Investigating the effect of marine reserves on coastal sharks in southern New Zealand

With the rapid increase in the use of marine protected areas, there is a need to better understand the value they offer top predators. However, in Aotearoa (New Zealand), no research has previously investigated the effects of marine reserves (i.e. Type 1 Marine Protected Areas) on such species. Research on marine reserves in New Zealand has generally focused on commercially important species, such as blue cod (Parapercis colias), snapper (Pagrus auratus), and spiny lobster (Jasus edwardsii). Considering there are 44 marine reserves of varying characteristics that overlap with the distribution of several coastal shark species, New Zealand presents an ideal location to research the effects of marine reserves on top predators. This study used a non-invasive methodology to investigate the effect of six marine reserves on the distribution of coastal shark species. Baited remote underwater video (BRUV) systems were deployed in 317 sites over two distinct regions: 192 sites in Ata Whenua (Fiordland) from July 2018 to December 2019, and 125 sites in Whaka ā Te Wera (Paterson Inlet), Rakiura (Stewart Island), from February 2018 to November 2019. A generalized linear modelling (GLM) approach was used to assess the effect of the marine reserves on two trophic levels of sharks in Fiordland. Firstly, GLM was used to assess the effect of protection on the combined relative abundance of the most common mesopredatory sharks detected. These species included the spiny dogfish (Squalus acanthias), school shark (Galeorhinus galeus), and carpet shark (Cephaloscyllium isabellum). A significant effect of the marine reserves was evident for mesopredators, suggesting marine reserves have led to an increase in their abundance or a change in distribution. Secondly, GLM was used to assess the effect of protection on the presence of broadnose sevengill sharks (Notorynchus cepedianus) and by contrast, there was no significant effect detected. For the Stewart Island data, a species distribution modelling approach was used to assess the fine scale effects of the Te Wharawhara (Ulva Island) Marine Reserve on the relative abundance of sevengill sharks. Again, no significant effect was evident. Given the marine reserves sampled are relatively small (< 40 km2), they appear to provide minimal conservation benefits for the large and mobile sevengill shark. In comparison, mesopredatory sharks with smaller home ranges may be completely protected in marine reserves, possibly allowing their populations to increase. These findings suggest that to be effective for shark conservation, marine reserves need to be appropriately sized for the ranging behaviour of the species intended to be protected. This study is the first of its kind to assess the effect of marine reserves on coastal sharks in New Zealand, and the first attempt to quantify the distribution of sevengill sharks, as well as other coastal shark species, in Fiordland