Rostral tooth microwear and ultrastructure of the barbels and rostrum tip in the Common Sawshark Pristiophorus cirratus and their proposed behavioural implications

Although sawsharks are frequent by-catch in commercial deep-water fisheries, our understanding of their behaviour is limited; in particular with regards to how they use their barbels and rostrum. This project employed a variety of techniques to infer how sawsharks use their barbels and rostrum. Evidence from histology and preliminary fluorescent microscopy work suggests that the barbels serve a tactile function, since they lack sensory structures such as taste buds, free neuromasts and ampullae, and contain neurons in the epidermis that may be connected to tactile receptors or free nerve endings. Regression analysis also provided evidence to suggest that sawsharks may have a preference as to whether they use the left or right barbel to sense the environment (behavioural lateralisation). Microwear (i.e. scratches) on the rostral teeth of sawsharks and sawfishes was found to be similar, suggesting that both elasmobranchs use their rostrum for a similar purpose. Analysis of stomach contents from recently caught sawsharks showed that diet consisted of small fish and prawns; however, whole prey items did not show signs of impalement by rostral teeth. Histological investigation of the unusual structure on the tip of the rostrum (named the "fingerprint") regarding a possible sensory purpose was inconclusive. These results provide important first steps in understanding the biology and behaviour of sawsharks and may prove useful for the management of threatened sawshark species, as well as deep-water fisheries in general.