The observations of Stegostoma fasciatum pictured here (Fig. 1; Supplementary video 1), occurred in 53 m depth, approximately 38.8 m from Dampier (20.0901S, 116.3673E), Western Australia. The sharks first entered the field of view 53 min after the stereo-BRUV had reached the sea floor and were visible for 17 sec before swimming out of view (Fig. 1A). The sharks returned 16 sec later and remained in view for a further 25 sec (Fig. 1B). Unique markings behind the pectoral fins identified that these were the same individuals as first encountered. Sex was determined by the presence or absence of claspers which was clearly visible in the footage. The male individual was biting the female’s tail for the entirety of all observations and the bite location remained unchanged between observations. The male was measured in a single length as 154.26 cm; the female could only be measured in sections and was estimated to be 151.98 cm in length. Including the two S. fasciatum reported, 218 individual fish from 25 species were recorded in this deployment. Habitat in the region is dominated by soft sediment, with complex invertebrate communities recorded intermittently. The habitat present at this stereo-BRUV deployment was diverse and included turfing algae, hydroids, sponges, and octocorals growing on a mixed substrate of sand and rocky outcrops.
We believe this is the first documented observation of pre-copulatory behaviour in free living zebra sharks. Pre-copulatory biting behaviour observed here is not unique to zebra sharks (see). Males are described biting and holding onto the fins (most commonly the pectoral and dorsal fins) and flanks of female sharks in several species. Pratt and Carrier (2001) discussed that these behaviours invoked female acquiescence and were used to facilitate insertion of the clasper and maintain proper position and proximity until copulation was complete. In contrast, we observed a male zebra shark biting the tip of the female’s caudal fin whilst not in a position to insert its clasper. Biting the caudal fin is a behaviour rarely described, but the male was likely in the early stages of courting, trying to slow and tire the female to then obtain a better position for clasper insertion. Kunze and Simmons (2004) described the same behaviour in captive zebra sharks, where biting occurred over several days. The female shark we observed did not have visible bite marks on her fins or flanks, which could suggest the pair had not been interacting for long and that courtship had just begun.
Little is known about where and when zebra sharks copulate. Seasonal aggregations have been observed in southeast Queensland, although it is difficult to know if these aggregations facilitate reproduction as no copulation events have been documented. If zebra sharks copulate in depths like that recorded here (53 m), then it is understandable that little is known about their reproductive behaviour as observations at these depths are difficult to obtain. Furthermore, if the depth and location of this observation is a typical courting area for zebra sharks then the implications for management need to be considered, particularly with trawl fisheries operating beyond the 50 m contour in the region. Stereo-BRUVs were able to capture this rarely observed behaviour which provides an integral step towards a better understanding of this endangered species’ reproductive behaviour. Furthermore, information on the size of the sharks and the depth, habitat and location of this interaction provides a scientific record useful for biologists and managers and may contribute to prompting species-specific research in this unique region.