Marine biologists have identified a new species of the skate genus Leucoraja lurking in the depths of the Southwestern Indian Ocean.
The brown longnose skate (Leucoraja longirostris), adult male holotype in total dorsal view. Scale bar – 5 cm. Image credit: Weigmann et al., doi: 10.3390/biology13060405.
Members of the genus Leucoraja are small to medium-sized skates that usually have a short, obtusely angled snout.
Until now, 14 valid species of the genus have been identified mostly in the Atlantic, but also in the Indian Ocean.
“The 14 currently described species of Leucoraja attain maximum sizes of 30-120 cm and are found in the Indian and Atlantic oceans,” said Dr. Simon Weigmann from the Leibniz Institute for the Analysis of Biodiversity Change and his colleagues.
“Of these 12 species, only Leucoraja compagnoi and Leucoraja wallacei are also found outside of the Atlantic Ocean, i.e., in continental waters of the southwestern Indian Ocean.”
The newly-discovered Leucoraja species is the fourth known species of the genus from the western Indian Ocean.
Named Leucoraja longirostris (common name is the brown longnose skate), it is apparently endemic to the Madagascar Ridge at Walters Shoals.
“In the 1970s and 1980s, a total of eight specimens of an unusual skate species were collected at depths of 750-1050 m by researchers working on the Madagascar Ridge, an elevated area of seabed in the southwestern Indian Ocean,” the biologists said.
“Despite their long snouts, the specimens could unambiguously be assigned to the genus Leucoraja due to the typical features of their claspers.”
“It can easily be distinguished from all 14 congeners by the long and acutely pointed snout,” they said.
“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.”
The brown longnose skate (Leucoraja longirostris), adult male holotype in total ventral view. Scale bar – 5 cm. Image credit: Weigmann et al., doi: 10.3390/biology13060405.
Leucoraja longirostris is a medium-sized skate reaching at least 71.1 cm in total length.
Males mature at around 60 cm; the largest known female is 70 cm long; the smallest known specimen is the juvenile female with a 27.6 cm total length.
“The recognition of Leucoraja longirostris provides new insights into the morphological variation within the genus Leucoraja and constitutes a very unusual and remarkable addition to this skate genus,” the researchers said.
“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,” they added.
“As fisheries targeting the orange roughy (Hoplostethus atlanticus) and the alfonsino (Beryx decadactylus) 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.”
A paper reporting the discovery was published in the journal Biology.
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Simon Weigmann et al. 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: 10.3390/biology13060405