Elasmobranchs are among the most endangered vertebrates, with around 25% of species now threatened with extinction. However, effective conservation is being hindered by taxonomic confusion; the high levels of morphological similarities among living organisms mean it is difficult to classify elasmobranchs into accurate species groupings. DNA sequencing technologies have even identified ‘cryptic’ species within this group (species that look alike but are genetically distinct). More new species are being described in recent decades than ever before thanks to these technologies, this article names just a few of my favourites…
1. Carolina hammerhead
The scalloped hammerhead (Sphyrnalewini) is an abundant coastal shark found in the warm temperate and tropical waters of the Atlantic, Indian and Pacific Oceans. Genetic evidence recently confirmed the coexistence of two discrete lineages (S. lewini and a cryptic, unnamed species) in the western north Atlantic, which was later corroborated with vertebral counts for both species. In a more recent study it was shown that this cryptic species was also found in the western South Atlantic Ocean, extending its distribution (Pinhal et al., 2012). This cryptic hammerhead has now been formally described as the Carolina hammerhead, Sphyrna gilberti sp. nov (Quattro et al., 2013)!
Above: Scalloped hammerhead. IUCN red list: vulnerable.
2. The spotted eagle ray complex
The spotted eagle ray (Aetobatus narinari) is a large, reef-associated, and mainly coastal elasmobranch, occuring throughout the tropics. Although currently designated a single, vulnerable species throughout its range, geographic differences in its morphology and parasite evolution suggest the presence of cryptic speciation. Recent genetic evidence supports just that; one species is thought to have a range extending through the Western and Central Pacific and the other throughout the Central Atlantic and the Eastern Pacific. As a single species, A. narinari was thought to be circumglobal; these reduced ranges and population sizes for each species therefore reinforce concerns about the already threatened and vulnerable status of these batoid fish (Richards et al., 2009).
Above: Spotted eagle ray. IUCN red list: vulnerable.
3. Blue skate/ Flapper skate
The common skate, Dipturus batis (L. 1758) is the largest of the batoid (skates and rays) fishes growing up to 3m in size! It’s also one of the most vulnerable, now classified as critically endangered on the IUCN red list (Dulvy et al., 2006). Once abundant in the north east Atlantic, this species’ former range is thought to have stretched from Iceland and northern Norway, through to Madeira and northern Morocco, including in the Mediterranean Sea and throughout the waters of the British Isles. Now, D. batis appears to be absent from most of its former range and is the first fish to have been formally described as locally extinct across part of its range (Brander, 1981; Dulvy & Reynolds, 2002).
Recent work on D. batis suggested that the North-eastern Atlantic common skate is actually two new species: the larger growing flapper skate (Dipturus cf. intermedia) and the smaller blue skate (Dipturus cf. flossada) (Griffiths et al., 2010; Iglésias et al., 2010). These results have serious implications for the conservation status of the ‘common skate’, as it is likely that the extinction risk of the flapper skate and blue skate is significantly higher than previous estimates that treated D. batis as a single species. However, more research needs to be conducted in order to understand the scale of their declines.
Above: the Flapper skate, the largest fish to ever be caught in the UK, weighing 208lbs! Image source: https://www.dailymail.co.uk/news/article-2701218/The-one-got-weigh-Biggest-fish-caught-Britains-shores-heavier-gorilla.html. IUCN red list: critically endangered.
4. Oceanic manta/ Reef manta
‘Manta ray’ has historically referred to just one circumglobal species, the giant manta ray Manata birostris. However, it has recently been discovered that ‘manta ray’ actually represents two genetically distinct species: the oceanic (Manta birostris) and the reef manta (Manta alfredi) (Marshall et al., 2009). These two species differ in their morphology and have been found to inhabit different areas of the ocean. The smaller reef manta, which grows up to 5m in width, is found nearer to the coast and is often seen by humans. The oceanic manta, on the other hand, can reach up to 7 m in size and is thought to be more wide-ranging, inhabiting the pelagic ocean and migrating larger distances.
In addition to these two currently recognised species, a putative third species of manta ray has also been hypothesised and is thought to reside in the Atlantic. However, more research is required to confirm its existence as a novel species (Marshall et al., 2009; Hinojosa-Alvarez et al., 2016; Stewart et al., 2018).
Above: different morphologies of oceanic and reef mantas. Image source: http://micronesianconservation.org/manta-biology/. IUCN red list: vulnerable.
Why do we care about cryptic speciation?
Cryptic speciation in elasmobranchs causes a lot of taxonomic confusion, meaning it’s not clear which organisms belong to which species. This makes it difficult to assess their population declines, habitat use, habitat ranges and, ultimately their conservation status. Hence, knowing which areas to protect and implementing effective management plans remains a difficult task. Given the vulnerable status of sharks, rays and skates worldwide more research is needed to accurately assess species status so we can conserve these beautiful creatures.
Griffiths et al. (2010). Molecular markers reveal spatially segregated cryptic species in a critically endangered fish, the common skate (Dipturus batis). Proceedings. Biological sciences / The Royal Society, 277(1687), 1497–1503.
Hinojosa-Alvarez, et al. (2016). A potential third Manta Ray species near the Yucatán Peninsula? evidence for a recently diverged and novel genetic Manta group from the Gulf of Mexico. PeerJ 4:e2586. doi: 10.7717/peerj.2586
Iglésias et al. (2010). Taxonomic confusion and market mislabelling of threatened skates: important consequences for their conservation status. Aquatic conservation: marine and freshwater ecosystems, 20(3), 319–333.
Marshall, et al. (2009). Redescription of 1187
the genus Manta with resurrection of Manta alfredi (Krefft, 1868) 1188
(Chondrichthyes; Myliobatoidei; Mobulidae). Zootaxa 2301, 1–2
Pinhal et al. (2012) Cryptic hammerhead shark lineage occurrence in the Western South Atlantic revealed by DNA analysis. Marine Biology. 159:829-836. hps://doi.org/10.1007/s00227-011-1858-5
Quattro et al. (2013). “Sphyrna gilberti sp. Nov., a new hammerhead shark (Carcharhiniformes, Sphyrnidae) from the western Atlantic Ocean”. Zootaxa. 3702 (2): 159.
Richards et al. (2009). Species Delineation and Evolutionary History of the Globally Distributed Spotted Eagle Ray (Aetobatus narinari). Journal of Heredity, 100(3); 273–283,
Stewart et al. (2018). Important juvenile manta ray habitat at flower garden banks national marine sanctuary in the northwestern Gulf of Mexico. Mar. Biol. 165:111. doi: 10.1007/s00227-018-3364-5