ISRA FACTSHEETS
ISRA FACTSHEETS
WESTERN INDIAN OCEAN REGION
Greater Bazaruto
Summary
Greater Bazaruto is located on the northern coast of Mozambique’s Inhambane Province in the southwest of the Mozambique Channel. The area encompasses an archipelago of five islands (Bazaruto Archipelago) and a diversity of coastal and benthic habitats including subtropical rocky reefs, coral reefs, tidal sand flats, seagrass beds, estuaries, and mangrove ecosystems. The area overlaps with two Ecologically or Biologically Significant Marine Areas, the Greater Bazaruto Key Biodiversity Area, the Bazaruto Archipelago National Park, and the Vilanculos Coastal Wildlife Sanctuary. Within this area there are: threatened species (e.g., Bull Shark Carcharhinus leucas); range-restricted species (Greyspot Guitarfish Acroteriobatus leucospilus); feeding areas (Reef Manta Ray Mobula alfredi); resting areas (Bottlenose Wedgefish Rhynchobatus australiae); undefined aggregations (e.g., Scalloped Hammerhead Sphyrna lewini); and areas with distinctive attributes (e.g., Smalleye Stingray Megatrygon microps).
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Greater Bazaruto
DESCRIPTION OF HABITAT
Greater Bazaruto is located along the southern coast of Mozambique in the Western Indian Ocean. This area includes an archipelago of five islands (Bazaruto Archipelago) and the San Sebastian Peninsula. The leeward side of the archipelago is characterised by extensive and dynamic tidal sand flats, with interspersed seagrass beds, coral and rocky reefs, and coastal mangrove ecosystems (Bandeira et al. 2008). The San Sebastian Peninsula includes a range of habitats including coastal dunes, mangroves, and estuaries. The seaward side is characterised by pelagic waters with shallow (8–15 m) coral reefs along the island and underlying subtropical rocky reefs (20–40 m) extending parallel to shore surrounded by sandy substrate (Venables et al. 2022). The continental shelf is narrow with a steep slope, leading to shelf-edge upwelling that increases plankton biomass and creates large prey aggregation areas for filter feeders (Vinayachandran et al. 2021). Mesoscale cyclonic/anticyclonic eddies move southward through the Mozambican Channel, driving frequent and pronounced coastal upwelling in the area (Roberts et al. 2014).
The area overlaps with two protected areas: the Bazaruto Archipelago National Park and the Vilanculos Coastal Wildlife Sanctuary. It also overlaps with two Ecologically or Biologically Significant Marine Area (EBSAs; Save River to San Sebastian and Mozambique Channel; CBD 2023a, 2023b) and with the Greater Bazaruto Key Biodiversity Area (KBA 2023).
This Important Shark and Ray Area is benthopelagic and extends from inshore and surface waters (0 m) to 300 m based on the bathymetry of the area.
CRITERION A
VULNERABILITY
Twelve Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened SpeciesTM regularly occur in the area. Threatened sharks comprise one Critically Endangered species, one Endangered species, and one Vulnerable species; threatened rays comprise one Critically Endangered species, five Endangered species, and three Vulnerable species (IUCN 2023).
CRITERION B
RANGE RESTRICTED
This area holds the regular presence of the Greyspot Guitarfish as a resident range-restricted species. Greyspot Guitarfish are sighted in shallow sandy habitats throughout the area, particularly on the leeward side of the Bazaruto Archipelago. Opportunistic visits to local fish markets and landing sites on the mainland coast of the area (~10–15 times per year during 2018–2023) found this to be among the most frequently landed species of shark or ray (A Marshall & J Conradie pers. obs. 2023). Greyspot Guitarfish only occur in the Agulhas Current Large Marine Ecosystem.
CRITERION C
SUB-CRITERION C2 – FEEDING AREAS
Greater Bazaruto is an important feeding area for one ray species.
Aerial surveys conducted between 2012–2014 (n = 9) recorded 183 Reef Manta Ray sightings in the area, and feeding was observed in almost all (96%) sightings (Marine Megafauna Foundation unpubl. data 2023). On four occasions, large groups (15, 25, 40, and 80 individuals) were actively surface and sub-surface feeding. This species was also observed surface or sub-surface feeding during boat-based surveys every year (2013–2022), albeit in smaller groups (1–5 individuals) than recorded in aerial surveys (Marine Megafauna Foundation unpubl. data 2023). This feeding behaviour is likely to be associated with the frequent and intense upwelling events occurring in the area year-round and supporting high productivity on the shelf (Roberts et al. 2014).
CRITERION C
SUB-CRITERION C3 – RESTING AREAS
Greater Bazaruto is an important resting area for one ray species.
Dive surveys have recorded 262 sightings of Bottlenose Wedgefish in this area, with sightings every year from 2013–2023 (Marine Megafauna Foundation unpubl. data 2023). Few sightings (n = 35) were recorded between 2013–2019. After 2020, when dedicated survey effort began for this species, a mean of 57 sightings per year were recorded (range 46–80 sightings per year). In 60% of sightings for which behaviour was recorded (n = 129), the species was resting in sandy substrate. Resting behaviour was observed at two main sites, one of which is a shallow (<8 m) tidal estuary mouth where they rest around low and high tide, when the current is weakest. Groups of up to 30 individuals have been observed resting and regular sightings of 4–10 individuals have been recorded during drone and snorkel surveys at this site. Resting is also observed on sand flats adjacent to a rocky reef that acts as a cleaning station for the species. Here, individuals rest in groups of up to seven individuals ~20 m away from the specific cleaning area. Bottlenose Wedgefish have not been observed resting at or near the other cleaning station sites in the area, where they are actively cleaning or swimming over the reef. A photo-identification study has identified >80 individuals, with a re-sighting rate of 20%, and shows evidence of individuals moving between resting sites and cleaning stations in the area (Marine Megafauna Foundation unpubl. data 2023).
CRITERION C
SUB-CRITERION C5 – UNDEFINED AGGREGATIONS
Greater Bazaruto is an important area for undefined aggregations of three shark and five ray species.
Grey Reef Sharks regularly aggregate in this area. Dive surveys have recorded 129 sightings, with sightings every year between 2014–2022, except 2016 (Marine Megafauna Foundation unpubl. data 2023). While solitary individuals are observed (15% of total sightings), groups of up to 12 individuals have been recorded. At one rocky reef in the south of the area, multiple individuals were recorded on 90% of surveys at this site (mean = 7 individuals per dive, range = 2–12) (Marine Megafauna Foundation unpubl. data 2023). The drivers of these aggregations are unknown, but they may be associated with feeding, as this species has also been observed feeding on surface baitballs in the area.
Dive surveys recorded 334 sightings of Bull Sharks between 2013–2023, with sightings every year except 2016 (mean = 33 sightings per year; Marine Megafauna Foundation unpubl. data 2023). Bull Sharks are seen in groups of up to eight individuals at 14 sites, although 71% of sightings are from a rocky reef off northeast Bazaruto. Passive acoustic telemetry data show high residency, with individuals spending up to 79% of detected days at rocky reef sites (Marine Megafauna Foundation unpubl. data 2023). While the drivers of aggregations are currently unknown, this species has occasionally been sighted feeding on surface baitballs in the area (up to 10 individuals on a baitball,
R Daly pers. obs. 2023). Predation attempts on large rays have also been witnessed. In addition, 16 of 17 individuals acoustically tagged were female, and pregnant individuals have been observed, suggesting the area may be particularly important for females.
Dive surveys have recorded 146 sightings of Scalloped Hammerheads (69% of total sightings from the Inhambane Province), with the species seen every year between 2015–2022 (except 2016) (Marine Megafauna Foundation unpubl. data 2023). Sightings were from April to November, with higher numbers in the austral winter (June–August). Groups of up to 25 individuals were recorded (mean group size = 7 individuals). Larger groups were observed at 25–35 m rocky reef pinnacles and ridges, nearby to deep drop-offs. While the drivers of these aggregations are unknown, schooling behaviour in this species is observed in other locations (e.g., Bessudo et al. 2011) and has been linked to social and reproductive functions (Gallagher & Klimley 2018).
Spotted Eagle Rays aggregate in this area. Dive surveys recorded 626 sightings between 2013–2023, with sightings every year (except 2016), year-round, with a peak in May–July (Marine Megafauna Foundation unpubl. data 2023). Aggregations up to 60 individuals (mean = 10) have been recorded. Aerial surveys conducted in 2012–2014 (n = 9) recorded an additional 87 sightings, with the species observed travelling in groups of up to 5–7 individuals on three occasions, and a large group of 70 individuals on a single occasion (J Conradie unpubl. data 2023). Although the drivers of these aggregations remain unknown, Spotted Eagle Rays have been observed actively cleaning on reef cleaning stations (15% of sightings with a recorded behaviour [n = 249]; Marine Megafauna Foundation unpubl. data 2023).
Dive surveys recorded 304 sightings of Coach Whiprays from 2017–2023, with sightings every year, throughout the year with a peak in May–September (Marine Megafauna Foundation unpubl. data 2023). This species is almost exclusively seen in this area, with 94% of overall sightings across the Inhambane Province recorded here. The species has been reported in aggregations of up to 10 individuals (mean group size = 4.1 individuals). Although the nature and function of the aggregations are not yet understood, it is possible that they use the area to rest (85% of sightings with behaviour recorded, total n = 107) and to clean (14%), given that this species is commonly sighted at a cleaning station frequented by other rays.
Reef Manta Rays aggregate to clean in Greater Bazaruto. Dive surveys conducted between 2013–2023 have recorded 900 sightings and this species was actively cleaning in 88% of sightings where behaviour was recorded (n = 624; Marine Megafauna Foundation unpubl. data 2023). Surveys have recorded large groups (10–20 individuals) of Reef Manta Rays on 17 occasions (across multiple years) cleaning at the same time, at cleaning stations, where cleaner fishes remove parasites and dead skin off the rays. This is an important behaviour in the species, with 10 of 36 individuals tracked with passive acoustic telemetry spending >3 consecutive hours on a cleaning station (mean visit duration = 25 min, maximum = 8 h; Venables et al. 2020). Apart from the physical/health benefit, cleaning stations are also important locations for social interactions and courtship of Reef Manta Rays (Marshall & Bennett 2010; Perryman et al. 2019).
This area hosts undefined aggregations of Broad Cowtail Rays. Dive surveys recorded 305 sightings between 2013–2023, with sightings every year except 2015 and 2016 (Marine Megafauna Foundation unpubl. data 2023). Sightings were year-round, with a peak in May–August. This species is almost exclusively seen in this area, with 98% of overall sightings across the Inhambane Province recorded here. Aggregations of up to 20 individuals were observed (mean group size = 4.1 individuals). Additionally, 14 individuals were identified in a drone and snorkel survey of a shallow estuary, where this species is often encountered resting on the sandy substrate (Marine Megafauna Foundation unpubl. data 2023). The reason for their aggregations is not yet understood, although it is possible that they use the area to rest (55% of behaviours recorded, n = 66), feed (20%), and clean (20%).
Oman Cownose Rays have been sighted on 10 occasions in the area in total but are observed in large aggregations and landed in high numbers in gill and seine nets. Aerial surveys recorded groups of ~20, ~50, ~200, and ~2,000 individuals in 2012 and 2013 (Marine Megafauna Foundation unpubl. data 2023). More recently, dive surveys in 2019–2023 recorded schools of ~40, ~100, and ~200 individuals and one record of a fever comprising ~1,000 individuals (Marine Megafauna Foundation unpubl. data 2023). This species is also regularly landed in high numbers (up to 250 individuals) at nearby landing sites in Vilanculos, caught in gill and seine nets (A Marshall pers. obs. 2023).
CRITERION D
SUB-CRITERION D1 – DISTINCTIVENESS
Greater Bazaruto contains areas with distinctive attributes for four ray species.
The area is an important cleaning habitat for Smalleye Stingrays. Dive surveys have recorded 24 sightings of this rare species, in 2013–2014 and 2017–2023. Sightings occurred year-round (mean = 3 sightings per year, range = 1–9), with higher numbers in the austral winter (August–September). Active cleaning was observed in 65% of sightings. The Inhambane Province is the only documented area globally where Smalleye Stingrays regularly visit cleaning stations (Boggio-Pasqua et al. 2019). Preliminary data from five individuals acoustically tagged in this area show high residency to cleaning sites e.g., two tagged males had 88% and 97% of detections at one site, over >13 months of tracking (Marine Megafauna Foundation unpubl. data 2023). Telemetry data suggest that dive surveys likely underestimate abundance of this species, as a satellite-tracked male spent 66% of the time in depths inaccessible to divers (>30 m; Marine Megafauna Foundation unpubl. data 2023). Passive acoustic telemetry data (n = 12) further support this, with 70% of detections recorded between midnight and 6 am, when observers are not on the reefs (Marine Megafauna Foundation unpubl. data 2023).
Greater Bazaruto contains important cleaning areas for Shorthorned Pygmy Devil Rays. Dive surveys have recorded 162 sightings from the area, with sightings every year from 2013–2023 (Marine Megafauna Foundation unpubl. data 2023). A cleaning station for Shorthorned Pygmy Devil Rays exists at an 8–20 m deep reef in the Bazaruto Archipelago, one of only two cleaning stations identified for this species in the Western Indian Ocean (Murie & Marshall 2016), which may be a key driver of their visitation to the area. Local dive operators visit this reef on a weekly basis and encounter this species on almost all dives (~90%) at this site (Odyssea Dive Centre pers. comm. 2023).
This is an important cleaning area for Pink Whiprays, which are sighted at rocky reefs (20–30 m deep) and on shallow tidal sand flats throughout the area. Dive surveys recorded 161 sightings (75% of overall sightings from the Inhambane Province), with sightings every year from 2019–2023 (mean = 39 sightings per year, range = 5–52). Pink Whiprays were actively cleaning at cleaning stations in 50% of sightings in which behaviour was recorded (n = 40). Remote Underwater Video cameras deployed in 2021 and 2022 recorded cleaning behaviour on ~40% of deployments (n = 30; Marine Megafauna Foundation unpubl. data 2023). Cleaning behaviour in this species has not been recorded at any other location in the province and may be unique to this area.
Bottlenose Wedgefish also use this area for cleaning behaviour. Reports of cleaning behaviour in wedgefishes are rare, and to our knowledge, the area contains some of the only identified cleaning stations for this species in the Western Indian Ocean. Dive surveys have recorded 262 sightings, with sightings every year from 2013–2023 (Marine Megafauna Foundation unpubl. data 2023). Thirty-five sightings were recorded prior to 2019. After 2020, when dedicated survey effort began for this species, a mean of 57 sightings per year were recorded (range 46–80 sightings per year). In 30% of sightings for which behaviour was recorded (n = 129), the species was observed actively cleaning at cleaning stations. These typically are specific sandy areas adjacent to rocky reefs (20–30 m deep) that are also used as cleaning stations by other sharks and rays. Preliminary telemetry data show high residency, with three acoustically tagged individuals spending 45%, 73%, and 84% of detected days at these sites (Marine Megafauna Foundation unpubl. data 2023).
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