Widespread diversity deficits of coral reef sharks and rays

Abstract

A global survey of coral reefs reveals that overfishing is driving resident shark species toward extinction, causing diversity deficits in reef elasmobranch (shark and ray) assemblages. Our species-level analysis revealed global declines of 60 to 73% for five common resident reef shark species and that individual shark species were not detected at 34 to 47% of surveyed reefs. As reefs become more shark-depleted, rays begin to dominate assemblages. Shark-dominated assemblages persist in wealthy nations with strong governance and in highly protected areas, whereas poverty, weak governance, and a lack of shark management are associated with depauperate assemblages mainly composed of rays. Without action to address these diversity deficits, loss of ecological function and ecosystem services will increasingly affect human communities.

Long term declines in the functional diversity of sharks in the coastal oceans of eastern Australia

“…We report a significant decline in the functional diversity of targeted apex sharks in eastern Australia, as illustrated by reductions in overall trait space and therefore overall ecological functioning. These changes likely reflect the combined impacts of both large scale regional and international harvesting pressure on large and highly mobile fish populations 8 , 12 . Many of the species that have declined in abundance in eastern Australia are large sharks with large home ranges (10 s to 100 s of kilometres and sometimes larger) 15 , 32 that are also threatened globally by overharvesting in commercial, recreational and artisanal fisheries 8 , 16 .…”

“…Sharks are functionally important components of coastal and oceanic food webs as they can exert top-down pressure on food webs at large spatial scales through the direct and indirect effects of predation 10 , 11 . They are also well researched, meaning that their abundance and diversity is well understood in many settings 8 , 12 . However, they are experiencing significant threats and declining due to human activities (e.g., overharvesting, climate change, habitat loss) 8 , 12 – 16 , with overfishing alone driving one third of shark and ray species to extinction 17 .…”

“…They are also well researched, meaning that their abundance and diversity is well understood in many settings 8 , 12 . However, they are experiencing significant threats and declining due to human activities (e.g., overharvesting, climate change, habitat loss) 8 , 12 – 16 , with overfishing alone driving one third of shark and ray species to extinction 17 . The removal of high order species such as sharks from marine food webs is amplified when the functional traits of these species are also lost from the community.…”

Offspring size resolves a latitudinal population growth rate paradox in rays and skates

“…Recent experimental evidence from caged and uncaged epifaunal communities suggests predation rates are greater in shallow, tropical waters than at higher latitudes [61]. Additionally, evidence from Baited Remote Underwater Video (BRUVs) surveys along a gradient of fishing pressure, reveals that the decline of sharks leads to increases in ray abundance, consistent with predation driving community structure on tropical coral reefs [62,63].…”

Seasonal distribution patterns and conservation gaps of blue sharks in the Indo‐Western Pacific Ocean

“…The waters surrounding Australia have many MPAs, and a significant amount of blue shark occurrences were located in this region. This suggests if these MPAs and sanctuaries were managed effectively in terms of excluding high bycatch fishing activities (currently not; Devillers et al, 2020), they might serve as important refuges for blue sharks, as for some reef sharks (Simpfendorfer et al, 2023). In contrast, we identified shark-fishery hotspots in the warm season in the subtropic northwest Pacific, where there is a lack of large MPAs or sanctuaries.…”