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| Leucoraja longirostris Weigmann, Stehmann, Séret & Ishihara, 2024 |
Abstract
A remarkable new deep-water skate, Leucoraja longirostris n. sp., is described based on eight specimens caught during different expeditions to the southern Madagascar Ridge in the southwestern Indian Ocean. The new species differs from all congeners by its remarkably long and acutely angled snout (horizontal preorbital length 17.2–22.6% TL vs. 8.5–11.9% TL and 4.2–6.1 vs. 1.7–3.5 times orbit length, snout angle 65–85° vs. 90–150°). Furthermore, it is apparently endemic to the Madagascar Ridge, distant from the known distribution areas of all congeners. In addition to L. fullonica and L. pristispina, L. longirostris n. sp. is also the only species with plain dorsal coloration. Furthermore, the new species is the only Leucoraja species with an external clasper component dike and, besides L. wallacei, the only one with four dorsal terminal (dt) cartilages. The shape of the accessory terminal 1 (at1) cartilage with four tips is also unique within the genus. A new approach for the visualization of the clasper characters is introduced based on 3D models of all skeletal and external features. This enables a much easier and much more precise interpretation of every single clasper component, of the entire structure, and, in particular, the relationship between external features and skeletal cartilages. A new English translation of the first diagnosis of Leucoraja is provided, along with a revised generic diagnosis and a key to the species of Leucoraja in the Indian Ocean.
Keywords: Chondrichthyes; Elasmobranchii; rough skates; systematics; taxonomy; diversity; morphology; clasper features; morphometrics; meristics
Leucoraja longirostris n. sp.
Distribution: the new species is only known from the type specimens, which were all caught on the southern end of the Madagascar Ridge at Walters Shoals at depths of 750–1050 m. The new species occurs much deeper than its western Indian Ocean congeners, which are known only at depths of 480–625 m (L. compagnoi), 484 m (L. elaineae), and 73–517 m (L. wallacei), respectively. Furthermore, the new species is the only species of Leucoraja in the western Indian Ocean known from seamounts or ridges, whereas its congeners in the area are only known from the outer continental shelf and upper continental slope.
Conclusions:
The conservation status of Leucoraja skates reveals that five of the 14 assessed species are threatened, including L. melitensis (Critically Endangered), L. circularis and L. ocellata (Endangered), L. fullonica and L. wallacei (Vulnerable), while one species (L. leucosticta) is Near Threatened, six species (L. erinacea, L. garmani, L. lentiginosa, L. naevus, L. pristispina, and L. yucatanensis) are Least Concern, and two species (L. compagnoi and L. elaineae) are Data Deficient. The recognition of a new species, Leucoraja longirostris n. sp., provides new insights into the morphological variation within the genus Leucoraja and constitutes a very unusual and remarkable addition to this skate genus. Nevertheless, the very restricted distribution of the new species raises concerns over its ability to sustain fisheries and it may be susceptible to capture in longline and, particularly, deep-water trawl fisheries. Very little information is available about fisheries operating in the area of the Madagascar Ridge, but this deep-water skate is likely unable to withstand intensive fishing pressure due to its potentially slow life history characteristics and low productivity. Walters Shoals was previously heavily fished, and this pressure may recur in the future. As fisheries targeting Orange Roughy (Hoplostethus atlanticus Collett, 1889) and Alfonsino (Beryx decadactylus Cuvier, 1829) have typically used mid-water trawls off the bottom, the new species may have a benthic refuge. However, further research is needed investigating its distribution, life history, population size and trends, and threats. This is essential for improved data collection and research, and for more effective conservation and management policy decisions.
Simon Weigmann, Matthias F. W. Stehmann, Bernard Séret and Hajime Ishihara. 2024. Description of a Remarkable New Skate Species of Leucoraja Malm, 1877 (Rajiformes, Rajidae) from the Southwestern Indian Ocean: Introducing 3D Modeling as an Innovative Tool for the Visualization of Clasper Characters. Biology. 13(6); 405. DOI: doi.org/10.3390/biology13060405
Simple Summary: Skates of the genus Leucoraja Malm, 1877, are small to medium-sized skates that usually have a short, obtusely angled snout. Until now, 14 valid species of this genus have been identified mostly in the Atlantic, but also in the Indian Ocean. In the 1970s and 1980s, a total of eight specimens of an unusual skate species were collected by researchers working on the Madagascar Ridge, an elevated area of seabed in the southwestern Indian Ocean. Despite their long snouts, the specimens could unambiguously be assigned to the genus Leucoraja due to the typical features of their claspers. Comparisons with congeners clearly indicated that these remarkable specimens represent a species new to science. It can easily be distinguished from all 14 congeners by the long and acutely pointed snout. Furthermore, it appears to occur only on the Madagascar Ridge, distant from the known distribution areas of all congeners, and shows several unique aspects in its clasper morphology. Due to the importance of the clasper features, 3D modeling is introduced as a new tool for the visualization of clasper characters. The newly described species is named Brown longnose skate.