Reef sharks: recent advances in ecological understanding to inform conservation

Abstract

Sharks are increasingly being recognized as important members of coral-reef communities, but their overall conservation status remains uncertain. Nine of the 29 reef-shark species are designated as data deficient in the IUCN Red List, and three-fourths of reef sharks had unknown population trends at the time of their assessment. Fortunately, reef-shark research is on the rise. This new body of research demonstrates reef sharks' high site restriction, fidelity and residency on coral reefs, their broad trophic roles connecting reef communities and their high population genetic structure, all information that should be useful for their management and conservation. Importantly, recent studies on the abundance and population trends of the three classic carcharhinid reef sharks (grey reef shark Carcharhinus amblyrhynchos, blacktip reef shark Carcharhinus melanopterus and whitetip reef shark Triaenodon obesus) may contribute to reassessments identifying them as more vulnerable than currently realized. Because over half of the research effort has focused on only these three reef sharks and the nurse shark Ginglymostoma cirratum in only a few locales, there remain large taxonomic and geographic gaps in reef-shark knowledge. As such, a large portion of reef-shark biodiversity remains uncharacterized despite needs for targeted research identified in their red list assessments. A research agenda for the future should integrate abundance, life history, trophic ecology, genetics, habitat use and movement studies, and expand the breadth of such research to understudied species and localities, in order to better understand the conservation requirements of these species and to motivate effective conservation solutions.

Size structuring and allometric scaling relationships in coral reef fishes

“…It also would be useful to investigate predator size–prey size relationships and ontogenetic diet shifts in a broader range of coral reef predator species to determine how general size structuring is in coral reef food webs. Sharks, for example, are important coral reef predators that were not included in this analysis, but which may play a key role in ecosystem function (Osgood & Baum ; Roff et al . ).…”

Acoustic telemetry and network analysis reveal the space use of multiple reef predators and enhance marine protected area design

“…Although the MPA should prevent finning events in the lagoon, the risk is further realized by the capture of tagged lemon sharks at Marie-Louise and Bird Island. These captures emphasize that for wider-ranging species management tools like the MPA need to be coupled with broader fisheries management strategies in order to reduce mortality of wider-ranging adults and be effective at promoting recruitment [15,47], such as catch quotas, size limits, time/area closures or even a larger shark sanctuary that covers at least the Amirantes. rspb.royalsocietypublishing.org Proc.…”

“…A combined appreciation of shark behaviour, habitat use and population structure can help frame the scale at which management efforts may be required [15]. Consequently, this study analysed detailed, long-term movements of hawksbill turtles and five shark species at a remote atoll in the Seychelles, specifically investigating whether an MPA designed for reefs and turtles would also be sufficient for the local sharks, and if not how could it be adjusted to accommodate them.…”

“…Yet such information is rarely available at the point of inception, and MPA boundaries can be established with limited information, making them less likely to succeed [18,19]. To conserve ecosystem services, MPA design should also consider multiple species [20,21], as efficacy will probably vary between species with different behaviours, life-history traits and vulnerability to fishing pressure [15].…”

“…A common tool to combat overfishing, especially in tropical ecosystems, is the designation of marine protected areas (MPAs), which can be very effective, depending on their size, level of restriction and associated enforcement [14,15]. The initial design of an MPA should be informed by the movements and habitat use of the target species, to ensure that it covers sufficient critical habitat to be effective [16,17].…”