Elasmobranchs, also known as chondrichthyans, are marine vertebrate with a cartilagenous skeleton
(Nair et al., 2015). It is one of the largest marine fish resources consisting sharks, skates, sawfishes and rays
(Kumar et al., 2022). Importantly, compared with other marine vertebrates, elasmobranchs are highly evolutionary distinct and are greatly threatened by human activities (for uses of various body parts such as the meat, fins, liver and teeth), especially by overfishing
(Pimiento et al., 2023). These fishes are distinguished from their sister group of bony fishes (teleost) by traits such as a cartilaginous skeleton, the lack of swim bladders and the presence of 5 to 7 pairs of gill slits not covered by an operculum
(Compagno, 2002). However, elasmobranchs occur regularly in low-salinity water, often beyond the tidal region. These comprise about 5% of all live elasmobranchs (approximately 60 out of 1154 described species). Although the reasons are unknown, marine elasmobranchs maintain a high requirement for urea in their bodies
(Ballantyne and Robinson, 2010). They have two groups: 1. Euryhaline elasmobranch 2. Obligate freshwater elasmobranch.
1. Euryhaline elasmobranch
Those fishes that can tolerate a wide range of salinities, from freshwater to brackish, are termed ‘euryhaline elasmobranch’. Euryhaline chondrichthyans include sawfishes (Pristidae), several whaler sharks (Carcharhinidae), one skate (Rajidae) and several stingrays (Dasyatidae), which are primarily marine fishes that can enter and stay in freshwater
(Lucifora et al., 2015).
2. Obligate freshwater elasmobranch
These fishes confine to freshwater and comprise all the freshwater stingrays (family-Potamotrygonidae) and several stingrays (Dasyatidae), which complete their whole life, cycle exclusively in freshwater
(Lucifora et al., 2015).
According to the IUCN, freshwater elasmobranchs are typically at high risk of extinction but least evaluated. The IUCN Red List of Threatened Species is increasingly used to reveal the health of ocean biodiversity.
Dulvy et al., (2021) assessed 1,199 chondrichthyans and demonstrated the need for fishing limits on target and incidental catch and spatial protection to avoid further extinctions and allow for food security and ecosystem functions.
Highlights
1. More than one-third of chondrichthyan fish species are threatened by overfishing.
2. A disproportionate threat in the tropics risks the loss of ecosystem functions and services.
3. Three species not seen in >80 years are Critically Endangered (Possibly Extinct).
4. The depletion of these species has a continuous demand for human food.
Diversity distribution of freshwater elasmobranches in the world
According to IUCN, 1,199 species were reported in Class Chondrichthyes-sharks, rays and chimeras
(Dulvy et al., 2021). The first global assessment (2014) concluded that one-quarter (24%) of species were threatened. Now, 391 (32.6%) species are threatened with extinction.
The seven freshwater obligate chondrichthyans comprised a single West African species (Smooth Stingray-
Fontitry gongaurouensis) and six Southeast Asian species (Roughback-Whipray
Fluvitry gonkittipongi, Marbled Whipray-
F.
oxyrhynchus, White-edge Whipray-
F.
signifer, Mekong Stingray-
Hemitry gonlaosensis, Chindwin Cowtail Ray-
Makararaja chindwinensis and Giant Freshwater- Whipray (
Urogymn uspolylepis).
Distribution and freshwater elasmobranches in India
Indian waters support a diverse chondrichthyan group consisting of more than 110 species of elasmobranch, which comprises 66 species of sharks and 44 species of batoides
(Raje et al., 2002). Later description of new records and new species may bring to this sum to about 150-170 species from the Indian coast only, of which 3% are Critically Endangered (CR), 5% are Endangered (EN), 26% are Vulnerable (VU), 21% are Near Threatened (NT), 8% are of Least Concern (LC), 27% are Data Deficient (DD) and 10% are Not Evaluated (NE)
(Joshi, 2022;
IUCN, 2024). However, there is no correct information on freshwater elasmobranchs.
In the present report, we have listed 13 species belonging to 3 orders, 3 families and 10 genera from secondary data. We assessed the IUCN status also (Table 1) and provide a systematic checklist of Indian freshwater elasmobranches with their taxonomic position, distribution and IUCN Red List status (Table 2).
Habit and habitats
The freshwater elasmobranches occupy a wide range of habitats, including freshwater riverine (but not land-locked water systems) and lake systems, inshore estuaries and lagoons, coastal waters, the open sea and the deep ocean. Most elasmobranchs are mid-level or top predators and play a key role in trophic food webs
(Yeldan, 2018).
Socio-economic significance of elasmobranch
Chondrichthyans groups are one of the most versatile/ valuable fisheries resources, providing meat and shark fins for human consumption (Shark fin soup); gills (as a tonic), leather (Purse, belt); shark liver oil used to produce lubricants, for medicine, fuel, cosmetics and vitamin A; live specimens for aquaria; and shark teeth (Ornamental) and jaws sold as tourist curios (Fig 1)
(Dent and Clarke, 2015). More recently, shark cartilage has been exploited to treat cancer and other ailments and sharks and rays have become an attraction to scuba divers.
Major emerging threats to elasmobranches
Threats posed to elasmobranchs habitats by humans are directly proportional to the habitat’s proximity to land. Elasmobranch fishes (sharks, rays and skates) face several major emerging threats to their survival and well-being (Fig 2)
(Bornatowski et al., 2014). These threats contribute to declining populations and endanger many species. Some of the emerging threats to elasmobranchs are:
Overfishing
It is one of the threats to elasmobranchs driven by the demand for shark fins, meat and other products. They are caught by bottom trawls, longlines and gillnet fishing gears
(Dulvy et al., 2021). Many species have slow growth rates and reproduce infrequently, making them particularly vulnerable to overexploitation.
By-catch
Elasmobranchs are often caught unintentionally as by catch in commercial fishing operations targeting other species. It can lead to high mortality rates for elasmobranchs, especially when discarded at sea.
Habitat loss
Habitat degradation and loss, primarily caused by coastal development, pollution and climate change, impact elasmobranchs’ breeding and feeding grounds. Mangroves, estuaries and coral reefs are crucial habitats for many species.
Climate change
Climate change poses several threats to elasmobranchs. Rising ocean temperatures can alter their distribution and affect prey availability. Ocean acidification can harm their calcium-based skeletons and eggs and changing currents can impact migration patterns.
Illegal fishing
Illegal, unreported and unregulated (IUU) fishing operations often target elasmobranchs for their valuable fins and meat. These activities can undermine conservation efforts and exacerbate population declines.
Trade and shark finning
The global trade in shark fins for use in shark fin soup and traditional medicines is a cause of elasmobranch exploitation. Shark finning, the practice of removing fins and discarding the rest of the carcass at sea, is wasteful and unsustainable.
Shark mislabeling
Shark mislabeling refers to the fraudulent practice of misidentifying or misrepresenting shark species in the seafood supply chain. It can occur at various stages, including fishing, processing and distribution. The mislabeling of shark products has consequences for consumers and the marine environment
(Bornatowski et al., 2013).
Pollution
Pollution from plastic debris, chemical pollutants and heavy metals can harm elasmobranchs directly or indirectly by contaminating their prey and habitats.
Invasive species
Invasive species introduction in freshwater habitats can disrupt elasmobranchs’ ecosystems and reduce prey availability.
Lack of conservation measures
Many elasmobranch species lack adequate protection under national and international conservation agreements. Stronger regulations and enforcement are needed to safeguard these animals
(Fischer et al., 2012).
Scientific knowledge gaps
Limited scientific understanding of elasmobranch biology, population dynamics and behavior can hinder conservation efforts. More research is needed to fill these knowledge gaps.
Conservation status of Indian freshwater elasmobranches
International conservation and management initiatives for elasmobranches fish
● United Nations Convention on the Law of the Sea (UNCLOS), 1982.
● UN Fish Stocks Agreement, 1995.
● FAO Code of Conduct for Responsible Fisheries (CCRF),1995.
● Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), 1973.
● Convention on Migratory Species (Bonn Convention), 1979.
● Convention on Biological Diversity, 1992.
● The International Union for Conservation of Nature.
In 2013, the Ministry of Environment and Forests, Government of India implemented shark finning. The Indian Wildlife (Protection) Act, 1972 lists ten elasmobranchs in Schedule I part 2(A) in MoEF, 2001, which are identified accurately in the field to ensure their protection (Table 3).
