true

ISRA FACTSHEETS

ASIA REGION

ISRA FACTSHEETS

ASIA REGION

Black Rock & the Twins ISRA

70/122

Black Rock & the Twins ISRA

Black Rock & the Twins

Summary

Black Rock & the Twins is located on the west coast of the Malay Peninsula in southern Myanmar. The area consists of three small rocky island formations, characterised by coral reefs. Within this area there are: threatened species (e.g., Oceanic Manta Ray Mobula birostris); range-restricted species (Ranong Guitarfish Rhinobatos ranongensis); and undefined aggregations (e.g., Oceanic Manta Ray).

Black Rock & the Twins

Black Rock & the Twins

DESCRIPTION OF HABITAT

Black Rock & the Twins is located along the west coast of the Malay Peninsula in the Tanintharyi state of southern Myanmar. The area encompasses three small rocky island formations: Black Rock (a small limestone islet), and North Twin and South Twin (both small tree-covered granite boulder islands). The area is characterised by coral reefs and is connected by pelagic waters.

Black Rock & the Twins is influenced by the boreal summer monsoon (May–October), which sees higher precipitation levels throughout the region (Xing et al. 2016). This region is subject to large amplitude internal waves common in the Andaman Sea. Alongside the seasonal monsoon, these internal waves contribute to nutrient and temperature mixing (Wall et al. 2012).

This Important Shark and Ray Area is benthopelagic and is delineated from inshore and surface waters (0 m) to 60 m based on the habitat features of the area.

CRITERION A

VULNERABILITY

Two Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened Species regularly occur in the area. These are the Endangered Oceanic Manta Ray (Marshall et al. 2022) and the Vulnerable Ranong Guitarfish (Dulvy et al. 2021).

CRITERION B

RANGE RESTRICTED

This area holds the regular presence of Ranong Guitarfish as a resident range-restricted species. This species’ occurrence is seasonal and appears to be amplified during the positive phase of the Indian Ocean Dipole (IOD), with observations by divers in December 2019, January 2020, March 2020, February 2023, and December 2023 of Ranong Guitarfish resting in groups on the seafloor in close proximity to one another (5–10 individuals, max = 20; T Ko Gyi pers. obs. 2019; S Arunrugstichai pers. obs. 2023; Smiling Seahorse pers. comm. 2023). Sightings were at Black Rock and Twin Rocks, between 25–30 m depth and the species has not been recorded in any adjacent areas where diving activities are regular. This species only occurs in the Bay of Bengal Large Marine Ecosystem.

CRITERION C

SUB-CRITERION C5 – UNDEFINED AGGREGATIONS

Black Rock & the Twins is an important area for undefined aggregations of two species of rays.

Since 2011, 276 encounters of Oceanic Manta Rays have been recorded during scientific dive surveys (Marine Megafauna Foundation [MMF] unpubl. data 2020) and from opportunistic citizen science submissions (MantaMatcher.org unpubl. data 2023). Research expeditions were conducted annually between 2012–2020 and contributed most recorded sightings from the area. From the 276 encounters, 216 individual rays were identified using photo-identification, with the remaining 60 encounters comprised of resightings of these individuals. The rocky islets of Black Rock, North Twin, and South Twin account for the majority of sightings in this area, with Black Rock home to over 95% of Oceanic Manta Ray sightings. This is potentially reflective of survey effort, whereby the majority of research expeditions only visited Black Rock, and North Twin and South Twin were only visited as a backup if encounters at Black Rock were unsuccessful. Black Rock is comprised of cleaning stations where small cleaner fish remove dead tissue and parasites from other fish. Oceanic Manta Rays were observed cleaning on 31% of encounters at Black Rock (MMF unpubl. data 2020). These sites potentially function as an important socialisation hub, with up to 28 individuals identified on a single day. Pre-copulatory behaviour, such as courtship trains or chasing has been observed on some days with more than 15 individuals (MMF unpubl. data 2020). Of the 38% of manta encounters with a recorded age class, 92% were mature based on clasper development, mating scars, or pregnancy (based on Marshall & Bennett 2010; MMF unpubl. data 2020; MantaMatcher.org unpubl. data 2023). Pregnant Oceanic Manta Rays have been observed three times on Black Rock (MMF unpubl. data 2020). Oceanic Manta Rays have shown regular and predictable movements between southern Myanmar and Thailand. Photo-identification data from 2003–2020 has shown that 23 individuals have moved between aggregation sites of Black Rock, North Twin, and South Twin in Myanmar, and the Similan Islands, Koh Lanta, Hin Muang, and Hin Daeng in Thailand (MantaMatcher.org 2023; MMF unpubl. data 2020), however the migration route they follow is not well understood.

Ranong Guitarfish have been observed by SCUBA divers at Black Rock when the diving season overlaps with the IOD. They were first observed at ~26 m depth during a diving trip to Black Rock in December 2019 (Ko Gyi pers. obs. 2019). During dive trips in January 2020, ~20 individuals were observed resting on the seafloor in close proximity to each other. In February 2023, a pregnant Ranong Guitarfish was observed caught in a gillnet as bycatch on a drift gillnet fishing boat that was fishing at the depth of 60 m near Black Rock (S Arunrugstichai pers. obs. 2023). The pregnant Ranong Guitarfish was not released and the pups were seen aborted due to stress. The gillnet fishers communicated that it was common for them to catch Ranong Guitarfish in this area. Ranong Guitarfish were recorded again in December 2023 during the positive phase of the IOD (Smiling Seahorse pers. comm. 2023). Observations from SCUBA divers in December 2023 were of >10 individuals in proximity to each other on the seafloor at the deeper end of the slope of Black Rock. Ranong Guitarfish have been observed by SCUBA divers at North Twin when the diving season overlaps with the IOD. They were observed during diving trips at North Twin in December 2019, January 2020 (S Arunrugstichai pers. obs. 2023), and again in December 2023 (Smiling Seahorse pers. comm. 2023). During the dive season in 2019/2020, SCUBA divers observed 5–10 individuals laying on the seafloor during the dives at 25–30 m depth at North Twin.

Further information is required to determine the nature and function of these aggregations.

Black Rock & the Twins

SUBMIT A REQUEST

ISRA SPATIAL LAYER REQUEST

To make a request to download the ISRA Layer in either a GIS compatible Shapefile (.shp) or Google Earth compatible Keyhole Markup Language Zipped file (.kmz) please complete the following form. We will review your request and send the download details to you. We will endeavor to send you the requested files as soon as we can. However, please note that this is not an automated process, and before requests are responded to, they undergo internal review and authorization. As such, requests normally take 5–10 working days to process.

Should you have questions about the data or process, please do not hesitate to contact us.

    * indicates required

    Industry or sector (*)

    Under the terms and conditions of our User License Agreement , full and appropriate acknowledgement is required in any materials and publications derived from the data (and copies should be sent to the IUCN SSC Shark Specialist Group through the contact form). For any publications making substantial use of the data, the ISRA welcomes the opportunity for co-authorship, collaboration, and to comment prior to publication.


    Furthermore, we need to know whether you are a commercial or non-commercial user. Non-commercial includes scientific research, education or conservation. Commercial is defined as follows: any use by, on behalf of, or to inform or assist the activities of a commercial entity (that operates ‘for profit’) or use by a non-profit for the purposes of revenue generation

    Type of use(*):

    Please specify which layer (ex. all layers, layers within a specific Region, layers within a Jurisdiction or a single ISRA): Purpose (*):

    Please provide a description of how you intend to use the ISRA GIS Dataset. The more details you provide, the faster we can respond to your request. We may require further clarification prior to providing access. (min. 100 characters – max 1,000 characters)



    File format request (*)

    By providing your personal data, you consent to its processing as described below. The IUCN SSC Shark Specialist Group will use the information you provide on this form to send the documents you requested. You can change your mind at any time by writing to the ISRA Data Coordinator www.sharkrayareas.org/contact. All personal details provided will be treated with respect. For any information you can visit our Privacy Policy.
    Please read the User License Agreement and ISRA Layer Metadata Description

    This form uses Google reCaptcha to reduce spam. Privacy - Terms