Sakhalin Sturgeon (Acipenser (Sinosturio) mikadoi)

Adult Sakhalin sturgeons (Acipenser mikadoi - Sinosturio mikadoi) that came to the Tumnin river for spawning. The lower stream of the Tumnin river, approximately 10 km upstream from the village of Datta, the port of Vanino district, Khabarovsk region, the Russian Far East, June 2008. The Russian Federal Agency for Fishery staff members Victor Khrisanfov (Moscow), Konstantin Yafarkin (Vanino).
On Google Maps: https://www.google.ru/maps/@49.2812022,140.2280037,2130m/data=!3m1!1e3?entry=ttu&g_ep=EgoyMDI2MDMxMC4wIKXMDSoASAFQAw%3D%3D

A juvenile Sakhalin sturgeon (Acipenser mikadoi - Sinosturio mikadoi) which lives in the lower stream of the Tumnin river and has not yet changed the river for marine habitat. The lower stream of the Tumnin river, approximately 10 km upstream from the village of Datta, the port of Vanino district, Khabarovsk region, the Russian Far East, June 2008.

On Google Maps: https://www.google.ru/maps/@49.2812022,140.2280037,2130m/data=!3m1!1e3?entry=ttu&g_ep=EgoyMDI2MDMxMC4wIKXMDSoASAFQAw%3D%3D

Sakhalin sturgeon (Acipenser mikadoi, according to the latest taxonomic version Sinosturio mikadoi) is one of the most unusual sturgeons of the world fauna and probably the rarest sturgeon of the Russian fauna. It is found in the northwestern Pacific (the Sea of Okhotsk, the Strait of Tartary, the Sea of Japan), and goes to spawn in relatively large rivers with special estuary zones characterized by rather long sections from the mouth of the river upstream reached by salted marine water flowing along the bottom of the river during the high tide period. In such sections there is an extensive food base for young sturgeons, who live there up to four years before leaving the river and going into the sea. Sakhalin sturgeon does not appear to go for spawning particularly high upstream, although its exact spawning sites are unknown. The movement of juvenile sturgeons from fresh water to marine, their adaptation to a new habitat, to a new food base is taking place gradually. Right after releasing itself from the egg envelope the larva of Sakhalin sturgeon, instinctively hides under the stones not to be swept away by the rapid flow into the salty section of the river. This is what we observe in the larvae-keeping tanks: the larvae stay in shelters (such as under rocks) and does not come out to search for food, but eats only what comes under rocks. In this way, its behavior is fundamentally different from that of the larvae of other sturgeons of Russian fauna, which spawn in rivers with a more calm flow and at greater distances from the mouth: in the larvae-keeping tanks, they swim actively in search of food.

Previously, Sakhalin sturgeon probably spawned in several rivers in Khabarovsk Region (a region in the Russian Far East), Sakhalin Island (where the Sakhalin sturgeon may still be spawning in the Viakhtu river), and possibly also in Primorsky Region (a region in the Russian Far East) and Japan. However, today the only reliable spawning site of the Sakhalin sturgeon is the Tumnin river, which originates in the mountains of Sikhote-Alin’ and flows into the Strait of Tartary (the village of Datta surroundings in several kilometers from the port of Vanino). For unclear reasons, the number of Sakhalin sturgeons has steadily decreased over the past 20 years. Even in the Tumnin river, where mature Sakhalin sturgeons spawn from late May to mid-June, experienced local fishermen working in cooperation with the Russian Federal Agency for Fishery staff members and a team of enthusiasts have been unable to catch more than one-two fish that came to Tumnin for spawning. Information from the people living in the villages located in the lower stream of the Tumnin river, as well as data from ichthyologists, show that Sakhalin sturgeon is on the verge of extinction. Under such circumstances, the only viable way to prevent loss of Sakhalin sturgeon is to create its reserve brood stocks in the sturgeon hatcheries, reproduce and release juvenile sturgeons into wild in the lower stream of the Tumnin river. The task of observing the spawning sites of Sakhalin sturgeon in the lower stream of the Tumnin river is not realistic at present, as exact locations of the spawning sites are unknown and there is no research program to find them. We also do not know whether Sakhalin sturgeon have any problems during its life at sea. Poaching in the Tumnin river and incidental by-catches at sea may play a role, but the problem does not seem to be limited to poaching. To a certain extent the problem may be exacerbated by Polypodium parasites (Cnidaria) sometimes found in the Sakhalin sturgeon eggs.

The lower stream of the Tumnin river (the only reliable spawning site of the Sakhalin sturgeon nowadays) on Google Maps: https://www.google.ru/maps/@49.2983147,140.2724718,10654m/data=!3m1!1e3?entry=ttu&g_ep=EgoyMDI2MDMxMC4wIKXMDSoASAFQAw%3D%3D

Some related links:

Sakhalin sturgeon in the IUCN Red List: https://www.iucnredlist.org/species/241/227578157

Sakhalin sturgeon in Fishbase: https://www.fishbase.se/Summary/Acipenser-mikadoi

Sakhalin sturgeon in iNaturalist: https://www.inaturalist.org/taxa/1633194-Sinosturio-mikadoi