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Low abundance of sharks and rays in baited remote underwater video surveys in the Arabian Gulf

  • Elasmo Project

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Data on the diversity and relative abundance of elasmobranchs (sharks and rays) in the Arabian Gulf have been limited to fishery-dependent monitoring of landing sites. Understanding the diversity and abundance of sharks and rays is, however, crucial to inform policy and management plans. Baited Remote Underwater Video Surveys (BRUVS) were conducted in 2015–2016 across the United Arab Emirates Arabian Gulf waters encompassing a range of depths and habitat types. Data from 278 BRUVS (757 hours soak time) were analysed to gather information on diversity, relative abundance, species distribution, and habitat associations. Surveys recorded 213 individuals from 20 species of sharks and rays at 129 stations. The frequency of occurrence of species usually discarded by fishers such as the Arabian carpetshark (Chiloscyllium arabicum) and stingrays (Himantura spp.) was high, accounting for 60.5% of observed elasmobranchs. Despite the large survey area covered and extensive sampling effort, the relative abundance of sharks and rays was low at 0.28 elasmobranchs per hour, 0.13 sharks per hour, and 0.15 rays per hour. This CPUE was reduced to one of lowest recorded abundance on BRUVS from around the world when removing the two discarded species from the analysis (0.11 elasmobranchs per hour). These results likely reflect the intense fishing pressure and habitat loss contributing to population declines of many elasmobranchs in the Arabian Gulf. Findings provide a baseline for future work and can support the design of conservation strategies for sharks and rays in the UAE.
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SciEntific RepoRts | (2018) 8:15597 | DOI:10.1038/s41598-018-33611-8
Low abundance of sharks and rays
in baited remote underwater video
surveys in the Arabian Gulf
Rima W. Jabado
1,2, Shamsa M. Al Hameli1, Edwin M. Grandcourt1 & Shaikha S. Al Dhaheri1
Data on the diversity and relative abundance of elasmobranchs (sharks and rays) in the Arabian Gulf
have been limited to shery-dependent monitoring of landing sites. Understanding the diversity and
abundance of sharks and rays is, however, crucial to inform policy and management plans. Baited
Remote Underwater Video Surveys (BRUVS) were conducted in 2015–2016 across the United Arab
Emirates Arabian Gulf waters encompassing a range of depths and habitat types. Data from 278 BRUVS
(757 hours soak time) were analysed to gather information on diversity, relative abundance, species
distribution, and habitat associations. Surveys recorded 213 individuals from 20 species of sharks and
rays at 129 stations. The frequency of occurrence of species usually discarded by shers such as the
Arabian carpetshark (Chiloscyllium arabicum) and stingrays (Himantura spp.) was high, accounting for
60.5% of observed elasmobranchs. Despite the large survey area covered and extensive sampling eort,
the relative abundance of sharks and rays was low at 0.28 elasmobranchs per hour, 0.13 sharks per hour,
and 0.15 rays per hour. This CPUE was reduced to one of lowest recorded abundance on BRUVS from
around the world when removing the two discarded species from the analysis (0.11 elasmobranchs per
hour). These results likely reect the intense shing pressure and habitat loss contributing to population
declines of many elasmobranchs in the Arabian Gulf. Findings provide a baseline for future work and can
support the design of conservation strategies for sharks and rays in the UAE.
Populations of many species of elasmobranchs (sharks and rays) have drastically declined worldwide due to over-
shing and habitat loss leading to growing concerns over their long-term sustainability1,2. Our understanding of
population trends and ecology of these species largely relies on a combination of shery-dependent sources (catch
per unit eort (CPUE)) or extractive shery-independent techniques (e.g., trawl, gillnet, and longline surveys) to
estimate relative abundance3. ese methods form the basis of sheries management but can result in abundance,
catchability, and size selectivity biases4,5. Furthermore, these approaches have a limited ability to survey high
complexity habitats such as coral reefs, do not provide accurate information on non-target species of the various
sheries sampled (i.e., bycatch), and oen fail to record rare and threatened species46.
Beyond the range of commercial and recreational sheries, fundamental information pertaining to diversity,
distribution, and abundance estimates of sharks and rays is crucial for the development of eective management
and conservation initiatives7,8. However, data collection for these species is especially dicult because most are
highly mobile, have ontogenetic shis in habitat preferences, and have broad geographic ranges9,10. Although
there are limited resources and funding to undertake such large scale sampling, the prioritisation of these data is
critical to sheries management and to evidence-based conservation planning7.
A growing number of studies have considered alternative methods to independently assess elasmobranch pop-
ulations and reduce current data gaps6,11. e baited remote underwater video system (BRUVS) technique is now
established as a cost-eective, non-extractive means of providing a standardized, non-invasive, non-extractive,
and non-destructive shery-independent sampling method to (1) estimate the relative abundance of elasmo-
branchs across geographically wide areas as well as a range of habitats and depths that might otherwise be inac-
cessible; (2) provide estimates of species richness; (3) analyse species-specic behaviours; and (4) determine
size and biomass when using stereo-cameras4,5,8,1116. is method uses bait to attract individuals into the eld
of view of a camera so that species can be identied and individuals counted. is approach oen complements
other traditional methods to enhance the scope and capability of monitoring and stock assessment programs13.
1Environment Agency - Abu Dhabi, P.O. Box 45553, Al Mamoura Building, Murour Road, Abu Dhabi, United Arab
Emirates. 2Gulf Elasmo Project, P.O. Box, 29588, Dubai, United Arab Emirates. Correspondence and requests for
materials should be addressed to R.W.J. (email:
Received: 4 April 2018
Accepted: 28 September 2018
Published: xx xx xxxx
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Indeed, studies indicate that BRUVS produce similar relative abundance estimates and species composition to
other shery-independent techniques such as longline surveys5, even though a greater amount of replicates and
amount of time might be required12.
e Arabian Sea and its adjacent waters has recently been highlighted as one of the regions with the most
threatened shark and ray populations in the world17. Much of the data available from the region, and particularly
in the Arabian Gulf, stem from shery-dependent trawl research surveys or monitoring of landings at various
sites (e.g.,18,19). Here, we report on the results from the rst BRUVS to be deployed in the Arabian Gulf waters
of the United Arab Emirates (UAE) with the aim to (1) assess the relative abundance of sharks and rays across
UAE Gulf waters using shery-independent methods; (2) collect data on shark and ray distribution patterns and
habitat associations; and (3) investigate how factors such as season, depth, habitat, and geographic stratum can
inuence the presence of sharks and rays.
Fisheries Resource Assessment Surveys (FRAS) (see Methods for details) were undertaken in May-June 2015,
April to June 2016, and October to December 2016. A total of 283 BRUVS were deployed during this period. Of
these, 278 sites were used in the analysis (Fig.1a); four were discarded due to inadequate visibility (<1.5 m) and
one BRUVS unit was stolen (Fig.2). e total number of video hours was 757.2 hours with a minimum of 64 min-
utes, a maximum of 3.2 hours, and a mean deployment time of 2.1 hours (±0.44 hours SD). All deployments were
spread throughout daylight hours from 06.55–18.15 hrs. Deployment site depths ranged from 1 to 41 m, with a
mean sampling depth of 16.6 m (±8.5 m SD). Details of deployments based on the various factors used in the
analysis are provided in Table1.
Species richness and diversity. Two-hundred and thirteen individual sharks and rays were observed in
which 99 sharks and 114 rays were recorded (Fig.1, Table2). From the 278 deployments, sharks and rays were
observed on 129 (46.4%) of the BRUVS with 64 deployments (23%) recording sharks, and 88 (31.6%) recording
rays. Of the identied individuals (82.4% of individuals observed), a total of 20 shark and ray species, belonging
to eight families from 15 genera were recorded (Fig.3). ese included nine species of sharks from two families
and ve genera and 11 species of rays from six families and 10 genera (Table2). is represents 29.4% of elasmo-
branch species known to occur in Arabian Gulf waters (32 shark species of which 28.1% were observed and 36
ray species of which 30.5% were observed). e cumulative curve indicates that aer approximately 300 hours of
soak time, we had adequately sampled species richness and few additional species were recorded in the remaining
survey time (Fig.4).
e frequency of occurrence of most species was low except for Chiloscyllium arabicum and Himantura spp.
that dominated during the surveys. ese were the most frequently observed species accounting for 60.5% of all
elasmobranchs, 49.5% of identied sharks, and 70.1% of identied rays, respectively. Additional dominant shark
species observed included the whitecheek shark (Carcharhinus dussumieri) (17.2% of identied individuals and
the highest MaxN recorded of 3 sharks in one video frame) and the spottail shark (C. sorrah) (16.2% of identied
individuals). For rays, H. leoparda and Pastinachus spp. accounted for 6.1% and 5.3% of identied rays, respec-
tively. Most species were only recorded once throughout the surveys including the pigeye shark (C. amboinensis),
sharptooth lemon shark (Negaprion acutidens), Halavi guitarsh (Glaucostegus halavi), and the blotched fantail
ray (Taeniurops meyeni). A total of 16 sharks and rays recorded could not be identied due to their distance from
the BRUVS unit.
It was not possible to accurately estimate lengths of individual sharks and rays, especially if these were
observed in the distance. However, at proximity, the majority of sharks (97.9%) were notably smaller than the bait
arm (1.5 m). e majority of Himantura spp. for which we were able to record an estimate of size (n = 68) were
between 50 cm and 100 cm DW (76.4%) with 8.8% larger than 100 cm DW, 76.4% between 50 cm and 100 cm
DW, and 5.8% smaller than 50 cm DW. e largest shark recorded was C. amboinensis at over 150 cm TL while
the largest ray was a smoothnose wedgesh (Rhynchobatus laevis) estimated at over 200 cm TL. e smallest rays
were estimated at around 50 cm TL. Sex could only be determined for 56 Himantura spp. of which 60.7% were
male and 39.3% were female.
Analysis of tapes showed there was no apparent relationship between soak time and the probability of a shark
or ray appearing in the video. Individuals were sighted from the second minute (2.6 mins) of deployment and
until 160.5 mins had elapsed with a mean number of 59.1(±41.4 SD)minutes elapsed to rst sighting.
CPUE. Overall, the CPUE obtained by BRUVS surveys was relatively low (0.28 elasmobranchs per hour, 0.13
sharks per hour, and 0.15 rays per hour) (Fig.5). is CPUE was signicantly reduced when excluding obser-
vations of C. arabicum and Himantura spp. from the analysis (0.11 elasmobranchs per hour and 0.06 sharks per
hour and 0.04 rays per hour respectively). Dierences in the relative abundance of elasmobranchs, sharks, rays,
C. arabicum and Himantura spp. based on Season, Depth, Habitat, and Strata are presented in Fig.6(a–e) and
is CPUE recorded for the southern Arabian Gulf was between one to two orders of magnitude lower than
published estimates obtained from reef systems in French Polynesia, Australia, Fiji, the Bahamas, and Indonesia
is survey is the rst to estimate the relative abundance of sharks and rays using BRUVS in the Arabian Gulf and
across the whole of UAE Gulf waters. It allowed a cost-eective and rapid means to sample across a broad spatial
scale and range of habitats. Results clearly indicate a low relative abundance of elasmobranchs across the south-
ern Arabian Gulf with CPUE levels up to two orders of magnitude lower than those recorded using comparable
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BRUVS techniques in other regions of the world (e.g., Maldives20, French Polynesia6, Western Australia5, and
Sudan21). When removing C. arabicum and Himantura spp. from our analysis, species known to be discarded
by shers in the UAE18,22, our CPUE is reduced by more than half and ranges closer to the alarmingly low CPUE
results from the northern Saudi Arabian Red Sea21. While there are few historical baselines of elasmobranch
abundance from the Arabian Gulf, several studies have already highlighted the increasing shing pressure on
these species in the region with population declines as well as changes in the species composition and sizes of
individuals landed (e.g.18,19). Overshing is the most plausible explanation for the almost complete absence of
large sharks during these surveys and the overall low diversity of species. ese ndings are consistent with the
hypothesis that sharks and rays in the Arabian Gulf and broader Arabian Sea and adjacent waters region are
amongst the most threatened in the world17. Despite the UAE having developed legislation to regulate shark
shing (including species-specic protections), most species (especially sharks) are still landed as bycatch due to
an overlap between the seasonal shark shing ban and open gillnet shing season22. Unsustainable shing and
overexploitation of elasmobranch resources, coupled with weak enforcement of shing policies, are widespread
in the region and these low CPUE numbers are likely a reection of stocks that have been depleted from over two
decades of overshing21,23.
Only 29.4% of elasmobranch species known from sheries-dependent surveys to occur in Arabian Gulf waters
were recorded using BRUVS17,24,25. Other surveys along the Great Barrier Reef in Australia, Indonesia, and South
Africa also recorded less than 50% of known elasmobranch diversity15,26,27. is low diversity in BRUVS could be
due to several factors including the behavior of animals in the presence of bait, or environmental variables such
Figure 1. Map of the United Arab Emirates showing locations of (a) stations (n = 278) where baited remote
underwater video surveys were deployed = , (b) location of shark = and ray = sightings, and (c) location
of Arabian carpetshark Chiloscyllium arabicum = and stingray Himantura spp. = sightings.
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as depth gradients or habitats surveyed15,26. Firstly, our BRUVS recorded during the day and some elasmobranch
species exhibit diel changes in behavior and activity28,29. For example, many shark species are less active during
the day than at night when shers set various shing gear (e.g., gillnets or longlines) and catch large quantities of
sharks22,29,30. Furthermore, shers tend to have much longer soak times (oen over 12 hours) and cover large areas
and therefore are more likely to capture sharks and rays during foraging trips27. Also, BRUVS might be biased
towards species attracted to the bait15, while net shing captures individuals that are not bait-dependent27. We do
however recognize that of the 16 unidentied animals recorded on our BRUVS, 14 were rays, highlighting that
the species richness of rays could be higher than what is reported here.
Figure 2. Baited Remote Underwater Video Survey unit with GoPro Hero 4 mounted, bait arm, and bait bag.
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Vessel and logistical constraints during FRAS prevented us from sampling inshore shallow lagoons and
mangrove forests, thus potentially underestimating the abundance of species occurring in these areas. Several
ray species have been observed in shallow water lagoons within UAE waters31 while some shark species utilize
mangroves as nursery areas in other regions of the world (e.g.,32). Nevertheless, we sampled across the depths
gradients of UAE waters (1 to 41 m), in many shallow areas, as well as structurally complex habitats (seagrass
beds, so-sediment inter-reef habitats, macro-algae), areas that also likely provide ideal habitats for many elas-
mobranch species. We found no signicant dierences in the abundance of elasmobranchs for each of these
variables. It is unlikely that depth inuenced the abundance of sharks, a result that is consistent with those from16
and33 who suggest that the lack of dierence in abundance with depth could be due to their attraction to the bait
along with their capability to disperse between dierent depths. Furthermore, several studies have shown that
sharks are oen more common at oshore sites than in inshore coastal habitats (e.g.,15). In the UAE, shers have
conrmed they travel to deeper waters to catch sharks as they have practically disappeared from inshore waters
and it is unlikely that the limited sampling in inshore habitats would have signicantly changed our CPUE results
for sharks22. Less information is available on habitat preferences of ray species occurring in UAE waters. Further
Survey period n BRUVS
Depth Habitat Strata
10 m >10 m Mud Sand Other West Central East
Spring 2015 26 26 0 0 2 24 26 0 0
Spring/Summer 2016 134 49 85 58 38 38 107 23 4
Fall/Winter 2016 118 50 68 51 51 16 30 53 35
Tot a l 278 125 153 109 91 78 163 76 39
Table 1. Summary of the number of Baited Remote Underwater Surveys (n BRUVS) completed in 2015 and
2016 by Depth, Habitat and Strata.
Common name Species name Σ MaxN % Occurrence Depth Habitats (MaxN) Seasons (MaxN) Size range
Pigeye shark Carcharhinus amboine nsis 1 0.5 11 M (1) FW (1) >150 TL
Whitecheek shark Carcharhinus dussumie ri 17 8 11–24 M (3), S (2), O (1) SS (1)– FW (3) <100 TL
Blacktip shark Carcharhinus limbatus 6 2.8 9–24 M (2), O (1) SS (1) – FW (2) <100 TL
Blacktip reef shark Carcharhinus melanopte rus 2 0.9 1–6 O (1) SS (1) <100 TL
Spottail shark Carcharhinus sorrah 16 7.5 3–30 M (2), S (2), O (1) SS (2) – FW (2) <100 TL
Sliteye shark Loxodon macror hinus 3 1.4 13–20 M (1), S (1), O (1) SS (1)- FW (1) <100 TL
Sharptooth lemon shark Negaprion acutidens 1 0.5 6 O (1) SS (1) >100 TL
Milk Shark Rhizoprionodon acutus 4 1.9 13–20 M (1) SS (1)- FW (1) <100 TL
Whaler shark Carcharhinus sp. 2 0.9 20–22 M (1), O (1) FW (1) <100 TL
Hemiscyllidae Arabian carpetshark C hiloscyllium arabicum 49 23 3–23 M (2), S (1), O (3) SS (3) – FW (2) <100 TL
Total sharks 99 47.3
Aetobatidae Spotted eagle ray Aetobatus ocellatus 6 2.8 4–20 S (1), O (1) SS (1) n/a
Leopard whipray Himantura leoparda 7 3.3 11–22 M (1), S (1), O (1) SS (1) – FW (1) 80–100 DW
Reticulate whipray Himantura uarn ak 67 31.5 5–37 M (2), S (3), O (2) SS (2) – FW (3) 40–>100 DW
Pink whipray Pateobati s fai 2 0.9 17–29 M (1) FW (1) 40–100
Cowtail ray Pastinachus sp. 6 2.8 5–13 M (1), S (1), O (1) SS (1) – FW (1) 40–100
Blotched fantail ray Taeniurops meyeni 1 0.5 19 S (1) SS (1) 60–80 DW
Glaucostegidae Halavi guitarsh Glaucostegus halavi 1 0.5 22 M (1) SS (1) >100 TL
Gymnuridae Longtail buttery ray Gy mnura poecilura 1 0.5 17 S (1) SS (1) 30–40 DW
Bowmouth guitarsh Rhina ancylostoma 1 0.5 14 0 (1) SS (1) >100 TL
Smoothnose wedgesh Rhynchobatus laevis 2 0.9 17–25 S (1) SS (1) >200 TL
Wedgesh Rhynchobatus sp. 1 0.5 21 M (1) FW (1) 100–200 TL
Rhinopteridae Cownose ray Rhinoptera sp. 3 1.4 5–14 O (2) SS (2) 40–100 DW
Unidentied Himantura s p. 14 6.6 5–37 M (1), S (1), O (2) SS (2) – FW (1) n/a
Total rays 114 52.7
TOTALS 213 100
Table 2. Summary of results of Baited Remote Underwater Video Surveys (BRUVS) with a summary of shark
and ray species observed during deployments, abundance (sum (Σ) of MaxN and % MaxN), depth ranges (m),
habitat associations (S – Sand, M – Mud, O – Other; and MaxN by type), seasons (SS – Spring/Summer, FW –
Fall/Winter; and MaxN for each), and estimated size ranges (cm) as total length (TL) or Disc Width (DW). n/a
indicates individuals did not approach the bait arm to allow for size estimates.
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research in these shallow inshore habitats is warranted to determine which are critical sites for elasmobranchs
including breeding aggregation, mating, and nursery areas.
While gear selectivity or environmental variables could also be a reason for not sampling the overall diversity
of species in UAE waters, we argue that the core reason many species were not present in our surveys is due of their
current low abundance in these waters. Indeed, while the relative abundance of shark species varied from that
recorded during shery-dependent surveys in the UAE, except for C. arabicum, species diversity was consistent
with dominant species landed by shers across the country. Interviews with shers, as well as landing site surveys
conrm that carpet sharks are not targeted by shing activity in the UAE and are usually discarded18,22. In the UAE,
over 90% of landings consist of the spottail (C. sorrah), milk (Rhizoprionodon acutus), common blacktip shark
(C. limbatus), whitecheek shark (C. dussumieri) and slit-eye shark (Loxodon macrorhinus) sharks, all of which
Figure 3. Images of elasmobranchs captured by the baited remote underwater video systems in the Arabian
Gulf, (a) spottail shark Carcharhinus sorrah, (b) leopard whipray Himantura leoparda, (c) smoothnose
wedgesh Rhynchobatus laevis.
Figure 4. Cumulative number of elasmobranchs (), sharks ( ), and rays ( ) recorded for each 50-hour
soak time interval on the baited remote underwater video systems in the Arabian Gulf.
Figure 5. Mean relative abundance (MaxN h1 ± SE) of Elasmobranchs, Sharks, Rays, Arabian carpetshark
Chiloscyllium arabicum, and stingrays Himantura spp. determined by baited underwater video surveys.
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were observed in this study and therefore conrming their prevalence in these waters18. Indeed, because BRUVS
use baits that attract sharks, they probably sample those species likely to be most aected by shing activity16.
On the other hand, the diversity and abundance of ray species recorded here were dierent than those recorded
during landing site surveys. Landings data indicate that the most abundant taxa are the cownose rays (Rhinoptera
spp.) (59.4% of ray landings), eagle rays (Aetomylaeus spp.) (20.6%), and wedgeshes, Rhynchobatus spp. (10.5%)34
(Jabado, unpubl. data). While several species of rays were recorded, Himantura spp. clearly dominated in our
survey. is dierent species composition could be due to the fact that shers generally discard ray catches in the
UAE unless they are netted in large numbers22. is indicates that BRUVS have the potential to provide a better
indication of diversity and abundance than shery-dependent surveys for unwanted and discarded catch.
An understanding of habitat associations at the species level and over large spatial gradients can be a valuable
approach to detect important areas for elasmobranch conservation, as well as reveal complex ecological processes
such as connectivity within and across ecosystems15. Due to the low abundance of most species observed, it was
dicult to identify spatial, seasonal, or habitat association patterns and this information was only discerned for C.
arabicum and Himantura spp. Chiloscyllium arabicum sharks exhibited a strong association with shallow waters of
the western region where complex habitats such as coral assemblages and seagrass beds are most prevalent. On the
other hand, Himantura spp. were more common in the deeper waters of the eastern zone characterized by areas
of sand and mud with little structurally complex habitats. ese results are likely due to the habitat preferences
of these two species groups which is oen due to the availability of feeding and refuge sites for prey species25,35.
Further studies are needed in the Arabian Gulf to elucidate habitat associations and use for the majority of spe-
cies occurring in these waters. ese data can then support assessments of the risk of species to shing and/or
habitat degradation.
Figure 6. Mean relative abundance (MaxN h1 ± SE) of Elasmobranchs, Sharks, Rays, Arabian carpetshark
Chiloscyllium arabicum, and stingrays Himantura spp. determined by baited underwater video surveys in
relation to Season (SS: Spring/Summer, FW: Fall/Winter), Depth (Shallow: 10 m, Deep: >10 m), Habitat (Sand,
Mud, Other), and Strata (West, Central, East). * Indicates a signicant dierence (p < 0.05) between groups.
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e species-level identication of individuals and the determination of sizes and sex using BRUVS are chal-
lenging and common limitations5,12,15,27,36. On some occasions animals did not approach the camera and we were
therefore only able to identify 82.4% of observed individuals. is was particularly challenging with some species
of rays that need closer morphological examination to separate between similar species. Furthermore, while clasp-
ers of mature males are usually visible, discerning the sex of females or sub-adult males was challenging since it
depends on the behavior of the animals in front of the camera12. e large majority of the animals observed here
were small-bodied species with maximum total lengths or disc widths of less than 100 cm (e.g., C. arabicum,
R. acutus, C. dussumieri, and longtailed buttery ray G. poecilura)24,25,35 and it was therefore not possible to determine
maturity levels. For some of the larger-bodied animals (e.g., C. sorrah, C. limbatus, H. uarnak, R. laevis), even though
the depth of view of horizontal look-outward systems does not provide a good reference for measurements, the
length of the bait arm provided a point of perspective as a scale bar allowing for coarse estimations of sizes13. In future
studies, we recommend the use of stereo-video techniques to examine relative abundance at an intra-species resolu-
tion as they can provide accurate length and biomass estimates12,37,38. Indeed, the use of length-frequency estimates
for selected commercially important species can provide an additional useful metric for long-term monitoring.
It is important to note that there are a number of biases associated with comparing BRUVS studies from
around the world including the sampling design and deployment of units (i.e., time of day, depths), the type
and quantity of bait used, and soak times6,21. ese can highly inuence estimates of relative abundance and
species richness. While this BRUVS study was not eectively designed to investigate the occurrence and distribu-
tion of sharks and rays, deployment times, type and amount of bait, and survey time frames generally exceeded
those reported for elasmobranchs from around the world5,12,16,21,27,30. One study39 shows that sampling precision
is improved with increasing soak times as it likely enhances the probability of the bait plume intersecting indi-
viduals as they move around and attracts them to the BRUVS unit. Overall, an optimal 60-minute deployment
time is proven to provide an accurate representation of species assemblages and is adequate to record 95% of
species14,37, although sightings can continue to increase until aer 180 mins of deployment21. It has been sug-
gested that it takes longer for sharks to appear in the video when their abundance is low4. In our study, soak time
df X2pdf X2pdf X2p df X2pdf X2p
Season (SS × FW) 1 4.322 0.038 1 4.421 0.036 1 0.242 0.623 1 0.702 0.000 1 12.513 0.402
Depth (S × D) 1 0.355 0.551 1 1.772 0.183 1 6.526 0.011 1 7.194 0.007 1 9.047 0.003
Habitat (S × M × O) 2 0.755 0.686 2 8.968 0.011 2 2.250 0.325 2 12.809 0.002 2 6.947 0.031
Strata (W × C × E) 2 1.109 0.574 2 15.327 0.000 2 5.556 0.062 2 13.940 0.001 2 9.161 0.010
Pairwise tests UpUpUpUpUp
(S × M) 4685 0.533 4337 0.038 4548 0.280 4831 0.689 4743 0.594
(S × O) 3306 0.401 2848 0.002 3175 0.157 2927 0.003 2954 0.010
(M × O) 4122 0.788 3918 0.305 4075 0.639 3526 0.004 3646 0.030
(W × C) 5987 0.651 5417 0.044 5336 0.035 5431 0.018 5155 0.005
(W × E) 2940 0.422 2274 0.000 2753 0.104 2515 0.002 2724 0.049
(C × E) 1318 0.289 1261 0.022 1472 0.946 1365 0.073 1455 0.849
Table 3. Results of ANOVA testing the eect of Season (SS: Spring/Summer, FW: Fall/Winter), Depth (Shallow:
10 m, D eep: >10 m), Habitat (S: Sand, M: Mud, O: Other), and Strata (W: West, C: Central, E: East) on the
relative abundance of Elasmobranchs, Sharks, Rays, the Arabian carpetshark (Chiloscyllium arabicum) and
stingrays (Himantura spp.); df = degrees of freedom; bold p values denotes signicance at p < 0.05.
Figure 7. Comparison of mean relative abundance (MaxN h1) published from BRUVS studies from around
the world for sharks in shed areas (black), sharks in no-take zones (light grey), and elasmobranchs in shed
areas (dark grey). For the UAE, the dark grey column represents the CPUE of sharks and rays aer removing the
Arabian carpetshark (Chiloscyllium arabicum) and stingrays (Himantura spp.) from the analysis.
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varied between a minimum of one hour and up to over 3 hours, and our cumulative species curve shows that few
new species were recorded aer 300 hours of soak time, indicating that we adequately sampled abundance and
species diversity in southern Arabian Gulf waters. We do acknowledge that water quality and visibility is likely
the greatest limitation to BRUVS13,15. While lack of visibility due to lighting at depth is oen not an issue in the
shallow waters of the Arabian Gulf, the vast majority of this body of water is characterized by muddy substrates40.
is aected visibility at certain sites when large quantities of teleost sh aggregated and created a ‘mud’ plume.
Several stations had to be removed from this study due to the inability to see the bait bag (1.5 m from the camera).
Some results show that there is a marginal, non-signicant eect of underwater visibility on the performance of
BRUVS with performance dropping only at the lowest visibility (about 1 m)41. erefore, even though visibility
might have been variable, there were no signicant dierences in CPUE between sand and mud habitats and
visibility is unlikely to have aected our overall CPUE. Overcoming this limitation in Arabian Gulf waters might
require the development of li-bag systems or sampling using cameras from above.
In conclusion, this study has provided valuable data to complement existing sheries-dependent information
available in the UAE. It conrms that the BRUVS sampling technique is useful to examine the diversity, relative
abundance, and habitat associations of elasmobranchs across broad spatial scales, especially in areas where the
use of conventional sheries-independent sampling tools would be dicult to implement. ere is scope for the
future use of this data as a baseline to monitor changes in the relative abundance of species while allowing the
examination of changes in species diversity and composition over time in response to natural and anthropogenic
drivers. However, combining dierent techniques for monitoring, including shery-dependent and independent
methods, will prove more appropriate to fully dene species richness and assemblages in waters where shing
pressure is intense, sheries discards are prevalent (e.g., carpet sharks and rays), or where rare species are known
to occur. Finally, as highlighted from results in Australia29, if management strategies were to be developed and
implemented to reverse stock declines in the Arabian Gulf, BRUVS can allow measurements of species-specic
recovery patterns and demonstrate the ecacy of management strategies.
Study area. e Arabian Gulf is a sub-tropical and semi-enclosed basin characterized by a wide range of habitats
including coral reefs, mangroves, sandy bays, seagrass beds, and so-sediment habitats40,42. is shallow sea, con-
nected to the Indian Ocean through the narrow Strait of Hormuz, is unique in its extreme environmental conditions.
With an average depth of 35 m, salinity levels are high and oen exceed 45 parts per thousand, while sea surface
temperatures can uctuate between 12 °C in winter to over 36 °C in summer40. e UAE is a coastal country located
on the southern side of the Arabian Gulf with an Exclusive Economic Zone (EEZ) of 58,292 km2. It has a coastline of
approximately 650 km facing the Arabian Gulf, and approximately 70 km bordering the Sea of Oman (Fig.1).
Sampling technique. e BRUVS dataset used here was not collected specically to examine shark and
ray diversity and abundance patterns. ese surveys were conducted as a component of the Fisheries Resources
Assessment Survey (FRAS) to assess the abundance and status of demersal sheries resources in UAE Gulf waters.
BRUVS were deployed from surface vessels during daytime hours at randomly generated stations (New Zealand
National Institute of Water and Atmospheric Research (NIWA) Random Station Generator) across UAE Gulf
waters. To avoid issues with maritime boundaries, surveys considered a 12 nautical mile (nm) exclusion zone
inside of the UAE Exclusive Economic Zone and extended to 15 nm around the island of Abu Musa (Fig.1a).
Additionally, several restricted locations were excluded from the sampling (e.g., oilelds and concession areas,
major shipping lanes and channels) as well as shallow lagoon areas or mangrove forests occurring at depths of
1–3 m that could not be accessed with FRAS vessels.
BRUVS were tted with a GoPro Hero 4 + black high denition camera, set to the standard settings of high
denition video quality (1080), super-wide frame and 25 frames per second) to ensure a full view of the seaoor,
enclosed in a frame and mounted on a steel rod of 1.2 m height (Fig.2). A weighed down (with 2 kg of dive weight
on each side) 1 × 1 m piece of thick mesh (mesh dimension 2.5 × 2.5 cm) was used as a base frame for each
BRUVS unit to stabilize it and ensure a consistent eld of view. A bait arm made of two crossed 25 mm diameter
PVC pipes was placed 1.5 m away from the center of the mesh. e bait consisted of 2 kg of fresh Indian oil sar-
dines (Sardinella longiceps) in a wire mesh bag, chopped to maximize dispersal of the sh oil. BRUVS units were
lowered to the sea bed from the boat using a rope with a buoy placed at the surface to facilitate manual retrieval.
Cameras were set to record continuously for at least a 60 minute period.
Video and data analysis. Species richness and relative abundance estimates of sharks and rays were recorded
during the review of the video footage using Apple Quicktime by the rst two authors. e start time of the video
was recorded when BRUVS landed on the seaoor and settled in one location. To avoid repeat counts of individual
sharks and rays continuously re-entering the eld of view, the maximum number of individuals of the same species
appearing at the same time (MaxN) was used as a relative abundance measure43. MaxN is a conservative estimate
of abundance in high density areas43,44 and was recorded for ve categories: Elasmobranchs (sharks and rays com-
bined), Sharks, Rays, Arabian carpetshark (Chiloscyllium arabicum), and stingrays (Himantura spp.) which consisted
of the reticulated whipray (H. uarnak) and the leopard whipray (H. leoparda). Deployment time, species, sex (if vis-
ible), time of rst sighting, time of each subsequent sighting, MaxN, time of MaxN, and benthos type were recorded
in all videos. Depth was determined using built-in vessel depth sounders at each site. Samples were discarded from
analysis if horizontal visibility was low (<1.5 m), estimated by means of visibility of the bait bag.
Species were identied to the lowest possible taxon. If identication could not be condently conrmed, then
individuals were recorded under the closest genus or family name. For example, this occurred for individuals of
the genus Pastinachus and Rhinoptera, where two look-alike species of each occur in Arabian Gulf waters and
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SciEntific RepoRts | (2018) 8:15597 | DOI:10.1038/s41598-018-33611-8
need close morphological examination in order to separate them. Furthermore, in some cases, sharks or rays
made distant passes, making it dicult to identify to a family level. No attempts at measurements of individuals
were made but coarse estimates of the total length (TL) or disc width (DW) of each individual were noted to
thenearest 50 cm increment by comparing them with the length of the PVC pipe on the bait arm and individ-
uals were classied as ‘adult’ or ‘juvenile’, based on their size compared to known maturity estimates from the
All statistical analysis was conducted using SPSS (version 23). e catch per unit eort (CPUE), used as a rel-
ative abundance index, was calculated as Max N/hr1 for each species and category. Relative abundance was com-
pared for four factors: Season (Spring/Summer and Fall/Winter), Depth (shallow: 10 m or less and deep, over 10 m),
Geographic strata (West, Central, and East), and Habitat type (Mud (unconsolidated sediment), Sand (consolidated
sand), and Other (other habitats including seagrass, macro-algae, and coral assemblages)) using Kruskal-Wallis
non-parametric rank tests (ANOVA) as CPUE data was found to deviate signicantly from a normal distribu-
tion due to the abundance of 0 values within the data set. Signicant dierences among the groups were further
explored using post-hoc Mann-Whitney U tests. A Bonferroni correction was not applied, given the radical low-
ering of statistical power and increased likelihood of Type II errors associated with this type of correction12,45,46.
e relationship between soak time and the number of species of elasmobranchs, sharks, and rays observed
was evaluated by plotting a species cumulative curve against each 50-hour soak time interval. Finally, the CPUE
was graphically compared to published estimates obtained using similar BRUVS approaches in terms of camera
orientation (vertical to substrate), number of cameras (one at a time), bait type (pilchards or sardines), soak time
(at least 60 mins), and video metrics used (MaxN), from dierent regions around the world6,12,15,16,20,21,26,27,33.
Where more than one study has been conducted in the same region (i.e., Northwest Australia and Indonesia), the
average of all published estimates was depicted21.
Data Availability
e data that support the ndings of this study are available from the Environment Agency–Abu Dhabi but re-
strictions apply to the availability of these data, which were used under license for the current study, and so are
not publicly available. Data are however available from the authors upon reasonable request and with permission
of the Environment Agency – Abu Dhabi.
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e authors would like to thank Environment Agency – Abu Dhabi Management for supporting and funding
the Fisheries Resources Assessment Survey. We gratefully acknowledge the support and involvement of the New
Zealand National Institute of Water and Atmospheric Research team, especially Neil Bagley, Rosemary Hurst,
Keith Michael, Peter Marriott, Bilal Bjeirmi, Peter Mc Millan, Darren Stevens, Warrick Lyon, Darren Parsons, and
Dan MacGibbon in the design of the baited underwater video survey units and their deployment. anks also
go to the crew of RV ‘Bahith I’ and ‘Bahith II’ for their assistance with the eld work. A special thank you to Will
White for conrming the identication of Himantura uarnak and H. leoparda individuals recorded on the videos
and to Maitha M. Al Hameli for providing GIS assistance.
Author Contributions
S.S.A.D. acquired the funding for this project. E.M.G. and S.S.A.D. were in charge of project administration and
provided logistical support. S.M.A.H. and R.W.J. completed the video analysis. R.W.J. wrote the main manuscript
text. R.W.J. and S.M.A.H. prepared all gures. E.D.G. and R.W.J. undertook the statistical analyses. All authors
reviewed and edited the manuscript.
Additional Information
Competing Interests: e authors declare no competing interests.
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... Of the five species belonging to the genus, P. fai (Jordan & Seale) and P. jenkinsii (Annandale) have widespread overlapping distribution while the other species have a narrower home range size which is restricted to Southeast Asia and northern Australia (Last et al. 2016b). So far, a handful of specimens of both species have been reported from the Persian Gulf, the Gulf of Oman and the Arabian Sea (Henderson and Reeve 2011;Almoji et al. 2015;Henderson et al. 2016;Jabado et al. 2018), suggesting that our knowledge of their abundance and genetic characteristics is inadequate. Urogymnus asperrimus (Bloch and Schneider) is the most common and widespread member of its genus, found in Indo-West Pacific waters. ...
... To test whether the low genetic variability might have been caused by a bottleneck effect, well-documented data is required. Both species are economically important in the northwest of the Indian Ocean, either being captured as target species in Sri Lanka, Oman, Pakistan, Qatar, Kuwait, UAE and some parts of Iran (Moore et al. 2010;Almoji et al. 2015;Fernando et al. 2019;Jabado et al. 2018;Henderson et al. 2016;Moore 2012) or as bycatches (Moore 2012). This could be one of the causes of the drastic reduction of their population size (Connallon and Sgrò 2018). ...
... According to Almoji et al. (2015), the occurrence of P. fai in the Persian Gulf is not well known and prior to this study, only one specimen was recorded from Abu Dhabi, UAE. A recent baited remote underwater video survey by Jabado et al. (2018) observed only two specimens of P. fai across the United Arab Emirate waters during one year. In the tree resulting from the BI analysis, the single male specimen clustered with the reference sequence (GN3627, female) from Malaysia. ...
Correct identification of elasmobranch species is crucial for taxonomic and parasitological research. Although molecular barcoding may be the fastest choice to determine the identity of a given species, robust and fast species level identification in the field using morphological characters is essential. During this study, 389 specimens representing seven stingray species (Brevitrygon walga, Himantura leoparda, H. uarnak, Maculabatis randalli, M. arabica, M. gerrardi and Pateobatis fai) were examined from the Persian Gulf and the Gulf of Oman. A 1044 bp fragment of the NADH2 gene was generated for 50 specimens with representatives of all species. To verify the initial morphological identification and to compare intra- and interspecific differences a Neighbor-Joining analysis was conducted using uncorrected p-distances, whereas the Bayesian Inference was used to examine the relationships among taxa. Two species (M. arabica and M. gerrardi) are documented from the Persian Gulf for the first time. The molecular results provide the first known evidence of the sympatric distribution of M. randalli and M. arabica in the north and northwestern Indian Ocean. The results of the Bayesian Inference support the recent divergence of both species. Based on morphological comparisons and molecular support we suggest that the descriptions of M. randalli and M. arabica have been carried out on heterogeneous type series which has led to inconsistency between molecular identification and diagnostic morphological characteristics. Detailed morphological examination revealed that there is a relation between the type and number of denticles on the mid-dorsal surface of the disc and the color pattern of the tail. To address this taxonomic conflict all type materials should be re-examined. The Bayesian Inference tree showed that all specimens from the Persian Gulf and the Gulf of Oman morphologically resembling B. walga were found to group well outside those of the Indian species (B. imbricata) with an average p-distance of 0.097. The low nucleotide differences among the urogymnid taxa (P. fai and H. leoparda) from the Persian Gulf and the Gulf of Oman and their conspecific specimens in the Indo-West Pacific region revealed that philopatric behaviors may cause considerable gene flow among populations.
... Giant guitarfishes and wedgefishes reside preferentially in soft bottom areas of coral reefs and seagrass meadows. Their flattened body is adapted to the benthos, and they mostly swim close to the sea floor or lie concealed within sea-bed sediments (Oh, 2016;Jabado et al., 2018a). However, these habitats face losses and fragmentation effects due to overfishing, pollution, and climate change (Wear, 2016;Unsworth et al., 2018), severely threatening giant guitarfishes and wedgefishes in their natural environment (Jabado et al., 2017;. ...
... When sold fresh, these elasmobranchs can fetch a relatively high price of US$4 per kilogram (Choy CPP & Choo MY, 2020, unpublished data), and a whole wedgefish over 2 m in total length can be sold at prices as high as US$680 (Jabado, 2018) owing to its reputation as good quality meat (Moore, 2017). Together, artisanal and commercial fisheries put extreme pressure on harvested populations (Last, White & Pogonoski, 2008;Dulvy et al., 2014;Jabado et al., 2018a;D'Alberto et al., 2019), with declining catch rates in trawl surveys and reductions in landings reported at fishing ports across the Indo-West Pacific and Indian Ocean despite a substantial increase in fishing effort (Jabado et al., 2018b (Jabado, 2018). The remaining four species in the Glaucostegidae were also added to Appendix II to facilitate enforcement because of difficulties in distinguishing the confamilial species (CITES, 2019a). ...
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• Giant guitarfishes (Glaucostegidae) and wedgefishes (Rhinidae) are some of the most threatened marine taxa in the world, with 15 of the 16 known species exhibiting global population declines and categorized as Critically Endangered according to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. The recent inclusion of all species in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) necessitates more rigorous enforcement by regulatory authorities. • Challenges in regulating the trade of giant guitarfish and wedgefish products due to difficulties in visual identification of processed products and labelling issues impede enforcement. The aim of this study is to characterize the diversity and origins of associated traded products that were commercially available in Singapore, one of the world's top importers and re‐exporters of shark and ray products. • A total of 176 samples of elasmobranch products were obtained between June and December 2019 from fishery ports and various retailers in Singapore. By applying cytochrome c oxidase subunit I gene barcoding, 31 elasmobranch species were detected, with 55% of the species considered threatened (Critically Endangered, Endangered, or Vulnerable) based on the IUCN Red List and 35% of species listed in CITES Appendix II. Four species of giant guitarfishes and wedgefishes were commercially available to consumers in fresh forms of whole fish, fillet, and fin, as well as dried and cooked meats. • DNA barcoding has proven to be an effective tool for identifying elasmobranch products that are impossible to recognize visually and would aid enforcement of CITES trade regulations. This work underscores the urgent need to step up enforcement of marine wildlife regulations and draw public attention to the elasmobranch trade.
... While shark landings may be decreasing slightly (Davidson et al. 2015), ray landings in Indonesia increased in the early 2000s, and they are still caught and sold in markets across the country (White & Dharmadi 2007, Nijman & Nekaris 2014. Intense fishing pressure can have a large negative effect on elasmobranch abundances as seen in the Arabian Gulf (Jabado et al. 2018). In the present study, the opposite was observed for the 2 small-bodied genera of rays. ...
... In the present study, the opposite was observed for the 2 small-bodied genera of rays. Jabado et al. (2018) found a SPUE of 0.15 rays h −1 in a heavily fished environment (SPUE of 0.06 predators h −1 ), whereas our study found a SPUE of > 0.60 rays h −1 in 4 out of 7 sites in Malaysia and Indonesia (SPUE of 0.0 to 0.17 predators h −1 ). This was compared to a SPUE of < 0.15 rays h −1 in 5 out of 7 sites in Australia and Vanuatu, which have relatively low fishing pressure and higher predator abundance (SPUE of 0.20 to 1.48 predators h −1 ). ...
Shark abundances are decreasing on many coral reefs, but the ecosystem effects of this loss are poorly understood. Rays are a prevalent mesopredator in tropical coral reef ecosystems that are preyed upon by top predators like sharks. Studies have suggested reduced predator abundances lead to increases in mesopredator abundance (mesopredator release). We examined the relationship between top predator abundances and the abundance and behaviour of 2 small benthic ray genera using baited remote underwater video systems (BRUVS) across 6 countries. Where predators were more abundant, 2 genera of small benthic rays were sighted less often, possibly because of lower abundances. Small ray behaviour was also significantly affected by predator abundance. Individuals of focal ray species visited BRUVS significantly fewer times at sites with higher predator abundances. Where predators were less abundant, rays spent significantly more time in the video frame, and were more likely to feed from bait bags. In addition to predator abundance, small ray presence was significantly influenced by reef relief and depth. Neotrygon spp. were more abundant on deeper, lower relief habitats, while Taeniura spp. were more prevalent in reef-associated shallow, high relief habitats. Overall, this study found that predator abundance had a significant effect on small benthic ray abundance and behaviour in the presence of BRUVS. Results demonstrate that changes in both abundance and behaviour associated with predator loss may make the interpretation of phenomenon like mesopredator release more difficult to identify unless behavioural effects are considered.
... Recorded footage also provides valuable observations of species' behaviors in their natural environment 20 , which may have a powerful outreach and educational potential 21 . The use of baited remote underwater video stations (BRUVS) is perhaps one of the most accessible, highly replicated, non-destructive and effective tool for quantifying fish assemblages, species-habitat associations and anthropogenic impacts across large spatial scales 19,22,23 . Using bait increases the probability of detecting predators in the environment, since the resulting bait plume can trigger bait-search behaviors in nearby species 24,25 . ...
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Understanding how threatened species are distributed in space and time can have direct applications to conservation planning. However, implementing standardized methods to monitor populations of wide‑ranging species is often expensive and challenging. In this study, we used baited remote underwater video stations (BRUVS) to quantify elasmobranch abundance and distribution patterns across a gradient of protection in the Pacific waters of Costa Rica. Our BRUVS survey detected 29 species, which represents 54% of the entire elasmobranch diversity reported to date in shallow waters (< 60 m) of the Pacific of Costa Rica. Our data demonstrated that elasmobranchs benefit from no‑take MPAs, yet large predators are relatively uncommon or absent from open‑fishing sites. We showed that BRUVS are capable of providing fast and reliable estimates of the distribution and abundance of data‑poor elasmobranch species over large spatial and temporal scales, and in doing so, they can provide critical information for detecting population‑level changes in response to multiple threats such as overfishing, habitat degradation and climate change. Moreover, given that 66% of the species detected are threatened, a well‑designed BRUVS survey may provide crucial population data for assessing the conservation status of elasmobranchs. These efforts led to the establishment of a national monitoring program focused on elasmobranchs and key marine megafauna that could guide monitoring efforts at a regional scale.
... However, Sherman et al. (2018) successfully attracted oriental bluespotted maskray Neotrygon orientalis and bluespotted fantail ray Taeniura lymma to BRUVS baited with pilchards (Sardinella spp.) and slimy mackerel Scomber australiasicus in Malaysian Borneo, and BRUVS deployed by Hanusch (2019) off Mozambique baited with Cape horse mackerel Trachurus capensis attracted bluespotted maskray Neotrygon caeruleopunctata and blotched stingray Taeniurops meyeni. Furthermore, a variety of demersal ray species were recorded on BRUVS baited with Indian oil sardine Sardinella longiceps in UAE waters (Jabado et al. 2018), while H. americanus was abundant on BRUVS deployed in Belize (Bond et al. 2019). Therefore, it seems clear that demersal rays which feed primarily on invertebrates will respond to BRUVS baited with fish, leading to the conclusion that it was the specific type of bait used during the present study, i.e. S. barracuda, that was not strongly attractive to H. americanus. ...
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The present study was undertaken to assess the diversity and abundance of elasmobranch fishes in coral reef and sand flat environments on the eastern Caicos Bank, with a view to informing marine spatial planning as the island of South Caicos and its environs transition to a tourism-based economy. Using baited remote underwater video systems (BRUVS), the nurse shark Ginglymostoma cirratum, Caribbean reef shark Carcharhinus perezi, spotted eagle ray Aetobatus narinari, southern stingray Hypanus americanus, lemon shark Negaprion brevirostris, tiger shark Galeocerdo cuvier, blacknose shark Carcharhinus acronotus, and great hammerhead shark Sphyrna mokarran were observed to use these waters, with G. cirratum and C. perezi being particularly abundant. Species diversity and overall abundance was greater in the reef environment than on the sand flats, but G. cirratum was equally abundant in both environments. Furthermore, even reef-associated species such as C. perezi were occasionally encountered on the flats a considerable distance from the reef. This indicates that although marine conservation efforts in the Turks and Caicos Islands should continue to focus on coral reef areas, less dramatic environments such as sand flats should not be ignored.
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The species composition of batoid fishes from coastal waters of the Socotra Archipelago is reviewed, with confirmed records of the wedgefish Rhynchobatus djiddensis (Forsskål, 1775) and four new records of sharkrays, wedgefishes, and guitarfishes based on collected specimens, including one species from Abd al-Kuri Island, Rhina ancylostoma Bloch & Schneider, 1801 (Rhinidae), and three species from the main island Socotra, Acroteriobatus salalah (Randall & Compagno, 1995) and Rhinobatos punctifer Compagno & Randall, 1987 (Rhinobatidae), and Rhynchobatus australiae Whitley, 1939 (Rhinidae). Among the new records for the Socotra Archipelago, R. australiae represents the first verified record for the Arabian region. In addition, records of four stingray species (Dasyatidae) are verified based on underwater observations accompanied with photographs. All recorded batoid fishes are commercial species caught in the local small-scale fishery. Information on the identification and distribution of each species is provided.
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The rapid expansion of human activities threatens ocean-wide biodiversity. Numerous marine animal populations have declined, yet it remains unclear whether these trends are symptomatic of a chronic accumulation of global marine extinction risk. We present the first systematic analysis of threat for a globally distributed lineage of 1,041 chondrichthyan fishes-sharks, rays, and chimaeras. We estimate that one-quarter are threatened according to IUCN Red List criteria due to overfishing (targeted and incidental). Large-bodied, shallow-water species are at greatest risk and five out of the seven most threatened families are rays. Overall chondrichthyan extinction risk is substantially higher than for most other vertebrates, and only one-third of species are considered safe. Population depletion has occurred throughout the world's ice-free waters, but is particularly prevalent in the Indo-Pacific Biodiversity Triangle and Mediterranean Sea. Improved management of fisheries and trade is urgently needed to avoid extinctions and promote population recovery.
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The extinction risk of sharks, rays and chimaeras is higher than that for most other vertebrates due to low intrinsic population growth rates of many species and the fishing intensity they face. The Arabian Sea and adjacent waters border some of the most important chondrichthyan fishing and trading nations globally, yet there has been no previous attempt to assess the conservation status of species occurring here. Using IUCN Red List of Threatened Species Categories and Criteria and their guidelines for application at the regional level, we present the first assessment of extinction risk for 153 species of sharks, rays and chimaeras. Results indicate that this region, home to 15% of described chondrichthyans including 30 endemic species, has some of the most threatened chondrichthyan populations in the world. Seventy-eight species (50.9%) were assessed as threatened (Critically Endangered, Endangered or Vulnerable), and 27 species (17.6%) as Near Threatened. Twenty-nine species (19%) were Data Deficient with insufficient information to assess their status. Chondrichthyan populations have significantly declined due to largely uncontrolled and unregulated fisheries combined with habitat degradation. Further, there is limited political will and national and regional capacities to assess, manage, conserve or rebuild stocks. Outside the few deepsea locations that are lightly exploited, the prognosis for the recovery of most species is poor in the near-absence of management. Concerted national and regional management measures are urgently needed to ensure extinctions are avoided, the sustainability of more productive species is secured, and to avoid the continued thinning of the regional food security portfolio.
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Nearshore, shallow water habitats are believed to be highly important for various species of threatened sharks and rays (batoids) around the world. Yet, there is limited information on which batoid species use them. During eldwork on Siniya Island in the Emirate of Umm al-Qaiwain, United Arab Emirates (UAE), rays and guitar sh were observed on twelve occasions in shallow waters or found stranded along the shoreline. At least three species were identi ed from at least 20 individuals (adults and juveniles) consisting of the Arabian banded whipray, Maculabatis randalli, the Halavi guitar sh, Glaucostegus halavi, and cowtail rays, Pastinachus sp. Our observations highlight the importance of shallow water habitats for at least these batoids. Many coastal habitats in the UAE and broader region are currently threatened by development projects and other anthropogenic activities, highlighting the urgent need to better understand their role in maintaining shallow subtidal biodiversity.
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Baited Remote Underwater Video Stations (BRUVS) is a popular technique to assess mobile nektonic and demersal assemblages, particularly for fish communities. The benefits of using BRUVS have been well documented, with their non-destructive and non-extractive nature, ease to replicate, relatively-cheap personnel costs, and low risk to personnel often cited. However, there is a wide variability in the set-up, experimental design, and implementation of this method. We performed a literature review of 161 peer-reviewed studies from all continents published from 1950 to 2016 to describe how BRUVS has been used by quantitatively assessing 24 variables, including camera set-up and orientation, soak time, bait quantity, type and preparation method, habitat and depth deployed in, and number of replicates used. Such information is critical to gauge the comparability of the results obtained across BRUVS studies. Generally, there was a wide variety in the location, deployment method, bait used, and for the purpose that BRUVS was deployed. In some studies, the methods were adequately described so that they included information on the 24 variables analysed, but there were 34 % of studies which failed to report three or more variables. We present a protocol for what minimal information to include in methods sections and urge authors to include all relevant information to ensure replicability and allow adequate comparisons to be made across studies.
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Fisheries are complex social-ecological systems, where managers struggle to balance the socio-economic interests of fishing communities with the biology and ecology of fisheries species. Spatial closures are a popular measure to address conservation and fisheries management goals, including the protection of shark populations. However, very little research has been published on the effectiveness of shark-specific closures to protect sharks, or their impacts on fisher behavior. Situated within the global center of tropical marine biodiversity, Indonesia’s shark fishery contributes more to the international shark fin trade than any other nation. Here we evaluate the effect of shark-specific closures on sharks and other species of interest, as well as shark fishers’ responses to losing access to their former fishing grounds. We assessed shark diversity and abundance in an open access zone (OAZ) and two No-Take Zones (NTZs) of a Marine Protected Area within the recently established shark sanctuary in Raja Ampat, Indonesia, where sharks have high monetary value as a tourism attraction. Shark abundance was significantly higher in the privately managed NTZs than in the OAZ. Across all management zones, neither zone size, depth nor reef complexity explained variations in shark abundance, suggesting that governance is the main driver of successful shark conservation areas. These trends were also reflected in species targeted by small-scale reef fisheries, including snappers, emperor, groupers, tunas, mackerels, and large-bodied wrasse and parrotfish. Interviews with shark fishers who lost access to their primary fishing grounds when the shark sanctuary was established showed that while most fishers (88%) knew that sharks were protected in Raja Ampat, many were unsure about the purpose of the sanctuary. Few fishers felt that the agencies implementing fishing bans understood their livelihood needs. We found that shark fishers adapted to the loss of former fishing grounds by shifting fishing effort to other locations or diversifying their livelihoods, including illegal petrol transport. While conserving sharks for tourism can be effective, it may inadvertently result in displacing fishing effort to unprotected regions. We propose that effective shark conservation in Indonesia will need to combine strategic spatial protection with efforts to support livelihood security and diversification.
Shark-like batoids (Rhinopristiformes) represent of some of the most threatened families of sharks and rays. In certain regions, they are a relatively important component of elasmobranch fisheries, commonly taken as by-catch in gillnets and longlines, but also increasingly targeted for their high value fins and meat. This demand, combined with intense fishing pressure, has resulted in global population declines as well as localized extinctions of many rhinopristoids. Yet, information on the life-history, ecology, and conservation status remains scarce for most species. From 2010-2012, data was opportunistically collected from thirteen rhinopristoid species, including four endemic to the Arabian Sea and adjacent waters, landed from fisheries in the United Arab Emirates or transported from Oman. Four taxa dominated and comprised 92% of total shark-like batoid landings by number, namely Rhynchobatus spp., the Halavi guitarfish (Glaucostegus halavi), bowmouth guitarfish (Rhina ancylostoma), and Bengal guitarfish (Rhinobatos annandalei). Details of the biological characteristics, including size composition and sex ratios, are presented for each species. While there remain identification challenges related to some unresolved taxonomic issues, with several likely undescribed species occurring in the region, the first regional checklist of rhinopristoids is provided. Evidence of significant declines in landings combined with increasing fishing effort over a short time period raises concern about the status and long-term persistence of many species. Increased research to understand the biology, ecology, diversity, and resilience to harvest by fisheries is critical to the effective management of these species and an urgent precautionary approach to their conservation is warranted.
Video surveys are an essential tool for monitoring marine communities. Their use to study elasmobranch populations has dramatically increased over the last decade. However, the restricted field-of-view (FOV) of traditional cameras in these surveys may bias abundance estimates in a number of ways, including saturation at high densities and low detection probability for rare or cryptic species. This study investigated these potential biases using newly developed full-spherical (FS) camera technology. A comparison of 35 Baited Remote Underwater Video surveys (BRUVs), using both FS and traditional cameras, was conducted from July to August 2016 in shallow waters (0.4 to 8.5 m) of Tetiaroa, French Polynesia. Both blacktip reef Carcharhinus melanopterus and sicklefin lemon sharks Negaprion acutidens were quantified from traditional cameras using MaxN and MeanCount methods. These estimates were then regressed against FS cameras counts, which were assumed to more accurately represent site abundance, to test for gear saturation. Detection probabilities of the traditional and FS cameras were assessed using a Bayesian binomial model, with uninformed-uniform priors. Results indicated a significant effect of gear saturation for standard BRUVs as counts on FS cameras increased, regardless of the metric used. Furthermore, traditional cameras had a significantly lower detection probability (mean ± 2 SD: 69.88 ± 0.008%) than FS cameras (81.20 ± 0.007%). Our findings show that traditional cameras are unlikely to adequately discriminate differences in shark relative abundance at high densities. Therefore, standard BRUV techniques that use restricted FOV cameras are likely limited in their ability to provide accurate information to managers once populations have reached particular thresholds of abundance.
The Arabian Seas Region plays an important role in the global landings and trade of sharks and rays. The United Arab Emirates (UAE) and Yemen, two countries with stark socioeconomic differences, serve as major regional trade hubs for shark and ray products and four countries (Oman, Pakistan, UAE and Yemen) supply nearly 11% of dried fin exports to Hong Kong. Yet, little information is available on the characteristics of this trade and the fisheries contributing to it. Here, we review the fisheries characteristics , trade, utilization and distribution chain of sharks and rays in 15 countries of the Arabian Seas Region based on published and grey literature, landing surveys, field observations and interviews with fishermen and traders. Although regional shark fisheries remain mostly artisanal, reported shark and ray landings represent 28% of the regional total fish production, reaching 56,074 mt in 2012 (7.3% of total world catches), with Iran, Oman, Pakistan and Yemen ranking as the primary catchers. Utilization and distribution patterns are complex, vary between landing sites and countries, and remain unmonitored. Based on widespread over-exploitation of most teleost fisheries, current exploitation levels for most sharks and rays are potentially unsustainable. The situation is exacerbated by limited research and political will to support policy development, the incomplete nature of fisheries data, as well as insufficient regulations and enforcement. A better understanding of shark and ray fisheries will be key for regulating trade, promoting conservation and developing management initiatives to secure food security, livelihoods and biodiversity conservation in the region. K E Y W O R D S chondrichthyans, conservation, extinction risk, fin trade, fisheries management, sustainability