Update of age and growth validation of skates in the Ross Sea region using mark recapture

In the 2019/20 and 2020/21 fishing years, Antarctic starry skates (Amblyraja georgiana) were tagged with the antibiotic terramycin (oxytetracycline hydrochloride, OTC) or strontium chloride (SrCl₂) for a mark-recapture programme established to estimate population size and validate caudal thorn ageing techniques. Of the 4900 tagged skates, more than 2400 skates were injected (49%). Since the 2019/20 fishing season, a total of 104 skates were recaptured and retained: 103 A. georgiana and one McCain’s skate (Bathyraja maccaini, misrecorded as A. georgiana). Based on observer records, 27 recaptured skates were chemically marked, 18 with OTC and nine with SrCl₂ (26% of returned samples analysed). Possible detection of fluorescence was identified in four OTC-injected skates. At least one skate showed florescence restricted to a distinctive growth band on the caudal thorn, with an apparent small amount of caudal thorn growth beyond the uptake of the florescent band. Skates injected with strontium chloride have not been assessed yet. Given their relatively slow growth, further sampling is required over succeeding fishing years to confidently confirm age validation with caudal thorns. We recommend continued sampling of recaptured skates to maximise sampling efforts. Future analysis of SrCl₂-marked recaptured skates will be carried out to determine the usefulness of this chemical for mark-recapture.