First description of foetus of giant manta ray foetus Mobula birostris (Walbaum 1792) from Kochi, Kerala, Southwest India (North East Arabian Sea)

doi:10.21203/rs.3.rs-1750734/v1

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First description of foetus of giant manta ray foetus Mobula birostris (Walbaum 1792) from Kochi, Kerala, Southwest India (North East Arabian Sea)

https://doi.org/10.21203/rs.3.rs-1750734/v1

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Giant Manta Ray is assessed as Vulnerable by IUCN and has a very low reproductive capacity. India is also one of the major manta fishing countries; however, commerce in gill plates is not well documented. With information of these gentle giants scanty in literature, record of morphological and morphometric data pertaining to Mobula foetus from this region is very important. The disc length (DL) of the foetus recorded in Kochi was only 30 mm and the foetus already had pigmentation patterns in the ventral portion of the cephalic horn and displayed the presence of an umbilical attachment. The presence of the gravid female is not a solitary event and there are many such cases which may have gone unnoticed. Together with our recent findings, and previous records, this data reinforces the importance of the west coast as potential reproduction grounds for M. birostris. This information is crucial for the establishment and progression of conservation measures for this migratory species.

Mobula birostris. Foetus

Northeast Arabian Sea

manta

first description

The Giant Manta Ray (Mobula birostris) is a large marine vertebrate with a disc width reported upto 910 cm (White et al. 2006) and weight of 2 tonnes (Kunjipalu and Boopendranath, 1981) found over continental shelves and near oceanic islands widely diffused in all oceans and adjacent seas, often extending their range into warm temperate latitudes. This species is reportedly the largest among the genus Mobula. Mobulids are filter feeders, unfurling the cephalic horns out front and funnelling water towards their mouth to extract the tiny animals they eat. Mobula birostris rays are assessed as Vulnerable by the International Union for Conservation of Nature (IUCN, 2019). This is because they are often targeted by fishers for their gill plates to be used in a pseudo-medicinal soup called PengYuSai which is made of boiled manta gills, seahorses, and pipefish and is supposedly a remedy for fever, chickenpox and breastfeeding mothers. However, large numbers of devil rays die accidentally when caught as bycatch each year as they become entangled in fishing nets while foraging for food. Species of the genus Mobula have a very low reproductive capacity (i.e., giving birth to a single large pup at unknown intervals (Notarbartolo di Sciara and Serena 1988) are ovoviviparous with a long gestation period of one and a half years (Herbert 2012; Marshall et al. 2008, Mendonça et al. 2012). India along with Indonesia, Sri Lanka comprise the top three manta fishing countries and account for an estimated 90 percent of the world’s manta catch and target mantas for their gill plates. However, commerce in gill plates is not well documented (Raje et al. 2002), although an estimate of the total volume of the gill plate trade has been produced from an analysis of market surveys in the major manta ray gill plate markets (Nair et al. 2013). During the year 2020 an estimated 12438 tonnes of rays was landed in India and in 2021, an estimated 133 t of Mobula birostris was landed in Kerala. (CMFRI 2021) The objective of this study is to record the measurements of a Mobula birostris foetus of a female caught accidentally in the region of Kochi, Kerala. This is the first record of morphological and morphometric data regarding a Mobula foetus from this region.

During the regular fishery monitoring programme of the ICAR-Central Marine Fisheries Research Programme, the landing of 20 individuals of the species of Mobula birostris at Cochin Fisheries Harbour which was caught incidentally in the gillnets operated off Kerala on the North East Arabian Sea were recorded on the 20 November 2021. Measurements of the adult pregnant mobulid ray were recorded on the field (Table 1) and the gill plates and abdominal cavity was also examined for the collection of samples including stomach contents. A foetus was detected inside on dissection of the uterus since the uterus was dilated. The foetus was subsequently removed and transferred to the Laboratory of ICAR - Central Marine Fisheries Research Institute (ICAR-CMFRI). In the laboratory, 21 morphological measurements were recorded as per Marshall et al. (2008). Following this, the foetus was fixed in 4% formaldehyde and deposited in the collection of the Fisheries Division Laboratory. Additionally, the proportions of the body were calculated based on the percentage of the disc width (% DW). The identification of species was made according to Notarbartolo di Sciara (1987; 2016); Serena (2005); and Capapé et al. (2015). The lengths (disc width, disc length, total length, etc.) were measured to the nearest 0.1 cm and the weight to the nearest kilogram (kg). The freshly collected specimens were photographed, a small piece of white muscle tissue from the ventral surface was collected for DNA isolation, later fixed in formalin, and stored for future reference

This report presents new diagnostic features for Mobula birostris foetus India and is the first report from Indian waters. The present study provides short taxonomic accounts with morphometric data for the species, along with photographs.

Material examined FFD 2022 -1, 274.32 mm TL; 287.64 mm DW, male, collected from gill net catch, 220 17' 59'' N, 680 07' 92''E as a bycatch of tuna landings off Calicut, landed at Cochin Fisheries Harbour, Collection date: 20 November 2021, collected by the first and second authors from the said harbour. The morphometric measurements of Mobula birostris was compared with following Ishihara et al. (1993), Current study materials were deposited in the Finfish Fisheries Division Laboratory of the ICAR -Central Marine Fisheries Research Institute (CMFRI), Kochi, Kerala, India.

Description: The adult Mobula birostris is easily recognised by the absence of any white marking on the black dorsal fin which distinguishes it from the Mobula mobular. Though there are reports of adult landings in the different harbours, there are no reports of Mobula foetus from Indian waters. The one available in literature is of a foetus with a disc length of 586 mm, a disc width of 1370 mm and a total weight of 23.6 kg from Tumbes, Peru (Mariano Cabanillas et al. 2019)

Order Myliobatiformes

Family Myliobatidae Bonaparte, 1835

Genus Mobula Rafinesque, 1810

Raja birostris Walbaum 1792:535

Description: On dissection of the adult, the foetus was observed in total (Fig. 1). The mobulid displayed a fleshy colour on the dorsal surface; ventral surface displayed a whitish-creamy colour and a slight pinkish tone on the dorsal surface. Pigmentation pattern was noticed on the cephalic fin tip as a band (Fig. 2) and the outer surfaces of the cephalic fins were primarily skin tone in colour. Colours became fainter posterior to the gill openings. Darker tones were observed from the cloaca to the tips of the pectoral fins. Markings of the gill filaments were visible through the skin on the dorsal surface as darker tones. (Fig. 2). Eyes were present as two dark black balls placed laterally. An umbilical-like stalk was noticed which terminated in a 10 mm reddish navel on the ventral side (Fig 3). The umbilical stalk was inserted at the point below gill slits on the ventral surface. The tail had a caudal spine at its base, character key for Mobula birostris (Fig. 1). Patches of dermal denticles were presented in the ventral and dorsal surfaces of the body.

The disc length (DL) of the foetus recorded in Kochi was only 30 mm which was much smaller compared to the record of Peru (586 mm) and quite similar to that recorded in Ecuador (180 mm) representing 108.52% of the DL. However, the recorded weights display a much greater variation. Those recorded in Peru were substantially higher (185.83%) than those reported from Ecuador. These biometric differences could be due to possible differential stages in growth.

Dewar et al. (2008) suggests that the presence of M. birostris is directly related to the productivity of the area which further indicates that the Western coast of India is a highly productive area of the Western Indian Ocean since in 2021 an estimated 133 t was landed in Kerala alone. Besides the gravid manta indicated in this document, there has been previously recorded instances of other mobulids between August 2012 and May 2013 in this area. This indicates that the occurrence of gravid mantas is not an exclusive event. Together with our recent findings, and previous records, this data reinforces the importance of the westcoast of India as potential reproduction grounds for M. birostris. This information gathered from the west coast of India is crucial for the establishment and progression of conservation measures for this migratory species.

Researchers believe that sexually mature female giant devil rays have an average wing-to-wing span of 16.5 feet (Stevens et al. 2018). The average measurement of a newborn pup is 1 meter (3.28 ft). There has been very few studies on the reproductive biology of this species; hence the results reported in this study tally with this reproductive record. Regarding weight and size at birth, the two captive mobulas born in Japan in 2007 (Okinawa Churaumi Aquarium) had disc widths of 1.8 and 1.9 meters, and the latter animal weighted (68.5 kg). So, it could indicate that the foetus described herein which measured (DW=125 mm; weight: 265 g) was in a primitive stage of foetal development. In addition, it was observed that the foetus already had pigmentation patterns in the ventral portion of the cephalic horn that in M. birostris these patterns develop before being born, however it cannot be confirmed that the registered patterns are definitive, as given by Marshall et al. (2008). The foetus of M. birostris displayed the presence of an umbilical attachment, which was the remnant of the yolk sac the results which was similar to that of Marshall et al. (2008).

Besides the gravid manta indicated in this document, Mobula birostris has been regularly recorded from the Western coast of India during the last few years (CMFRI, 2021). This points to the fact that the presence of the gravid female is not a solitary event and there are many such cases which may have gone unnoticed. Together with our recent findings, and previous records, this data reinforces the importance of the west coast as potential reproduction grounds for M. birostris. This information is crucial for the establishment and progression of conservation measures for this migratory species.

Ethical Approval and Consent to participate

There is no ethical issue concerning this article.

Human and Animal Ethics

No animal testing was performed during this study.

Consent for publication

All authors agree to its submission and the Corresponding author has been authorized by co-authors.

Availability of supporting data

Not applicable

Competing interests

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Funding

The work was funded by World Wide Fund for Nature

Sampling and Field Studies

The sample for this study was collected from the fish landing centre of the Cochin Fisheries Harbour, which was caught as bycatch in the commercial trawler. Necessary permits for sampling and observational field studies have been obtained by the authors from the competent authorities and are mentioned in the acknowledgments, if applicable. The study is compliant with CBD and Nagoya protocols.

Authors' contributions

Sample collection & manuscript writing & data analysis –, VN Morphometric measurements– RJN, VKN, SAT; Sample Identification – RJN, VN, SKTS, PM Manuscript concept –RJN All authors read, incorporated, and approved the manuscript.

Disclaimer

The marine fish landings data used in this study/publication are research data of ICAR-CMFRI collected through diachronic primary surveys following a stratified multistage random sampling design across the coastline of mainland India.

Acknowledgements

The authors are thankful to Dr. A. Gopalakrishnan, Director, Central Marine Fisheries Research Institute, Kochi for providing facilities and the Indian Council of Agricultural Research, New Delhi for providing the research grant to carry out the work. VN is thankful to the WWF for providing the funding, RJN, SKTS, PM, VKM, SAT is thankful to the Director, ICAR-CMFRI for the facilities to carry out this work.

Authors' information

Corresponding author

Rekha J. Nair

Principal Scientist

ICAR-Central Marine Fisheries Research Institute, Kochi

[email protected]

Co-author

Vishnu Nair M S

Principal Investigator, WWF, India.

Co-author

Sunil K T S

Senior Technician

ICAR-Central Marine Fisheries Research Institute, Kochi

Co-author

Pakrimuthu, S

Technician

ICAR-Central Marine Fisheries Research Institute, Kochi

Co-author

Vishnupriya K M

ICAR-Central Marine Fisheries Research Institute, Kochi

Co-author

Sangeetha A T

ICAR-Central Marine Fisheries Research Institute, Kochi

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Table 1 Morphometry in cm of the Mobula birostris embryo and adult collected in the Cochin Fisheries Harbour and (expressed in % DW)

Body Parameters
Adult	In cm	% DW
Total Length	274.32
Disc length	142.31
Disc width	287.64
Horn length	46.02	15.999
Inter horn length	61.3	21.311
Mouth length	54.85	19.069
Gill slit length	38.5	13.385
Total slits top to bottom length	41.43	14.403
Last slit length	27.54	9.574
Inter gill slit length	37.33	12.978
Tail length	131.01	45.547
Pup	(in mm)
Total Length	18.8
Length of disc	15.8
Disc length till insertion	12.5
Disc width	30
Snout length	4.8	16.000
Eye diameter (Horizontal)	0.6	2.000
Eye diameter (Vertical)	0.8	2.667
Interorbital distance	7.7	25.667
Mouth width	4.4	14.667
Tail length	47.5	158.333
Insertion point of spine	18	60.000
Head length (tip of snout to inner end of ist gill opening)	5.5	18.333
Gill slits (horizontal distance between 1st gill slits)	3.9	13.000
Gill slits (horizontal distance between 2 nd gill slits)	3.6	12.000
Gill slits (horizontal distance between 3 rd gill slits)	3.1	10.333
Gill slits (horizontal distance between 4th gill slits)	2.4	8.000
Gill slits (horizontal distance between 5 th gill slits)	1.4	4.667
Snout to anus	16.4	54.667
Pre oral distance	12.4	41.333
Tail width at base of sting	0.37	1.233
Tail height at base of sting	0.352	1.173
Sting length	1.242	4.140
Pectoral insertion to sting origin	1.944	6.480
Clasper length	1.7	5.667
Upper toothband length	3.5	11.667
Lower toothband length	3.4	11.333
Anterior projection	4.2	14.000
Pre dorsal distance	14.4	48.000
Dorsal fin base length	1.5	5.000
Dorsal fin vertical height	2	6.667
First interbranchial	2	6.667
Fifth interbranchial	1.3	4.333
Cephalic fin length	3	10.000
Cephalic fin width	2.2	7.333
Weight	265 g

No competing interests reported.

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First description of foetus of giant manta ray foetus Mobula birostris (Walbaum 1792) from Kochi, Kerala, Southwest India (North East Arabian Sea)

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