Extracting a century of preserved molecular and population demographic data from archived otoliths in the endangered European eel (Anguilla anguilla L.)

Archived otolith collections represent an invaluable source of information to study demographic and genetic changes in commercially important fish populations. Studies combining both approaches are however rare and reliable extraction of molecular and population demographic data from the same collection of otoliths has never been assessed in the endangered European eel (Anguilla anguilla L.). Here we evaluate various DNA extraction protocols to compare DNA yield, microsatellite amplification success, genotype integrity and precision of age determination for eel otoliths that have been archived for 4 weeks, and for 28 and 48 years. Our results show a high amplification success and an equal genotype integrity for DNA fragments extracted from both recently sampled otoliths and high quality reference DNA tissue. Although historical samples yielded low amounts of DNA, PCR amplification was successful and genotyping reliable for short fragments, but decreased significantly with PCR fragment size. None of the extraction protocols caused physical damage to the otoliths and precision of age determination was high for both treated and untreated otoliths. Hence, the methodology can be applied as a standard for the further joint analysis of past demographic and genetic changes during the last century in the highly exploited European eel and in other fish requiring urgent conservation measures.status: publishe