Remote reefs and seamounts are the last refuges for marine predators across the Indo-Pacific

Abstract

Since the 1950s, industrial fisheries have expanded globally, as fishing vessels are required to travel further afield for fishing opportunities. Technological advancements and fishery subsidies have granted ever-increasing access to populations of sharks, tunas, billfishes, and other predators. Wilderness refuges, defined here as areas beyond the detectable range of human influence, are therefore increasingly rare. In order to achieve marine resources sustainability, large no-take marine protected areas (MPAs) with pelagic components are being implemented. However, such conservation efforts require knowledge of the critical habitats for predators, both across shallow reefs and the deeper ocean. Here, we fill this gap in knowledge across the Indo-Pacific by using 1,041 midwater baited videos to survey sharks and other pelagic predators such as rainbow runner ( Elagatis bipinnulata ), mahi-mahi ( Coryphaena hippurus) , and black marlin ( Istiompax indica) . We modeled three key predator community attributes: vertebrate species richness, mean maximum body size, and shark abundance as a function of geomorphology, environmental conditions, and human pressures. All attributes were primarily driven by geomorphology (35%−62% variance explained) and environmental conditions (14%−49%). While human pressures had no influence on species richness, both body size and shark abundance responded strongly to distance to human markets (12%−20%). Refuges were identified at more than 1,250 km from human markets for body size and for shark abundance. These refuges were identified as remote and shallow seabed features, such as seamounts, submerged banks, and reefs. Worryingly, hotpots of large individuals and of shark abundance are presently under-represented within no-take MPAs that aim to effectively protect marine predators, such as the British Indian Ocean Territory. Population recovery of predators is unlikely to occur without strategic placement and effective enforcement of large no-take MPAs in both coastal and remote locations.

Social–ecological feedbacks drive spatial exploitation in a northern freshwater fishery: A halo of depletion

“…These results are strikingly similar to predictions from foraging theory whereby spatial exploitation can lead to a halo of depleted prey patches near consumer origins (Ashmole, ; Storer, ). Reduced body sizes and fishing quality of local fisheries are also consistent with empirical observations (Cinner et al, ; Kaufman, Snucins, Gunn, & Selinger, ; Keppeler et al, ; Letessier et al, ; Post et al, ) and predictions from spatial exploitation models, like Carpenter and Brock () and Matsumura et al (), that show expanding–contracting effort patterns most affects local fisheries. The combination of anglers' imperfect knowledge, hyperstable catches and low willingness to substitute travel times for improvements in other site characteristics may deplete fisheries nearest large sources of gravity as anglers are unwilling (or unable) to track biotic changes in resource quality (Johnston et al, ; Matsumura et al, ; Post et al, ).…”

“…The halo contracts once local fisheries recover, or distant patches are depleted. Such processes are associated with fishery collapses globally (Cinner et al, ; Keppeler et al, ; Letessier et al, ; Post et al, ).…”

Strengthening the synergies among global biodiversity targets to reconcile conservation and socio‐economic demands

“…These areas include large and remote portions around Rocas Atoll, Fernando de Noronha, and Trindade and Martin Vaz, where there are many vulnerable species and relatively fewer threats (Halpern et al, ; Pinheiro et al, ). Emerging evidence shows that reefs with low levels of human disturbance can support high functional diversity and biomass of fishes, representing refuges for sharks and other predators (D'agata et al, ; Juhel et al, ; Letessier et al, ). The implementation of proactive, large‐scale initiatives such as the establishment of large no‐take MPAs could safeguard these remaining near‐pristine marine areas, benefiting even highly mobile marine species (Graham & McClanahan, ; Juhel et al, ; Speed et al, ; White et al, ).…”

Submerged Carbonate Banks Aggregate Pelagic Megafauna in Offshore Tropical Australia

“…This dearth of information hampers ecological monitoring efforts at local and regional scales, and undermines appropriate evaluations of management performance within the recently established national network of Australian Marine Parks (AMPs) 2 . Novel approaches to data collection and analysis are thus critical to addressing existing knowledge gaps and determining the degree to which pelagic communities are represented within offshore AMPs around Australia and beyond (Letessier et al, 2019).…”

“…BRUVS are now a prominent element of Australia's strategy for standardized ocean monitoring (Bouchet et al, 2018;Przeslawski et al, 2019), and offer a robust, costeffective, and non-invasive approach to sampling that overcomes the traditional shortcomings of diver-reliant surveys (Langlois et al, 2010;Murphy and Jenkins, 2010). Extensively used in studies of benthic assemblages inside and outside protected areas (Mallet and Pelletier, 2014), they have recently been engineered for mid-water applications (Santana-Garcon et al, 2014a;Letessier et al, 2019), making them a suitable choice for surveying the neritic (10-250 m) depths of the Oceanic Shoals AMP. Our objectives were to: (1) document the pelagic wildlife inhabiting the western part of the park, (2) estimate total species richness in the area, and (3) quantify spatial variation in community composition, species richness, and relative abundance, in relation to seafloor geomorphology.…”