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ISRA FACTSHEETS

WESTERN INDIAN OCEAN REGION

ISRA FACTSHEETS

WESTERN INDIAN OCEAN REGION

Bodu Hithi Kandu ISRA

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Bodu Hithi Kandu ISRA

Bodu Hithi Kandu

Summary

Bodu Hithi Kandu is located in west North Malé Atoll in the central Maldives. This area encompasses a channel connecting the inner atoll lagoon to the open ocean. In the middle of the channel, there is a submerged pinnacle reef with several bays with sandy substrate and caves. In the southern channel lies the northern corner of Rasfari, a shallow flat reef. This area partially overlaps with a Marine Protected Area. Within this area there are: threatened species (e.g., Whitetip Reef Shark Triaenodon obesus); reproductive areas (Reef Manta Ray Mobula alfredi); feeding areas (Reef Manta Ray); and undefined aggregations (Whitetip Reef Shark).

Bodu Hithi Kandu

DESCRIPTION OF HABITAT

Bodu Hithi Kandu is located in the northern-central Maldives archipelago which sits centrally upon the Chagos-Laccadive Ridge (Stevens & Froman 2019). This area is mainly located in a major channel in western North Malé Atoll. Channels, known locally as kandu, are recognised by high current flow (Stevens & Froman 2019). This area is composed of three sites: Boduhithi Kandu, Boduhithi Thila, and North Rasfari.

Boduhithi Kandu (also known as Hithi Kandu) is a smaller channel within this area on the outer edge of the atoll. Its deepest part at the edge of the atoll is ~30 m and becomes shallower (~2 m) when reaching Boduhithi Faru which is a lagoon with sandy substrate and a shallow, sloping reef at the inner edge of the major channel.

Boduhithi Thila sits in the centre of the mouth of the major channel. Thila is the local name for underwater pinnacle reef where the top of the reef is completely submerged, even during low tide (Godfrey 2023). The thila is 8 m at its shallowest point and ~30 m at its deepest point. The thila is split into two parts with a channel running between, with a sandy substrate and coral bommies. Incoming currents bring in a high density of zooplankton (Armstrong et al. 2021).

North Rasfari is located in the southern entrance of the major channel, bordering the northern corner of Rasfari reef with calm, shallow environments at 5 m depth (Godfrey 2023).

The weather in the Maldives is strongly influenced by the South Asian monsoon, especially the northern and central atolls as these are closer to the Indian subcontinent (Anderson et al. 2011). Two monsoons occur annually in Maldives: the southwest monsoon (known locally as Hulhangu), from May to November, and the northeast monsoon (known locally as Iruvai), from January to March, with transitional periods in December and April (Shankar et al. 2002; Anderson et al. 2011). The southwest monsoon increases average rainfall and wind speeds, causing rougher seas and reduced visibility; in contrast, the northeast monsoon usually brings clear waters (Stevens & Froman 2019).

The Maldives archipelago disrupts the flow of the monsoon-driven North Equatorial Current as it crosses the Indian Ocean (Schott & McCreary 2001) which creates a current flow through the channels of the Maldives (Sasamal 2006). The strongest lunar currents can overcome the prevailing monsoonal currents through the tidal suction mechanism along the channel’s outer edges (Stevens 2016).

This area partially overlaps with a Rasfari Marine Protected Area which encompasses North Rasfari and a part of Boduhithi Thila.

This Important Shark and Ray Area is benthopelagic and is delineated from inshore and surface waters (0 m) to 40 m based on the bathymetry of the area.

CRITERION A

VULNERABILITY

Two Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened SpeciesTM regularly occur in the area. These are the Vulnerable Whitetip Reef Shark (Simpfendorfer et al. 2020) and Reef Manta Ray (Marshall et al. 2022).

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Bodu Hithi Kandu is an important reproductive area for one ray species.

Data collected between 2007–2022 showed 15 courtship events by 12 Reef Manta Rays at Boduhithi Thila and 16 courtship events by 13 Reef Manta Rays at North Rasfari (IDtheManta unpubl. data 2007–2022). During this period, 63 pregnant females were recorded: 36 were in their 4th trimester, 20 were in their 3rd trimester, and seven were in their 2nd trimester (IDtheManta unpubl. data 2007–2022). The gestation time of the Reef Manta Ray is reported to be one year (Stevens 2016). Females are determined to be pregnant by the presence of extended abdomens by trained researchers (Stevens 2016). These researchers can establish the trimester using the size of the rounded belly through sight. Using photo-identification, the pregnancy periods can be tracked for re-sighted Reef Manta Rays. Pregnancy in Reef Manta Rays has been verified in 2018–2019 using contactless ultrasound scanning in other sites of the Maldives (Froman et al. 2023). Additionally, six courtship events have been documented with photographic evidence in this area (Stevens et al. 2018).

CRITERION C

SUB-CRITERION C2 – FEEDING AREAS

Bodu Hithi Kandu is an important feeding area for one ray species.

Reef Manta Rays aggregate when tidal movements bring large concentrations of zooplankton (Armstrong et al. 2021) which occurs at the outer entrance of the channel in this area. Between 2007–2022, 48% (n = 161) of all Reef Manta Ray sightings (n = 336) documented feeding events in the channel by 94 Reef Manta Rays in the northeast monsoon season (IDtheManta unpubl. data 2007–2022). At least seven aggregations have been recorded of Reef Manta Ray feeding between 2014–2020 with a range of 9 to 25 individuals. In this area, high concentrations of plankton drive group feeding behaviour to maximise food intake and minimise energy expenditure (Stevens 2016).

CRITERION C

SUB-CRITERION C5 – UNDEFINED AGGREGATIONS

Bodu Hithi Kandu is an important undefined aggregation area for one shark species.

Data were collected from a citizen-science program known as the Sharkwatch project which was a government-led initiative between 2009–2019 (Maldives Marine Research Institute [MMRI] unpubl. data 2023). Data were collected by experienced dive guides using the roving diver technique where surveyors can swim in any direction and count the number of individuals encountered by species during one-hour dive surveys.

From the ~1,110 sites surveyed in the Maldives, this area has been identified as one of the most important aggregations for the Whitetip Reef Shark (MMRI unpubl. data 2023). Sharkwatch surveys conducted over ten years in this area (2009–2019; n = 839) showed that Whitetip Reef Sharks are regularly present aggregating at this area with a mean encounter rate of five sharks/hour (MMRI unpubl. data 2023). On 92% of surveys (n = 773), at least one Whitetip Reef Shark was encountered and on 13 surveys, aggregations of >15 Whitetip Reef Shark/hour were observed in 2013–2015 and in 2017–2019 (MMRI unpubl. data 2023). Whitetip Reef Shark are observed in both monsoon seasons. In 2013, encounter rates of ~20 Whitetip Reef Sharks/hour were observed in each season (MMRI unpubl. data 2023). Further information is needed to understand the nature and function of these aggregations.

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