Feasibility of lead-radium dating the otoliths of blackfin icefish (Chaenocephalus aceratus) and ocellated icefish (Chionodraco rastrospinosus)

Application of lead-radium dating was attempted as a feasibility study for otoliths of blackfin icefish (Chaenocephalus aceratus) and ocellated icefish (Chionodraco rastrospinosus). Because otoliths from these fishes were small and the number of otoliths available low, a whole otolith application was necessary as a first look at lead-radium levels. The application was successful as a first step in determining the parameters of future applications that would lead to a validation of age. In the current study, sample mass for the pooled otolith samples was low (~0.4 g). This finding, coupled with low radium-226 levels, led to age determinations that had a high margin of uncertainty; however, the findings led to an educated recommendation for future lead-radium dating studies for these species. Based on the measured lead-radium levels, the future direction may include further exploration of the whole otolith approach. This approach has some disadvantages, such as the circularity associated with developing a mass-growth model, but would provide the opportunity to make an age determination that does not reply on growth zone counting. Furthermore, a follow-up lead-radium dating study using cored otoliths (extraction of the first few years of growth) is possible for these species, provided there is enough sample mass and perhaps an application of micromilling. This approach would require ~150 otoliths per sample, given an arbitrary target core weight of 0.01 g, near the low end of the range used in this study. It is recommended that the collection of otoliths from these species be given a priority whenever possible to facilitate future age and growth studies and potential applications of lead-radium dating.