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Worldwide, Mexico is well-known for a lot of things: its cuisine, tequila, mariachis, pyramids, and beaches, as well as being the country with the most Spanish-speaking residents (more than 120 million people).
In contrast, however, little is known for the country’s chondrichthyan fauna: a class of fishes containing the sharks, chimaeras, rays, and skates.
To fill the gap in the knowledge of the Mexican marine fauna, scientists from the Instituto Politécnico Nacional – Centro Interdisciplinario de Ciencias Marinas (IPN-CICIMAR) conducted a multidisciplinary study on the extant species of the country’s Economic Exclusive Zone (EEZ) and, as a result, reported a total of 217 extant chondrichthyan species. Their findings are published in the open access journal ZooKeys.
In their updated taxonomic list, the team of Dr. José De La Cruz-Agüero, Dr. Jorge Guillermo Chollet-Villalpando, and Venezuelan graduate students Lorem González-González and Nicolás R. Ehemann report eight chimaeras, 111 sharks and 98 ray and skate species. These numbers equate to 18% of the world’s chondrichthyans.
Split between the Mexican coasts there are 92 species recorded from the Mexican Pacific and the Gulf of California, whereas 94 fishes are identified for the Gulf of Mexico and the Caribbean Sea. Additionally, 31 species are known from both coasts.
“The species richness will undoubtedly continue to increase, due to the current investigations in progress, as well as the exploration of deep-water fishing areas in the EEZ,” comment the scientists.
Considered to be primitive fishes, sharks, skates, chimaeras, and rays are believed to have been inhabiting the planet for the last 420-450 million years. To put it in perspective, the earliest evidence of our species – Homo sapiens – is pretty ‘young’ at 315,000 years.
Not only do these species are peculiar with their lack of a bony skeleton when compared to the more recently evolved fishes, but they also have an unusual digestive system, featuring a spiral valve, where the lower intestine is twisted like a corkscrew to increase the surface area. They don’t have a swimming bladder either. Further, there are about 650 extant species, whereas the known bony fishes are estimated to be over 35,000.
Most of the chondrichthyans are considered either ‘Critically Endangered’ (a classification a step below ‘Extinct’) or ‘Endangered’, according to the Red List of the International Union for Conservation of Nature (IUCN). The majority are also featured in the Convention on International Trade in Endangered Species.
As if to make matters worse, these fishes are also particularly susceptible to overfishing and have a low rate of growth and fecundity (females give birth to between 1 and 25 pups a year).
Original source:
Ehemann NR, González-González LV, Chollet-Villalpando JG, Cruz-Agüero JDL (2018) Updated checklist of the extant Chondrichthyes within the Exclusive Economic Zone of Mexico. ZooKeys 774: 17-39. https://doi.org/10.3897/zookeys.774.25028