace the breeding and migratory behaviour of fresh water and ocean-dwelling fish. This data is also obtained using laser ablation PIMMS. The figure below shows scans from the centre to the edge of otoliths from two different fish. The Korean species is a fresh-water species. The radiogenic nature of the Sr in the otolith reflects soluble Sr in rivers eroding ancient bedrock (probably the Sino-Korean craton). The North Sea species has an average Sr isotopic composition that is equivalent to modern seawater and indicates that this species has spent its life in the open sea. The method has the obvious potential to trace the migration of fish such as salmon, from the ocean, into freshwater, to breed. We are interested in pursuing other collaborative studies using these techniques.