Deep Sea Species Bythaelurus stewarti Named for Shark Champion Rob Stewart

This has truly been a year of discovery for elasmobrachs! A new deepsea catshark has revealed itself to science in the Indian Ocean, and it’s name is Error Seamount Catshark (Bythaelurus stewarti). This beautiful catshark in a member of the Scyliorhinidae, which has over 158 members and it seems it just keeps growing! The discovery was made after studying 121 specimens that were collected from in 1988 and 1989 during the Russian RV ‘Vityaz’ cruise 17 as part of the largest deep sea chondrichthyan collections from the western Indian Ocean ever conducted. This study is number 20 in the “Deep-water chondrichthyan fishes of RV ‘Vityaz’ cruise 17 and other Soviet cruises in the Indian Ocean” series (Weigmann, Kaschner, & Thiel, 2018).

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Fig 2. Bythaelurus stewarti n. sp., (A) paratype, ZMH 26253, gravid female, 425 mm TL, (B) paratype, ZMH 26252, juvenile male, 340 mm TL, and (C) paratype, ZMH 26253, female embryo, 137.3 mm TL in lateral views. Scale bars: 5 cm (Weigmann, Kaschner, & Thiel, 2018).

 

These catsharks have firm, slender bodies that taper into a very narrow tail that has a pronounced upper lobe. Their snouts are long and broad with a rounded tip. The eyes are moderately sized and elongated laterally to give them a “cat eye” look that most girls would be jealous of! They do have spiracles located just behind their eyes, coupled with the lack of lower caudal lobe, this indicates they likely spend a lot of time resting on the sea floor.

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Fig 3. Bythaelurus stewarti n. sp., holotype, ZMH 26251, adult male, 425 mm TL, head in (A) lateral, (B) dorsal, and (C) ventral views. Scale bar: 5 cm (Weigmann, Kaschner, & Thiel, 2018).

 

Their upper jaws have approximately 77 diagonal rows of teeth, with the lower jaw complimenting with 74 diagonal rows. The teeth in the upper jaw have three cusps, with a larger central cusp and two smaller lateral cusplets. The lower jaw have similar teeth, however the central cusps are larger in the lower jaw.

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Fig 7. Bythaelurus stewarti n. sp., paratype, ZMH 26254, adult male, 375 mm TL, SEM images of tooth rows and single teeth. (A, B) Anterolateral teeth in upper jaw, (C, D) anterolateral teeth in lower jaw. Scale bars: (A, C) 200 μm, (B, D) 100 μm (Weigmann, Kaschner, & Thiel, 2018).

 

And just what are these little sharks munching on with the tricupidate teeth? Using radiographs and dissection, the team discovered a variety of prey items. They found the eyes, breaks, and arms of cephalopods. They also retrieved the eyes, vertebrae, and scales of teleost fishes. Many pieces of decapods were also found on the radiographs and dissections. Polychaetes, or bristle worms, were not found in dissections and were not detected in radiographs; however other deep sea catsharks are known to consume polychaetes, and 11.8% of the food material found in their stomach was unidentified.

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Fig 16. Bythaelurus stewarti n. sp., paratype, ZMH 26252, female, 295 mm TL, stomach contents. (A) partially digested teleost fish eye, (B) cephalopod eye, (C) probably a teleost bone but possibly a lophophore structure instead, (D) teleost scale, (E) beak of cephalopod Ancistrocheirus cf. lesueurii, (F) arm of cephalopod Ancistrocheirus cf. lesueurii, (G) decapod (probably brachyuran) claw, (H) antennae of a swimming decapod of the paraphyletic suborder “Natantia”, (I) antennulae of a swimming decapod of “Natantia”, (J) unidentified food remains, possibly a partially digested shrimp stomach (Weigmann, Kaschner, & Thiel, 2018).

 

This year has brought us wonderful discoveries. As we close out 2018, I think it is fitting that we honor those we have lost in the discovery of the new. On January 31st, 2017, the world lost a shark champion when we lost Rob Stewart in a diving accident. I think it is a fitting and lovely tribute to Rob in naming this species, Bythaelurus stewarti, after him. We miss you, Rob. Rob’s work and legacy lives on. Be sure to see SharkWater: Extinction.

Conservation is the preservation of life on Earth, and that, above all else, is worth fighting for. – Rob Stewart

rob-stewart

TeamSharkWater (photographer) (2016). Rob Stewart [Digital Image]. Retrieved from https://www.instagram.com/p/BHnEsSyjzw7/

To read the full open access study, please visit the link below.

The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!

Conservation legislation needs public support in order to become law and help protect the environment and wildlife. Tell your representatives that you care about environmental and wildlife conservation. It only takes a moment to make a change that will last a lifetime. Until next time finatics!

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Featured Image Source
Weigmann, Kaschner, & Thiel. (Authors). (2018). Fig 1. Bythaelurus stewarti n. sp., holotype, ZMH 26251, adult male, 425 mm TL, in lateral view [Digital Image]. Retrieved from https://doi.org/10.1371/journal.pone.0207887

Literature Cited

Weigmann S, Kaschner CJ, & Thiel R (2018) A new microendemic species of the deep-water catshark genus Bythaelurus (Carcharhiniformes, Pentanchidae) from the northwestern Indian Ocean, with investigations of its feeding ecology, generic review and identification key. PLoS ONE 13(12): e0207887. https://doi.org/10.1371/journal.pone.0207887

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