There are more shark and ray species in the cold seas of Russia
12.03.2021

TSU Biological Institute and Institute of Oceanology of the Russian Academy of Sciences scientists have compiled a complete annotated list of marine, brackish, and freshwater ichthyofauna of Sakhalin Island and the adjacent southern part of the Sea of Okhotsk. A large-scale analysis was carried out based on long-term research and critical analysis of literature over the past 200 years. One of the most interesting factors noted by ichthyologists is that more than 40 species of sharks and rays have been recorded in the waters of Sakhalin and adjacent waters, while the number of migrants from tropical and subtropical seas is growing. The research data was published in 2021 in the article “Annotated List of Ichthyofauna of Inland and Coastal Waters of Sakhalin Island” in the Journal of Ichthyology (Q2 Scopus).

The list compiled by scientists includes 600 species in 4 classes, 44 orders, 17 suborders, 129 families, 50 subfamilies, and 312 genera. It contains both English and Latin (scientific) names of species and information about their ranges in the Pacific Ocean and distribution in the waters of Sakhalin. The list also includes data on their conservation status, commercial value, and abundance. Modern ranges and taxonomic status are indicated for all species. According to the findings of the researchers, thermophilic species of sharks and rays, which are characterized by a completely different habitat, are increasingly appearing in the waters of the Far East.

- In recent years, in the Far Eastern waters of the Southern Kuriles and Sakhalin (the Sea of Okhotsk and the Sea of Japan and the Pacific Ocean), the capture of cartilaginous fish (sharks, rays, and chimeras), for which this habitat is uncharacteristic, has become more frequent, - says Yury Dyldin, one of the authors of the article, a scientist at TSU Biological Institute. - The reason for the migration of sharks and rays from tropical and subtropical regions is the significant warming of sea waters. Many members of this group cannot overcome the ecological boundary, and as soon as the water temperature rises, they strive to find new areas.

According to scientists, more than 40 species of sharks, rays, and chimeras have been reliably recorded in the waters of Sakhalin and adjacent waters. Among them, the flat-headed seven-gill shark (Notorynchus cepedianus), the whale shark (Rhincodon typus), the sea fox (Alopias vulpinus), and the milk shark (Rhizoprionodon acutus) can be classified as tropical and subtropical migrants. The situation of cartilaginous fish in the world now raises serious concerns among ichthyologists.

According to experts, urgent strict bans and precautionary scientifically-based catch limits are needed to prevent the death of populations of cartilaginous fish, avoid disruption of ecological functions, and facilitate the restoration of species.

- Unfortunately, people understand too late the features of the biology of the species exploited by the fishery, - notes Aleksey Orlov, a staff member at the Institute of Oceanology of the Russian Academy of Sciences and the TSU Biological Institute. - Cartilaginous species are characterized by late puberty, long life expectancy, and low growth rates and population fertility, rather than annual reproduction. All this makes them extremely vulnerable to fishing. Certain groups are exposed to special pressure: large sharks for fins, sawfish because of rostrum, which is used as souvenirs, freshwater rays for aquariums around the world, and so on.

In the CITES lists (Convention on International Trade in Endangered Species of Wild Fauna and Flora), cartilaginous species, along with sturgeons, now occupy a fairly large part of the list of fish prohibited for international trade.

- Meanwhile, the biology of these species (and there are only about a dozen of them in our Far Eastern waters) has not been studied at all, which does not allow scientifically substantiating the volumes of possible withdrawal,- notes Alexey Orlov. - Now the total allowable catch (TAC) is calculated for all skates as a single combined group, which includes both small species with a life expectancy of up to 10 years, and large ones that can live up to 15-20 years or more. Such an average approach can have a detrimental effect on the state of stocks of certain species.