Dataset: Antarctic toothfish otolith reference set age data from the Ross Sea, Antarctica

Three trained readers aged each otolith (n = 185) two times for each method in random order and blinded to previous estimates. Otoliths were aged according to criteria established by Underkoffler et al. (2010): beginning at the nucleus, readers first counted annuli along the dorsal-distal axis of the transverse section until the axis growth zones became compressed, then readers moved their count path to the proximal side of the otolith section where zones were more visible (SC-CAMLR 2001; Brooks et al. 2011). For the direct view method, readers independently estimated age using a Lecia MZ95 stereomicroscope with transmitted light at 10x—60 × magnifications. For the image view, three images of each otolith (whole, dorsal and ventral views) were captured using a Lecia S9i microscope camera with transmitted light at 20x – 55 × magnifications using LAS X Life Science Microscope Software and saved as TIFF files (2160 × 1080-pixel resolution). Readers independently estimated ages using the images on 4 k-resolution monitors.