A New Research Tool for Use in Sharks and Rays: Relevance of Reproductive Hormone Levels in the Skin of Small-Spotted Catshark (

The present study marks a significant step forward in validating the use of skin biopsies for measuring reproductive steroid hormones in sharks. Given the conservation concerns surrounding many chondrichthyan species and the growing emphasis on adhering to the 3R principles in wildlife research, we should prioritize the acquisition of data through non-destructive or minimally invasive sampling techniques collected remotely. Dart skin biopsy samples can be collected remotely, without the need to chase, capture, and restrain the animal. Accordingly, the present study aimed to (i) develop a suitable extraction and analytical technique for reproductive hormone determination in shark skin biopsies and (ii) evaluate whether sex steroid hormones detected in shark skin differ between males and females and depending on males' maturity. The results of assay validation demonstrated that the commercial enzyme immunoassay used can provide reliable measures of progesterone, 17β-estradiol, and testosterone measured in shark skin extracts. After ensuring that reproductive hormones are accurately measured in this sample type, we compared hormone levels between males (mature and immature) and females to evaluate the variation in reproductive hormones relative to sex and males' maturity stage. We detected significant differences in skin hormone levels between sexes, suggesting that this technique may be a promising alternative approach for obtaining relevant biological data in free-ranging sharks. By employing this novel technique, we expect to gain a deeper understanding of the reproductive processes of living chondrichthyans, which is essential for formulating effective science-based conservation and management strategies.