Exploring Structural Environmental Enrichment and Welfare in Captive-Bred Nursehound Sharks (Scyliorhinus stellaris)

Sharks play a pivotal role in maintaining the ecological balance of the seas; however, the general loss of biodiversity is particularly affecting this group. Restocking strategies are far less common for elasmobranchs than for teleosts, but in the Balearic Islands, a conservation program aims to breed nursehound sharks (Scyliorhinus stellaris) in captivity for subsequent release into the sea, as a conservation measure for these endangered populations. Improving welfare during captive rearing may be important for the success of such programs, yet basic information on the husbandry of this species is lacking. In this exploratory study, we evaluated the effects of two types of structural environmental enrichment (EE), seaweed (SW) and tiles (TL), compared with a non-enriched control, on the growth, body condition, and space use of 45 captive-bred juveniles over six months. Growth did not differ significantly among treatments, although SW individuals showed consistently higher mean length and weight, and enriched animals maintained a better body condition than controls over time. The SW group expanded its core area of use earlier than the other groups, whereas TL individuals progressively aggregated around the tiles. When both structures were offered, naïve control animals mainly selected the seaweed, whereas tile use was only observed in animals previously exposed to them. To our knowledge, these are the first published data on growth, space use, structure selection, and sedation with buffered MS-222 for captive-bred nursehounds. Although these results should be interpreted with caution owing to the use of a single tank per treatment, they provide a baseline for future research on the welfare and rearing of this species in captivity.