Genetic and Distribution Data of the Bramble Shark Echinorhinus brucus (Bonnaterre, 1788) and the Prickly Shark Echinorhinus cookei Pietschmann, 1928 to Better Reconstruct Their Conservation Status

Elasmobranch species show low resilience in relation to anthropogenic stressors such as fishing efforts, loss of habitats, and climate change. In this sense, the elasmobranch populations appear to be at risk of extinction in many cases. Despite conservation researchers making efforts to implement knowledge, the information on the biology, reproduction, distribution, or genetic structure of some species is still scattered, often caused by the occurrence of species in inaccessible habitats. Echinorhinus brucus is a deep benthic shark evaluated as “Endangered” on which little information is available, particularly about its geographical range and genetic structure, while E. cookei is listed as “Data Deficient”. Echinorhinus brucus belongs to the Echinorhinidae family, and its unique congeneric species is E. cookei. The main morphological diagnostic characteristic of both species is the presence of denticles with different shapes and patterns on the derma. In the present paper, mitochondrial COI and NADH2 sequences were retrieved from both E. brucus and E. cookei species, and analyses were conducted by applying different models of phylogenetic inference. Sequences of E. brucus captured in the Indian Ocean (IOS) did not cluster with the Atlantic E. brucus counterparts (AOS) but instead with E. cookei sequences; the different models showed an overlapping tree topology. Concurrently, a review of the historical and recent captures of the two species was carried out. The worldwide distribution of E. brucus excludes the Pacific Ocean area, where E. cookei occurs, and is characterised by presumably current local extinctions in the North Sea and the western Mediterranean Sea. The dataset describes two definite areas of significantly high abundance of E. brucus located in the Atlantic Ocean (Brazil) and the Indian Ocean (India). These areas suggest zones for conservation plans, especially considering the two lineages identified through molecular approaches

Focus on the Bramble Shark Echinorhinus brucus conservation status and first evaluation of possible sub-species presence

The IUCN red list is constantly updated in relation to fishing pressure and climate change and new marine species are added to it. Despite conservation researchers are working hard to implement knowledge about them, the biology, ethology, reproduction, distribution or genetic structure of many species are still scattered. Echinorhinus brucus is a deep benthic shark evaluated as endangered species on which little information is available, particularly about its genetic variability. Echinorhinus brucus belongs to the Echinorhinidae family and its sister species is Echinorhinus cookei. The main morphological diagnostic character for these two species is the presence of denticles with different shape and pattern on derma. In 2014 in the Venezuelan Caribbean Sea, a shark identified as E. brucus by genetic markers presented intermediate denticles characteristics. Some COI sequences were downloaded from Bold System and five and four sequences attributed respectively to E. brucus and E. cookei. They were aligned with ClustalW and three phylogenetic analyses were conducted. The first one was a Maximum Likelihood analysis handled with default parameters, other two were Bayesian analyses handled respectively with relaxed and strict model. Apparently, Atlantic E. brucus sequences did not cluster with Indian E. brucus sequences and all analyses showed a similar topology, supported by high value nodes (more than 85%). On the contrary, Indian sequences clustered with E. cookei sequences and ML analysis shows a small distance between them. Our results confirm how still poorly known is the variability into E. brucus species and in Echinorhinidae family. In fact, despite the few individuals sequenced and only one genetic marker available, the evolutionary history of this group is controversial, suggesting that more data should be investigated for this species