Introduction
The ornate eagle ray Aetomylaeus vespertilio (Bleeker, 1852) is one of the largest and least studied eagle rays (Family Myliobatidae), and is distributed in the Indo-West Pacific from Mozambique to Australia, including the Red Sea, Seychelles, Maldives, India, China, Indonesia, Philippines, Malaysia and Taiwan (White and Kyne, Reference White and Kyne2016). It is typically found in muddy bays and near coral reefs (Last et al., Reference Last, White, de Carvalho, Seret, Stehmann and Naylor2016). Unfortunately, this species is highly vulnerable to demersal fishing gears, particularly trawls and bottom-set gillnets, that are commonly used in inshore areas.
The mangrove whipray Urogymnus granulatus (Macleay, 1883) is a large-bodied stingray (Dasyatidae) with a restricted distribution and that is landed infrequently in the Indo-West Pacific region (Last, Reference Last, Last, White, de Carvalho, Seret, Stehmann and Naylor2016). The ornate eagle ray and mangrove whipray are listed as ‘endangered’ (White and Kyne, Reference White and Kyne2016) and ‘vulnerable’ (Manjaji Matsumoto et al., Reference Manjaji Matsumoto, White, Fahmi Ishihara and Morgan2020), respectively, in the IUCN Red List of Threatened Species. Their population trends globally have been assessed as decreasing, indicating a pressing need for conservation efforts.
The Gulf of Mannar (GoM) is a globally recognised marine ecosystem from a biodiversity perspective, located off south-east India between the maritime state of Tamil Nadu and the west coast of Sri Lanka. It extends from Dhanushkodi of Ramanathapuram to Kanyakumari district, has Palk Bay in the north and the Indian Ocean in the south. An estimated 4223 species of flora and fauna have been reported, including species of commercial and ecological importance (Kumaraguru et al., Reference Kumaraguru, Edwin, Marimuthu and Jerald2006). GoM has a diverse array of fishing vessels, ranging from non-mechanized to motorized, actively operating in its waters. The region stretching from Pamban to Keelakarai is typically fished by single-day trawlers and these vessels are known to land several batoids, including threatened rays.
In the present study, two ornate eagle rays and one mangrove whipray were caught by single-day trawlers in the GoM. These specimens represent the largest sizes ever reported globally for both species. With the exception of a few reports from the south-west coast, especially from Kochi, there has been scarce documentation of eagle ray catches by traditional and commercial gears operating in Indian waters. Biological observations from these specimens are provided.
Materials and methods
The data on all ray specimens were collected from the Pamban Therkuvadi Fish Landing Centre (FLC), GoM, Tamil Nadu, south-east coast of India in July 2021 and August 2022. The fishing grounds of the trawler are shown in Figure 1. Morphometrics of the fish was measured using a graduated measuring tape and scale and expressed in cm. Weight measurements were recorded up to an accuracy of 0.01 g using an electronic balance.
Figure 1. Operating locations of fish trawler in the Gulf of Mannar.
Results and discussions
Fishing pattern in the GoM
Fishermen typically commence their journey at 06:00 and return by 08:00 the following day. During a single trip, each vessel makes 4–6 hauls, and the total operating time ranges between 12 and 18 h. Single-day fish trawls that operate within the Ramanathapuram district of Tamil Nadu (GoM) are active on Mondays, Wednesdays and Fridays each week. Rays are a bycatch in the activities of mechanized single-day trawlers (20–22.5 m in overall length; 180 hp engine power). The vessels operate at depths ranging from 50 to 100 m and a distance of 28–35 km off Pamban Island. There is a legal ban period of 61 days for mechanized vessels along the east coast of India, which begins on the 15th of April and ends by mid-June. Fishers typically venture to deeper waters immediately after the trawl ban to maximize their catch. During July and August, all three record-sized rays that were landed were either pregnant or in the post-partum stage. This observation is indicative of a pupping season off Pamban Island. The gut contents and chief fishery resources landed were more or less similar, reflecting the co-existence of these rays with other small pelagics and demersal fishes.
Ornate eagle ray Aetomylaeus vespertilio
A pregnant ornate eagle ray measuring 384 cm DW and weighing 530 kg, the largest size ever reported for the species globally (Figure 2A), was landed at Pamban Therkuvadi FLC on 19 July 2021. The maximum reported sizes of the species reported previously were 240 cm DW (White et al., Reference White, Last, Stevens, Yearsley, Fahmi and Dharmadi2006) to 300 cm DW (Last, Reference Last, Last, White, de Carvalho, Seret, Stehmann and Naylor2016), and 190 cm DW in Indian waters (Paul, Reference Paul2011).
Figure 2. Record size Aetomylaeus vespertilio and Urogymnus granulatus (A) A. vespertilio landed on 19 July 2021; (B) full-term embryos of A. vespertilio landed on 19 July 2021; (C) U. granulatus; (D) A. vespertilio landed on 12 August 2022.
Three full-term embryos (Figure 2B; Table 1) were present in the uterus. The number (and range of diameters) of small, medium and large oocytes were 32 (0.64–0.87 cm), 11(1.1–1.9 cm) and 6 (5.2–6.5 cm), respectively. The stomach of this specimen contained bigeye scad Selar crumenophthalmus (n = 29; 16–21.5 cm total length), all in an undigested state.
Table 1. Measurements of pups of A. vespertilio
Another large, female ornate eagle ray (360 cm DW; 453 kg total weight; Figure 2D) was also landed at the same landing centre on 12 August 2022. The stomach of this specimen was empty. Enlarged uterus contained vascular trophonemata. Oocytes were split or disintegrated, perhaps indicates reproductively mature female, which underwent a recent parturition. The morphometric measurements of both specimens are given in Table 2.
Table 2. Morphometrics of record sized A. vespertilio and U. granulatus caught from Gulf of Mannar
Mangrove whipray Urogymnus granulatus
A mangrove whipray (Figure 2C) of 153 cm DW and 150 kg total weight was landed at the same FLC on 28 July 2021. This specimen exceeded the previously reported maximum size of 141 cm DW (White et al., Reference White, Last, Stevens, Yearsley, Fahmi and Dharmadi2006). The major gut contents of the specimen comprised pigface bream (Lethrinus spp.), thumbprint monocle bream (Scolopsis bimaculata), goatfish (Upeneus spp.), lesser sardine (Sardinella spp.), silverbiddies (Gerres spp.), yellow-striped scad (Selaroides leptolepis) and octopus (Octopus vulgaris), all in semi-digested states. The uterus was empty with highly vascular and developed trophonemata, perhaps indicating a post-parturition.
Neither the ornate eagle ray nor mangrove whipray represent an established fishery in India, as they are primarily caught as bycatch or are considered unusual catches in trawls, gillnets or long lines. Occasional catches from commercial trawlers and gillnetters have been reported particularly in Cochin Fishing harbour, Kerala (Paul, Reference Paul2011; Benjamin et al., Reference Benjamin, Jose, Kurup and Harikrishnan2012; Bineesh et al., Reference Bineesh, Akhilesh, Sajeela, Abdussamad, Gopalakrishnan, Basheer and Jena2014). The geographic range of ornate eagle ray in the eastern Arabian Sea shows distribution between Cape Comorin and Mumbai and between Vizag and Cape Comorin along western Bay of Bengal (White and Kyne, Reference White and Kyne2016). Similarly, mangrove whipray has a still limited range along Indian coast between off Mangalore of south-west coast and Point Calimere of south-east (Manjaji Matsumoto et al., Reference Manjaji Matsumoto, White, Fahmi Ishihara and Morgan2020). Except reports from Kerala and current study in Tamil Nadu, there is limited information on the landing of these rays in other maritime states of India, perhaps due to uniqueness of GoM, one of the richest hotspot of marine biodiversity.
Data
The datasets generated and/or analysed during the current study are not publicly available as the manuscript contains such datasets being submitted to a scientific journal for the first time, but are available from the corresponding author on reasonable request.
Acknowledgements
The authors are thankful to the Director of ICAR-CMFRI and Head in Charge, Mandapam Regional Centre for providing guidance and facilities to carry out this study. The authors are also grateful to the trawl fishers in Pamban Therkuvadi and elasmobranch processing unit in Rameswaram for their co-operation while taking measurements and data gathering.
Author contributions
All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Remya Lalitha, Sujitha Thomas, Shoba Joe Kizhakudan, Thirumalaiselvan Shanmugam, Gandhi Ayyakannu, Midhun Muthayan, Rajkumar Raja, Vetrivel Vedhagiri, Rajendran Umayan, Shanmuganathan Kalimuthu and Prakash Murugesan. All authors read and approved the final manuscript.
Financial support
This work was supported by fund received under the in-house research project ‘Developing management strategies for sustainable exploitation and conservation of elasmobranchs in Indian seas’. First author has received research support from ICAR-CMFRI.
Competing interest
None.
Ethical standards
The study was conducted on rays caught by fishermen of Pamban Island using commercial fishing gears. The study also utilized observation from a local dry fish unit.
