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. 2022 Jan 14;12(1):728.
doi: 10.1038/s41598-021-04024-x.

Drivers of variation in occurrence, abundance, and behaviour of sharks on coral reefs

E Lester  1   2   3 , T Langlois  4   5 , I Lindgren  4   5 , M Birt  6   5 , T Bond  4   5 , D McLean  6   4   5 , B Vaughan  6   5 , T H Holmes  6   7 , M Meekan  6   5
Affiliations

Drivers of variation in occurrence, abundance, and behaviour of sharks on coral reefs

E Lester et al. Sci Rep. .

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.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Map of BRUVs deployments in north-west Australia. Colour of circles indicates whether the BRUVs was deployed inside a No-Take Area (red) or in an area where fishing is permitted (Blue). Figure was generated using R using ggplot2 and ggmap.
Figure 2
Figure 2
Importance scores based on summed AIC weights from full subsets analysis exploring the influence of five variables on (a) probability of occurrence, (b) abundance and (c) time of arrival on BRUVs, and (d) likelihood fedfor each shark taxa. The ‘X’ symbols indicate variables that were included in the most parsimonious models (See Table 1). Figure was generated using R using ggplot2.
Figure 3
Figure 3
Map of stereo-BRUVS deployments in north-west Australia (indicated by grey open circles. Colour of circles indicates whether the stereo-BRUVS was deployed inside a No-Take Area (red) or in an area where fishing is permitted (Blue). Size of the circle shows the MaxN of apex sharks (Galeocerdo cuvier, Carcharhinus plumbeus) in each deployment (a). Predicted apex shark probability of occurrence (a,b) as functions of variables present in the most parsimonious models (Table 2) from full-subsets GAMM analysis. Ribbons and error bars represent 95% confidence intervals. Figure was generated using R using ggplot2 and ggmap.
Figure 4
Figure 4
Map of stereo-BRUVS deployments in north-west Australia (indicated by grey open circles. Colour of circles indicates whether the stereo-BRUVS was deployed inside a No-Take Area (red) or in an area where fishing is permitted (Blue). Size of the circle shows the MaxN of Carcharhinus amblyrhynchos in each deployment (a). Predicted C. amblyrhynchos probability of occurrence (b,c,d), abundance (MaxN; e), time of arrival on stereo-BRUVS (f,g,h), and likelihood fed (i, j) as functions of variables present in the most parsimonious models (Table 2) from full-subsets GAMM analysis. Ribbons and error bars represent 95% confidence intervals. Figure was generated using R using ggplot2 and ggmap.
Figure 5
Figure 5
Map of stereo-BRUVS deployments in north-west Australia (indicated by grey open circles. Colour of circles indicates whether the stereo-BRUVS was deployed inside a No-Take Area (red) or in an area where fishing is permitted (Blue). Size of the circle shows the MaxN of Carcharhinus melanopterus in each deployment (a). Predicted C. melanopterus probability of occurrence (b,c), abundance (MaxN; d) and time of arrival on BRUVs (e,f,g) as functions of variables present in the most parsimonious models (Table 2) from full-subsets GAMM analysis. Ribbons and error bars represent 95% confidence intervals. Figure was generated using R using ggplot2 and ggmap.
Figure 6
Figure 6
Map of stereo-BRUVS deployments in north-west Australia (indicated by grey open circles. Colour of circles indicates whether the stereo-BRUVS was deployed inside a No-Take Area (red) or in an area where fishing is permitted (Blue). Size of the circle shows the MaxN of Triaenodon obesus in each deployment (a). Predicted T. obesus probability of occurrence (b,c,d), abundance (MaxN; e) and time of arrival on BRUVs (f,g,h) as functions of variables present in the most parsimonious models (Table 2) from full-subsets GAMM analysis. Ribbons and error bars represent 95% confidence intervals. Figure was generated using R using ggplot2 and ggmap.
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