Unveiling the Diversity and Demography of Sharks and Rays at key landing sites in Bangladesh

Abstract

In Bangladeshs marine waters in the Bay of Bengal, sharks and rays face grave threats from unsustainable fishing practices and habitat degradation. Findings from our taxonomic assessment of elasmobranchs landed at the two most important marine fish landing stations in Bangladesh bring new information and insights about the nature of the Threatened elasmobranch bycatch. This study presents findings from a taxonomic assessment at Coxs Bazar and Chattogram, two crucial landing stations in Bangladesh where most shark bycatch landings happen. Over two years, 525 fish were sampled; 206 samples were of sharks, 91 of rays, and 64 of rhino rays, representing over 29 species across 12 families. Among them are 4 families of sharks, 5 rays, and 3 rhino rays. The predominant families observed were Carcharhinidae, Glaucostegidae, and Rhinopteridae. The most frequently landed species were Sphyrna lewini, Glaucostegus younholeei, Carcharhinus leucas, Gymnura poecilura, and Mobula mobular. Out of the 525 samples, 65% (n=340) were female, 35% (n=183) were male, and the rest (n=2) were unidentified. Finding one sample of Pristis pristis indicates the severity of the decline. Additionally, for Glaucostegus granulatus, 12 among the 13 studied specimens were adult females. A significant proportion of the sampled specimens, 45%, were juveniles, while only 24% were adults. This is likely because these fishing boats bringing the catch operate in inshore water and nearshore seas, which are potential nursery grounds. The overlapping of fishing grounds and these critical habitats poses a significant challenge in elasmobranch conservation and hinders population recovery. The high number of juveniles and female adults in the catch reminds us of the necessity of integrating threatened bycatch reduction measures into the countrys fisheries management.