Habitat-use of the vulnerable Atlantic Nurse Shark: a review

Abstract

Human activities have led to the loss of critical habitats for aquatic species at such an accelerated rate that habitat modification is considered a leading threat to biodiversity. Sharks and rays are considered the second most threatened group of vertebrates that have also suffered from habitat loss, especially in nursery grounds and reef-associated species. In this sense, actions toward the conservation of critical grounds for species survival are urgently needed, especially for those threatened with extinction. This study aimed to gather and provide information on the worldwide distribution and habitat association of the 'vulnerable' Atlantic Nurse Shark Ginglymostoma cirratum through a literature review performed at the Dimensions research database. A total of 30 studies published between 1950 and 2021 were retained since they defined at least the type of habitat in which G. cirratum was associated. Most studies covered the Floridian ecoregion, where G. cirratum is more common and abundant. Reefs, seagrass, sandy, rocky, mangrove, and macroalgae accounted for the majority of habitat associations, with a higher diversity of habitats detected within marine protected areas (MPAs). Ginglymostoma cirratum was recorded at a maximum depth of 75 m, temperatures ranging from 25 °C to 34 °C, and salinities between 31 and 38 ppt. Neonates were associated with shallower habitats (<20 m), mostly reefs, rocks, macroalgae, sandy shores, and seagrass, in an average temperature of 26 °C and salinity of 36 ppt. Breeding events and habitats were reported by 11 studies, 72.7% of them in shallow waters, mostly inside MPAs (90.9%). Our findings highlighted the key role played by MPAs in protecting essential grounds for threatened species, such as the Atlantic Nurse Shark. Major ecoregions (e.g., the Eastern Atlantic) are still underrepresented in the scientific literature as long as studies aim specifically to assess G. cirratum habitat association. Thus, further insights into the essential habitats needed to conserve the Atlantic Nurse Shark can still emerge from future studies. Considering the recent IUCN extinction risk status change in G. cirratum (i.e., Data Deficient to 'Vulnerable'), new conservation measures that integrate habitat protection and management are urgently needed and should consider the data collected herein.

Keywords: Conservation; Ecosystem; Habitat association; Marine protected areas.

Figure 1. Number of publications per year dealing with the Atlantic Nurse Shark Ginglymostoma cirratum according to our review (see Methods for details).

Colors indicate the field of research according to the Australian and New Zealand standard research classification (ANZSRC).

Figure 2. Heat map of the number of publications dealing with the Atlantic Nurse Shark Ginglymostoma cirratum per marine ecoregions of the world (MEOW).

Figure 3. Heat map of the marine ecoregions of the world (MEOW) showing: (A) number of publications with Atlantic Nurse Shark habitat by ecoregion; (B) frequency of habitat types per Northern and Southern Atlantic provinces.

Figure 4. Frequency of the Atlantic Nurse Shark Ginglymostoma cirratum habitats within and outside marine protected areas.

Figure 5. Number of studies of Atlantic Nurse Shark habitat types by sex ratio (A) and number of occurrences of Atlantic Nurse Sharks at habitat types by life stage classes (B).