Abstract
Quantifying the drivers of population size in reef sharks is critical for the development of appropriate conservation strategies. In north-west Australia, shark populations inhabit coral reefs that border growing centres of human population, industry, and tourism. However, we lack baseline data on reef sharks at large spatial scales (hundreds of km) that might enable managers to assess the status of shark populations in the face of future development in this region. Here, we examined the occurrence, abundance and behaviour of apex (Galeocerdo cuvier, Carcharhinus plumbeus) and reef (C. amblyrhynchos, C. melanopterus, Triaenodon obesus) sharks using > 1200 deployments of baited remote underwater stereo-video systems (stereo-BRUVs) across > 500 km of coastline. We found evidence for species-specific influences of habitat and fishing activities on the occurrence (probability of observation), abundance (MaxN) and behaviour of sharks (time of arrival to the stereo-BRUVs and likelihood of feeding). Although the presence of management zoning (No-take areas) made little difference to most species, C. amblyrhynchos were more common further from boat ramps (a proxy of recreational fishing pressure). Time of arrival for all species was also influenced by distance to boat ramp, although patterns varied among species. Our results demonstrate the capacity for behavioural metrics to complement existing measures of occurrence and abundance in assessing the potential impact of human activities on shark populations.
Highlights
Quantifying the drivers of population size in reef sharks is critical for the development of appropriate conservation strategies
Recent modelling studies combining data from acoustic telemetry and baited remote underwater video systems (BRUVs) across 36 countries suggest that the median width of No-Take Areas in coral reef systems (9.4 km) would need to be increased by five times and be accompanied by strict enforcement in order to sufficiently protect populations of common reef-associated shark species, such as whitetip (Triaenodon obesus), blacktip (Carcharhinus melanopterus), and grey (C. amblyrhynchos) reef s harks[13]
The standard deviation of the height and structural complexity of the substrate The total reef cover, which is the sum percentage cover of habitat that was classified as reef, sponges, ascidians and macroalgae Factor describing the depth of the stereo-BRUV deployment The minimum Euclidean distance from the stereoBRUV deployment to the closest boat ramp in metres
Summary
Quantifying the drivers of population size in reef sharks is critical for the development of appropriate conservation strategies. Sharks are top-order predators that play important roles in the shallow water ecosystems of reefs, embayments and estuaries throughout tropical and temperate oceans by transferring energy and predation risk across seascapes[1,2,3,4,5] The coasts bordering these shallow habitats are often centres of human population and activities, notably tourism, recreational and commercial fishing, and industrial development (ports, mining facilities etc.). Recent modelling studies combining data from acoustic telemetry and baited remote underwater video systems (BRUVs) across 36 countries suggest that the median width of No-Take Areas in coral reef systems (9.4 km) would need to be increased by five times and be accompanied by strict enforcement in order to sufficiently protect populations of common reef-associated shark species, such as whitetip (Triaenodon obesus), blacktip (Carcharhinus melanopterus), and grey (C. amblyrhynchos) reef s harks[13]. The standard deviation of the height and structural complexity of the substrate The total reef cover, which is the sum percentage cover of habitat that was classified as reef, sponges, ascidians and macroalgae Factor describing the depth of the stereo-BRUV deployment The minimum Euclidean distance from the stereoBRUV deployment to the closest boat ramp in metres
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