Comparison of the performance of scale and otolith microchemistry as fisheries research tools in a small upland catchment

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis of recently formed Salmo trutta scale hydroxyapatite and otolith aragonite provided biogeochemical tags of S. trutta at six sites (>7.5 km apart) in a small upland catchment (drainage area: ~1800 km²). 87% and 89% of fish were correctly classified to their site of capture based on Sr, Mn, Ba, and Mg concentrations in scales and otoliths, respectively. Sr, Mn, and Ba were highly significantly correlated between structures of the same fish (P < 0.001). Ba and Mn in both structures were significantly correlated with stream water chemistries at each site (P < 0.05). Significant differences among sites were found in 11 element concentrations in scales and six element concentrations in otoliths (P < 0.05). Broadening the suite of elements improved the classification to 90% when using otoliths and 92% when using scales. Although there appears to be some degree of postdepositional change in scale hydroxyapatite in sea-run S. trutta, it was not sufficient to completely overprint the freshwater signature. Scales offer a nonlethal sampling alternative to otoliths and appear to provide a biogeochemical tag comparable in performance, but further work needs to examine the degree of postdepositional change in scale hydroxyapatite.