Quantifying fish otolith mineralogy for trace-element chemistry studies.

Area of Science:

• Ichthyology
• Geochemistry
• Materials Science

Background:

• Otoliths are crucial for understanding fish ecology and environmental history.
• Trace-element analysis in otoliths is a common method for ecological inference.
• Otolith mineralogy, specifically calcium carbonate polymorphs (aragonite, calcite, vaterite), can influence trace-element incorporation.

Purpose of the Study:

• To quantitatively assess the mineralogical composition of Chinook salmon otolith pairs.
• To determine if mineralogical differences exist between left and right otoliths within a pair.
• To evaluate the accuracy of visual inspection for identifying otolith polymorphs.

Main Methods:

• Neutron diffraction was employed to identify and quantify mineral phases.
• Raman spectroscopy was utilized for mineralogical analysis.
• Otolith pairs from Chinook salmon (Oncorhynchus tshawytscha) were analyzed.

Main Results:

• Mineralogical compositions frequently varied between left and right otoliths in a pair.
• Accurate identification of calcium carbonate polymorphs was rarely achievable through visual inspection alone.
• The study highlights potential heterogeneity in otolith mineralogy within individual fish.

Conclusions:

• Otolith mineralogical composition can differ significantly between paired otoliths.
• Visual inspection is insufficient for accurate polymorph identification.
• Future research must investigate otolith compositions and their impact on trace-element data and environmental interpretations.