Remote Underwater Video Research Articles

A baited remote underwater video system (BRUVS) assessment of elasmobranch diversity and abundance on the eastern Caicos Bank (Turks and Caicos Islands); an environment in transition

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.

Submerged Carbonate Banks Aggregate Pelagic Megafauna in Offshore Tropical Australia

The conservation of marine biodiversity is firmly embedded in national and international policy frameworks. However, the difficulties associated with conducting broad-scale surveys of oceanic environments restrict the evidence base available for applied management in pelagic waters. For example, the Oceanic Shoals Australian Marine Park (AMP) was established in 2012 in a part of Australia’s continental shelf where unique topographic features are thought to support significant levels of biodiversity, yet where our understanding of ecological processes remains limited. We deployed midwater baited remote underwater video systems (midwater BRUVs) in the Oceanic Shoals AMP to provide the first non-extractive baseline assessment of pelagic wildlife communities in the area. We used these observations and high-resolution multibeam swaths of the seafloor to explore potential relationships between prominent geomorphological features and the (i) composition, (ii) richness, and (iii) total abundance of pelagic communities. We documented 32 vertebrate species across three sampling areas, ranging from small baitfish to large sharks and rays, and estimated that up to twice as many taxa may occur within the region as a whole. This highlights the Oceanic Shoals AMP as a reservoir of biodiversity comparable to other documented offshore oceanic hotspots. Our results also confirm the AMP as a possible distant foraging destination for IUCN red listed sea turtles, and a potential breeding and/or nursing ground for a number of charismatic cetaceans. Model outputs indicate that both species richness and abundance increase in proximity to raised geomorphic structures such as submerged banks and pinnacles, highlighting the influence of submarine topography on megafauna distribution. By providing a foundational understanding of spatial patterns in pelagic wildlife communities throughout a little studied region, our work demonstrates how a combination of non-destructive sampling techniques and predictive models can provide new opportunities to support decision-making under data shortage.

The macroecology of reef fish agonistic behaviour

Understanding the interplay between processes operating at large and small spatiotemporal scales in shaping biotic interactions remains challenging. Recent studies illustrate how phenotypic specialization, species life‐history traits and/or resource partitioning recurrently underlie the structure of mutualistic interactions in terrestrial ecosystems along large latitudinal gradients of biodiversity. However, we know considerably less about how local processes interact with large‐scale patterns of biodiversity in modulating biotic interactions in the marine realm. Considering agonistic behaviour as a proxy for contest competition, we empirically investigate whether the structure of reef fish agonistic interactions is conserved across a 34 000‐km longitudinal gradient of biodiversity. By sampling coral reefs using standardized remote underwater video, we found recurrent patterns of fish agonistic behaviour in disparate communities distributed across five biogeographic provinces of the Pacific and Atlantic oceans. While the sheer number of species increases with regional richness, the number of aggressive disputes at the habitat scale is similar across communities. We then combined generalized linear models and network theory to reveal that, the emergent structure of local agonistic networks is not modular but instead recurrently display a nested structure, with a core of highly interactive site‐attached herbivores of the Pomacentridae family. Therefore, despite the increase in the number of species involved in agonistic interactions toward speciose communities, the network structure is conserved along the longitudinal richness gradient because local disputes are mostly driven by closely‐related, functionally‐similar species. These findings suggest that evolutionary and local processes interact in modulating reef fish agonistic behaviour and that fine‐scale niche‐partitioning can structure the ecological networks in marine ecosystems.

Comparison of Artificial and Natural Reef Productivity in Nantucket Sound, MA, USA

Artificial reef communities undergo long periods of succession prior to becoming stable, but funding challenges often prevent post-deployment monitoring from evaluating long-term successional changes. The present study employed baited remote underwater video surveillance (BRUVS) to compare the species richness, diversity, abundance, and age structure of fishes across a 4-year-old artificial reef, a 41-year-old artificial reef, a representative natural reef, and a bare control in Nantucket Sound, MA, USA, to address whether the perceived success of an artificial reef can be determined 5 years after deployment. Results indicated that, while species richness and diversity were largely uniform throughout the Sound, fish appeared on camera 93.4% faster at artificial reef sites than they did at the bare sand control. Reef-associated fish were 103.7% more abundant on the older artificial reef than on the younger artificial reef. Therefore, although the younger artificial reef is in its fifth year of monitoring, abundances of economically important fishes on the reef may continue to increase in future years and current numbers may not accurately reflect reef success or failure. Future management plans should consider extending monitoring programs longer than 5 years and implementing temporal fishing closures on newly deployed reefs to facilitate earlier post-deployment community stabilization.

Optimal soak times for Baited Remote Underwater Video Station surveys of reef-associated elasmobranchs.

Effective sampling of marine communities is essential to provide robust estimates of species richness and abundance. Baited Remote Underwater Video Stations (BRUVS) are a useful tool in assessment of fish assemblages, but research on the optimal sampling period required to record common and rare elasmobranch species is limited. An appropriate ‘soak time’ (time elapsed between settlement of the BRUVS on the seabed and when it is hauled off the seabed) requires consideration, since longer soak times may be required to record species rare in occurrence, or sightings in areas of generally low elasmobranch abundance. We analysed 5352 BRUVS deployments with a range of soak times across 21 countries in the Coral Triangle and Pacific Ocean, to determine the optimal soak time required for sampling reef-associated elasmobranchs, considering species rarity, and community abundance at each site. Species were categorised into 4 ‘rarity’ groups (very rare to common), by their relative occurrence in the dataset, defined simply by the proportion of BRUVS on which they occurred. Individual BRUVS were categorised into 3 ‘abundance’ groups (low to high) by overall relative elasmobranch abundance, defined as total number of all elasmobranchs sighted per unit of sampling effort. The effects of BRUVS soak times, and levels of rarity and abundance groupings, on the time to first sighting (TFS) and time to maximum number of elasmobranchs observed (tMaxN) were examined. We found that TFS occurred earlier for species groups with high occurrence, and on BRUVS with high elasmobranch abundance, yet longer soak times were not essential to observe rarer species. Our models indicated an optimum of 95% of both sighting event types (TFS, tMaxN) was recorded within 63–77 minutes, and a soak time of 60 minutes recorded 78–94% of the elasmobranch sighting events recorded (78–94% of TFS events and 82–90% of tMaxN events), when species rarity and abundance on BRUVS was accounted for. Our study shows that deployments of ~ 77 minutes are optimal for recording all species we observed, although 60 minutes soak time effectively samples the majority of elasmobranch species in shallow coral reef habitats using BRUVS.

When sharks are away, rays will play: effects of top predator removal in coral reef ecosystems

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.

Accounting for spatial scale and temporal variation in fish-habitat analyses using baited remote underwater video stations (BRUVS)

With the implementation of marine spatial planning in many coastal regions of the world, there is a need to understand how marine species and communities respond to environmental heterogeneity. Predictive modelling approaches are one efficient method for associating marine communities with variations across the seascape. These approaches, along with increasing access to spatially explicit environmental data, provide improved opportunities for modelling fish assemblages. Baited remote underwater video stations (BRUVS) are a popular means of gathering fish assemblage data in the coastal zone, but have biases in bait attraction, trophic groups sampled, and behavioral conditions. To account for these biases, spatial and temporal scales of analyses must be considered. In this study, we combined time-series BRUVS observations with seafloor and oceanographic variables in generalized additive models to model patterns of relative species richness and abundance in temperate coastal fish assemblages across multiple habitat types, functional trophic groups, and spatial scales from 5-500 m. We show that the spatial and temporal scale of analyses and behavioral characteristics of target species (such as mobility) are important considerations when predicting the spatial distribution of a particular assemblage or functional subset. The resulting models performed well, with prediction accuracies up to 79% while explaining between 24 and 83% of variance. These models were then used to extrapolate assemblage characteristics over broader areas of the seafloor to expand our understanding of fish distributions, providing valuable insights for marine spatial planning, including marine protected area assessment.

The MacKinnon Lists Technique: An efficient new method for rapidly assessing biodiversity and species abundance ranks in the marine environment.

Widespread and ever-increasing anthropogenic impacts in the marine environment are driving a need to develop more efficient survey methods for monitoring changes in marine biodiversity. There is a particular urgent need for survey methods that could more rapidly and effectively detect change in species richness, abundance and community composition. Here, test the suitability of the Mackinnon Lists Technique for use in the marine environment by testing its effectiveness for rapid assessment of fish communities. The MacKinnon Lists Technique is a time-efficient and cost-effective sampling method developed for studying avian tropical biodiversity, in which several list samples of species can be collected from a single survey. Using the well-established MaxN approach on data from deployments of a Baited Remote Underwater Video Systems for comparison, we tested the suitability of the MacKinnon Lists Technique for use in marine environments by analysing tropical reef fish communities. Using both methods for each data set, differences in community composition between depths and levels of protection were assessed. Both methods were comparable for diversity and evenness indices with similar ranks for species. Multivariate analysis showed that the MacKinnon Lists Technique and MaxN detected similar differences in community composition at different depths and protection status. However, the MacKinnon Lists Technique detected significant differences between factors when fewer videos (representing reduced survey effort) were used. We conclude that the MacKinnon Lists Technique is at least as effective as the widely used MaxN method for detecting differences between communities in the marine environment and suggest can do so with lower survey effort. The MacKinnon Lists Technique has the potential to be widely used as an effective new tool for rapid conservation monitoring in marine ecosystems.

Tropical intertidal seagrass beds: An overlooked foraging habitat for fishes revealed by underwater videos

Intertidal seagrass beds occur throughout the tropical Indo-Pacific region and several studies have shown that small fishes inhabit them when inundated during the tidal regime. However, there is a lack of evidence regarding the trophic importance of these habitats to different fish populations at such times. In this study, we examined the feeding behavior of the juvenile fish communities during an incoming tide at two intertidal seagrass bed sites in northern Mindanao, Philippines, during both wet and dry seasons, by deploying remote underwater video cameras. The video footages (3 h) revealed that nearly half of all fish species arrived within 30 min from the start of recording (ca. 30–40 cm water depth, 10–20 cm above the seagrass canopy), and that species richness gradually increased with rising tide, reaching 80% of recorded species within 120 min at both sites in both seasons. Small juvenile (<10 cm total length) labrids, lethrinids, lutjanids, and siganids were most abundant in all video recordings. Large juveniles (>10 cm total length) of the latter three families were first to invade intertidal seagrass beds with incoming tides, whereas those of Labridae were more abundant in later stages of the tidal cycle. The fishery target families Labridae, Lethrinidae, Siganidae, and Lutjanidae foraged during the rising tide, pointing to the importance of intertidal seagrass beds as a foraging habitat for at least 17 species. Because these habitats are disappearing due to expanding coastal developments for human use, the results highlight the ecological importance as a foraging area for multiple fish species to which it may help support developing conservation and management policies in coastal zones.

A Time-Extended (24 h) Baited Remote Underwater Video (BRUV) for Monitoring Pelagic and Nocturnal Marine Species

Baited remote underwater video systems (BRUVs) are efficient devices for remotely characterising the assemblage and relative density of fishes and other marine organisms. However, technological constraints (e.g., battery life and limited storage memory) typically limit deployment times to &lt;2 h making it very difficult to capture the presence of marine species, including rare and elusive ones. We developed an extended duration (24 h) BRUV to enable fisheries-independent surveying of a pelagic shark population in the western Mediterranean. Video data revealed seven visits (three nocturnal, four diurnal) by blue sharks (Prionace glauca) over a period of 1355 h. In the future, this cost-effective device could be fitted with a wireless video transmitter to provide real-time observations of marine animals for scientific or ecotourism purposes.

Effects of exposure to large sharks on the abundance and behavior of mobile prey fishes along a temperate coastal gradient.

Top predators can exert strong influences on community structure and function, both via direct, consumptive effects, as well as through non-consumptive, fear-based effects (i.e. predation risk). However, these effects are challenging to quantify, particularly for mobile predators in marine ecosystems. To advance this field of research, here we used baited remote underwater video stations (BRUVs) to assess how the behavior of mobile fish species off Cape Cod, Massachusetts, was affected by exposure to large sharks. We categorized sites into three levels of differential shark predation exposure (white sharks, Carcharodon carcharias) and quantified the relative abundance and arrival times (elapsed time before appearing on screen) for six mobile fish prey groups to the BRUV stations. Increased large shark exposure was associated with a decrease in overall prey abundance, but the overall response was prey group-specific. Foraging of smooth dogfish, a likely important prey item for large sharks in the system, was significantly reduced in areas frequented by white sharks. Specifically, the predicted probabilities of smooth dogfish bait contacts or bite attempts occurring were reduced by factors of 5.7 and 8.4, respectively, in areas of high exposure as compared to low exposure. These modifications were underscored by a decrease in smooth dogfish abundance in areas of high exposure as well. Our results suggest that populations of large, roving sharks may induce food-related costs in prey. We discuss the implications of this work within the context of the control of risk (COR) hypothesis, for the purposes of advancing our understanding of the ecological role and effects of large sharks on coastal marine ecosystems.

Seascape connectivity exerts differing effects for fish assemblages in distinct habitats of the surf zones of ocean beaches

Abstract Animals move throughout coastal seascapes to disperse, feed, and spawn, including the surf zones of ocean beaches. Yet, the influences of seascape context on surf-zone fish are largely unquantified. We sampled surf-zone fish assemblages with baited remote underwater video deployments at 25 beaches across 50 km of coastline in eastern Australia to determine if variation in the spatial configuration of broader coastal seascapes shapes fish assemblages in different surf-zone habitats. We show that surf zones are not homogenous fish habitats, with offshore bars and nearshore troughs having distinct fish assemblages, shaped by different environmental variables. Fish assemblages of offshore bars were characterized by greater species richness and a higher abundance of indicator species (as identified by Dufrene–Legendre indicator species analysis) when close to rocky reefs and estuaries. In contrast, fish assemblages of nearshore troughs were characterized by greater species richness and a higher abundance of indicator species when far from estuaries, and off wider beaches. Our results highlight the importance of seascape connectivity in structuring surf-zone fish assemblages. Consequently, management approaches need to more thoroughly quantify the effects of seascape connectivity over smaller spatial scales and consider surf zones as key components of broader coastal habitat mosaics.

Comparing methodologies in marine habitat monitoring research: An assessment of species-habitat relationships as revealed by baited and unbaited remote underwater video systems

Remote underwater video systems (RUVS) are increasingly used in scientific studies to monitor marine ecosystems. RUVS can be deployed baited (BRUVS) or unbaited (UBRUVS) and allow for an estimation of the MaxN metric, a relative measure of species abundance. Recording species MaxN in a variety of marine habitats provides associations between species abundance and habitat type, known as ‘species-habitat relationships’. However, the introduction of bait in BRUVS could obscure such relationships by inadvertently attracting fish from neighbouring habitats. Here, we investigate the species-habitat relationships of seven temperate marine species: Atlantic cod (Gadus morhua), right-eyed flatfish (Pleuronectinae spp.), Atlantic herring (Clupea harengus), whiting (Merlangius merlangus), goldsinny wrasse (Ctenolabrus rupestris), two-spotted goby (Gobiusculus flavescens) and shore crab (Carcinus maenas) as revealed by BRUVS and UBRUVS. Video systems were deployed in coastal areas in the Western Baltic, with a cobble coverage ranging from 0% to 100%. Results show that all focal species responded to changes in cobble coverage, highlighting the importance of benthic habitat for a range of animals including benthopelagic species. Specifically, mean abundances of goldsinny wrasse and two-spotted goby were positively associated with cobble coverage, whilst right-eyed flatfish, herring, whiting and shore crab showed a negative association. Atlantic cod was found to be most abundant at intermediate cobble coverage between 65 and 70%, showing a unimodal trend with the mean abundance decreasing again at higher coverage. The relationships suggest that anthropogenic activities modifying benthic habitats, including extraction of material from the seabed and bottom trawling, likely change abundances of a range of marine species. Our comparative analysis suggests that both BRUVS and UBRUVS can identify previously documented species-habitat relationships. However, BRUVS demonstrated some superiority by confirming documented relationships for Atlantic cod and whiting, whilst UBRUVS failed to record any patterns for those species. Our data highlight the ability of BRUVS to identify changes in abundance across different habitats for a variety of species. Although the bait plume serves to attract organisms to the field of view, current results suggest that the use of BRUVS does not obscure species-habitat relationships in patchy coastal habitats. Therefore, future studies examining the importance of different marine areas may benefit from using BRUVS to quantify relationships between habitat variables and species abundance. Developing a better understanding of such relationships will be crucial in ensuring adequate management and protection of ecologically important marine habitats.

Dermal denticle assemblages in coral reef sediments correlate with conventional shark surveys

Abstract It is challenging to assess long‐term trends in mobile, long‐lived and relatively rare species such as sharks. Despite ongoing declines in many coastal shark populations, conventional surveys might be too fleeting and too recent to describe population trends over decades to millennia. Placing recent shark declines into historical context should improve management efforts as well as our understanding of past ecosystem dynamics. A new palaeoecological approach for surveying shark abundance on coral reefs is to quantify dermal denticle assemblages preserved in sediments. This approach assumes that denticle accumulation rates correlate with shark abundances. Here, we test this assumption by comparing the denticle record in surface sediments to three conventional shark survey methods at Palmyra Atoll, Line Islands, central Pacific Ocean, where shark density is high and spatially heterogeneous. We generally found a significant positive correlation between denticle accumulation rates and shark abundances derived from underwater visual census, baited remote underwater video and hook and line surveys. Denticle accumulation rates reflected shark abundances, suggesting that denticle assemblages can preserve a signal of time‐averaged shark abundance in low‐energy coral reef environments. We offer suggestions for applying this tool to measure shark abundance over long time‐scales in other contexts.

Benthic Habitats, as Derived from Classification of Side‐Scan‐Sonar Mapping Data, Are Important Determinants of Reef‐Fish Assemblage Structure in the Eastern Gulf of Mexico

AbstractIncreasingly restrictive management regulations have greatly reduced the utility of fishery‐dependent data for characterizing temporal changes in the abundance of managed fish populations, so fishery‐independent data are becoming more important for the accurate assessment of stock status. A notable downside to fishery‐independent data is the high cost of conducting surveys, and efforts to maximize survey efficiency are critical given ongoing reductions in agency funding. We conducted a pilot study to explore the utility of classifying side‐scan‐sonar mapping data to provide a practical a priori characterization of reef habitat in the eastern Gulf of Mexico. An analysis of side‐scan‐sonar mapping data identified five distinct reef habitat types (low‐relief hard bottom, mixed hard bottom, fragmented hard bottom, ledges, and potholes) that were subsequently sampled with stereo baited remote underwater video (S‐BRUV) arrays and trap‐mounted GoPro cameras. The permutational analysis of variance indicated that the assemblage structure of reef fish differed significantly (P &lt; 0.01) among all of the pairs of habitats except ledges and fragmented hard bottom; assemblage structure did not differ among cameras (P = 0.45). Overall species richness and diversity were significantly higher in the habitats with greater vertical relief, as were the abundances of several economically and ecologically important reef fishes, although many taxa were observed across all of the habitat types. Benthic habitats that are identified from side‐scan‐sonar mapping data are important determinants of reef‐fish assemblage structure and may prove to be useful as a stratification scheme for reef‐fish surveys, although additional research is necessary to explore the transferability of these results to the rest of the eastern Gulf of Mexico.

Individual and Population Benefits of Marine Reserves for Reef Sharks.

No-take marine protected areas (MPAs) are a commonly applied tool to reduce human fishing impacts on marine and coastal ecosystems. However, conservation outcomes of MPAs for mobile and long-lived predators such as sharks are highly variable. Here, we use empirical animal tracking data from 459 individual sharks and baited remote underwater video surveys undertaken in 36 countries to construct an empirically supported individual-based model that estimates the conservation effectiveness of MPAs for five species of coral reef-associated sharks (Triaenodon obesus, Carcharhinus melanopterus, Carcharhinus amblyrhynchos, Carcharhinus perezi, and Ginglymostoma cirratum). We demonstrate how species-specific individual movement traits can contribute to fishing mortality of sharks found within MPAs as they move outside to adjacent fishing grounds. We discovered that the world's officially recorded coral reef-based managed areas (with a median width of 9.4 km) would need to be enforced as strict no-take MPAs and up to 5 times larger to expect protection of the majority of individuals of the five investigated reef shark species. The magnitude of this effect depended on local abundances and fishing pressure, with MPAs required to be 1.6-2.6 times larger to protect the same number of Atlantic and Caribbean species, which occur at lower abundances than similar species in the western Pacific. Furthermore, our model was used to quantify partially substantial reductions (>50%) in fishing mortality resulting from small increases in MPA size, allowing us to bridge a critical gap between traditional conservation planning and fisheries management. Overall, our results highlight the challenge of relying on abundance data alone to ensure that estimates of shark conservation impacts of MPAs follow the precautionary approach.

The importance of oceanic atoll lagoons for coral reef predators

Predators on coral reefs play an important ecological role structuring reef fish communities and are important fishery targets. It is thought that reef predator assemblages increase in density and diversity from inner lagoonal to outer edge reefs. Oceanic atolls may differ though, as nutrients are available throughout. Reef predator populations are declining, but there is little known about how their distributions may vary across oceanic atolls. Using a combination of underwater visual census and baited remote underwater video, this study aimed to compare reef predator populations between inner and outer reefs of North Malé Atoll (Maldives) and determine which reef metrics may drive any differences in assemblage structure. We found that predator assemblages were significantly different between inner and outer atoll. Body sizes of several predator families were consistently larger in the outer atoll, however, abundance, biomass and species richness were similar between outer edge reefs and inner lagoonal reefs suggesting atoll lagoons may be undervalued habitats. Depth and complexity were consistently important predictors of the predator assemblage. Inner atoll lagoonal habitat is equally as important for reef predator assemblages as outer reef slopes, although the dominant species differ. This study provides important information on reef predator populations in the Maldives, where detailed assessments of the reef predator assemblage are lacking but the reef fishery is thriving and annual catch will continue to increase.

Assessment of faunal communities and habitat use within a shallow water system using non-invasive BRUVs methodology

Seagrass and mangrove habitats have long been established as critical for diverse species at various life-stages, particularly as nursery grounds. However, despite their intrinsic and environmental value, these ecosystems are increasingly threatened by anthropogenic activities. In Bimini, Bahamas, where ongoing development threatens ecosystem integrity, baited remote underwater video surveys (BRUVs) were used to examine faunal communities in both nearshore habitat and a shallow water central lagoon (average depth 1 m). The study assessed species abundances and spatial distribution in a currently unperturbed of the North Bimini Marine Reserve (NBMR).A total of 140 BRUVs, conducted over a 13-month period, recorded 62 species from 27 different families. MaxN was used to assess relative abundances and multivariate analyses (i.e. nMDS, PCA, PERMANOVA) investigated differences in community composition across discrete factors and environmental variables. Boosted Regression Trees (BRTs) were used to explore environmental variables for their uncorrelated influences on recorded species diversity. Findings evidenced the importance of habitat diversity and particularly mangrove-adjacent habitat for teleost fishes in Bimini with species diversity and abundance being significantly greater in the mangrove-adjacentdge habitat. Further, the study highlighted differences in environmental conditions between habitat types and the association this had with species diversity, abundance and distribution. Despite the shallow water environment, BRUVs served as a scalable, non-invasive technique to assess community structures within the study site. Results from this study should inform ongoing decision-making processes regarding the protection of the Bimini Islands ecosystem.

Chondrichthyans as an umbrella species-complex for conserving South African biodiversity

Conservation surrogates, such as umbrella and flagship species, could help focus South Africa’s limited resources for research and management and enhance the conservation gains from marine protected areas (MPAs). Sharks, rays and chimaeras (Chondrichthyes), which are charismatic and ecologically diverse, are potential umbrella candidates, but tests of the ecological suitability of putative marine umbrella species are lacking. Using baited remote underwater video in and around two MPAs in the Western Cape Province, we assessed the potential of chondrichthyans as an umbrella species-complex by quantifying the relationships and co-occurrence patterns between chondrichthyan abundance and diversity and those of other taxa (primarily teleosts and crustaceans). Sites with abundant chondrichthyans, with catsharks or large sharks (>1 m total length), all had significantly greater abundance and diversity of these other taxa, and associations with species of commercial and conservation interest (e.g. roman Chrysoblephus laticeps). Endemic scyliorhinids (notably dark catshark Haploblepharus pictus) and the broadnose sevengill shark Notorynchus cepedianus also had many strong positive co-occurrences (28% and 21% of interactions, respectively). The puffadder catshark H. edwardsii had the highest centrality of any species, denoting its high connectedness to other taxa. Overall, chondrichthyans, especially the dark and puffadder catsharks and the broadnose sevengill shark, show strong potential as an umbrella species-complex in South Africa.

Contrasting patterns in the abundance of fish communities targeted by fishers on two coral reefs in southern Mozambique

Coastal populations of maritime countries in eastern Africa rely on fish as a primary source of protein, but baseline information on the abundance of fish communities on these coastlines is often lacking. We used baited remote underwater video stations to compare the abundance and diversity of reef fishes targeted by fishing at two sites in southern Mozambique, one at Lighthouse Reef within the Bazaruto Archipelago National Park and the other to the south at San Sebastian Reef on the San Sebastian Peninsula. Fish that are known targets of fisheries (mostly small-scale and artisanal) had an abundance that was almost three-times greater at San Sebastian Reef (80.22 ind. h–1 [SE 18.00]) than at Lighthouse Reef (29.70 ind. h–1 [SE 8.91]). Similarly, there was greater mean species richness at San Sebastian Reef (38.74 species h–1 [SE 2.79]) than at Lighthouse Reef (25.37 species h–1 [SE 3.66]). The main drivers of targeted fish abundance were habitat and depth, with shallow (<15 m) and mixed reef areas having the greatest abundance and richness. More sampling was done over sand habitat at Lighthouse Reef, which likely led to the lower abundance and species richness observed at this site; however, that finding could also be attributable to the fact that protection is provided to only a section of available coral reef habitat in a small area. Nevertheless, fish community structure was comparable between the sites, with similar proportions of carnivores (78–81%), herbivores (12–14%) and omnivores (7–8%). Our findings highlight the variation in species abundance and assemblages of coral-reef fish targeted by fishing in Mozambique and emphasise the importance of localised environmental variables as a driver of these patterns. To ensure maximum protection of Lighthouse Reef fish communities, we recommend an extension of the no-take zone to include the entire reef complex.