Reproductive biology and diet composition of Rhynchobatus laevis (Bloch and Schneider, 1801) (Rhinopristiformes:Rhinidae) from the northern Indian Ocean

Abstract

Large sized batoids particularly wedgefishes are highly vulnerable to fishing and yet very few studies have been published on their biology. The reproductive biology and feeding habit of the Rhynchobatus laevis (Bloch and Schneider, 1801) collected off the north-west coast of India, Arabian Sea, northern Indian Ocean is presented. A total of 328 individuals, in the size range from 44.0 to 290 cm total length (TL), 300 to 94000 g total weight (TW) were used for the study. The length-weight relationships were significantly different between the sexes (p<0.001). Co-efficients ‘a’ and ‘b’ of the length-weight relationship were estimated as 0.009412 and 2.830218 (r2 =0.979) for females and 0.004032 and 3.031303 (r2 =0.974) for males, respectively. The length-at-maturity (Lm) for females and males was estimated to be 190.0 and 140.0 cm TL, respectively. Number of embryos ranged from 4 to 10 and the size at birth was estimated to range between 44.0 and 50.0 cm TL. Overall sex ratio favoured females (Female:Male = 1.73:1). There was no significant correlation between maternal TL and no. of embryos produced. Dietary analysis of stomach contents (%IRI) revealed that R. laevis fed primarily on teleosts (83.4%) and crustaceans (15.1%). This study provides the detailed biological observation on size, sex composition, lengthat-maturity (Lm), length-weight relationship and diet of R. laevis from northern Indian Ocean which can be used as essential inputs to formulate effective management plans and conservation strategies for this species in the region.

Search for the vulnerable giants: the presence of giant guitarfish and wedgefish in the Karimunjawa National Park and adjacent waters

“…The presence of other elasmobranch species with a similar or higher trophic level (TL) (R. Froese and D. Pauly, FishBase, see www.fishbase.org) in the same habitat, including the C. melanopterus (TL 3.9), H. elongata (TL 4.3), H. microstoma (TL 4.2), P. fai (TL 3.7), blotched fantail ray (Taeniurops meyeni) (TL 4.2) and U. granulatus (TL 4.1), indicates other meso-or top-predators occurring in the same sandbed habitat as G. typus (TL 3.6) and R. australiae (TL 3.5). Additionally, the presence of other predators, such as G. javanicus (TL 3.9), other piscivorous (fish eater) and durophagous (crustacean or hard-shelled invertebrate eater) moray eel species (Table S2 of the Supplementary material; Mehta 2009) and S. barracuda (TL 4.5), was also recorded at a high number (Table S2) during this study, suggesting the possibility of predatory competition with G. typus and R. australiae for similar prey items (Vaudo and Heithaus 2011;Purushottama et al 2020Purushottama et al , 2022Sreekanth et al 2022), such as crustaceans and small fishes (Hiatt and Strasburg 1960;Hansen 2015). Predatory competition may worsen a species population assumed to be depleting (Hollowell 2013), especially for G. typus and R. australiae, considering that both are Critically Endangered (IUCN Red List).…”

A diverse assemblage of Ptychodus species (Elasmobranchii: Ptychodontidae) from the Upper Cretaceous of Ukraine, with comments on possible diversification drivers during the Cenomanian

“…For example, dental cusps are absent in the dentition of extant guitarfishes (Batomorphii, Elasmobranchii), such as Rhina ancylostoma and Zapteryx exasperate (see Herman et al, 1997 ; Berkovitz and Shellis, 2017 ). Nevertheless, their un-cuspidate dental plates do not prevent these batoids from occasionally consuming small teleost fishes in addition to their main prey (e.g., crustaceans; Purushottama et al, 2022 ; Reyes-Ramíre et al, 2022 ). In elasmobranchs, variation of the “niche breadth” ( sensu Bazzi et al, 2021 ) is crucial for avoiding resource competition between predators with similar trophic adaptations, such as dental plates in batoids (see Bornatowski et al, 2014 ; Munroe et al, 2014 ; Lear et al, 2021 ).…”

Bricks, trusses and superstructures: Strategies for skeletal reinforcement in batoid fishes (rays and skates)

“…It should be noted that two of the Rhynchobatus jaws could not be confidently identified to species; although available information indicates that all Rhynchobatus species include some amount of hard-shelled prey in their diet (e.g. Darracott, 1977 ; Moazzam and Osmany, 2020 ; Purushottama et al, 2020 ). Additionally, for comparative purposes, the upper and lower jaws of the durophagous stingray Aetobatus ex.…”

“…A previous study (Dean et al, 2017) estimated Rhynchobatus jaw width to be ~7-11% of total length and our measurements from two intact Rhina specimens (95.5 and 147 cm TL) and dried jaws from six specimens from animals of known total length suggest a similar ratio (~11-15% of TL). Based on available size at maturity information for both species (Last et al, 2016;Purushottama et al, 2020), the jaw specimens used in our study (Supplementary Table S1) are likely all from mature individuals, an assertion supported by the high degree of mineralization of the skeleton (Seidel et al, 2016). It should be noted that two of the Rhynchobatus jaws could not be confidently identified to species; although available information indicates that all Rhynchobatus species include some amount of hard-shelled prey in their diet (e.g.…”