Kaluga sturgeon, or simply Kaluga, (Huso dauricus) is endemic to the Amur-Heilong River. The Zeya-Bureya population is listed in Russia’s Red Book under category 1 as a “disappearing population of an endemic species.” The species listed as Endangered in the IUCN Red List of 2004 and trade in kaluga is restricted by listing the species in CITES Appendix 2.
It was formerly believed that kaluga was strictly a freshwater fish. However, it is now known that young fish (up to 30-50 kg) inhabit marine waters from the northern Sea of Okhotsk to Hokkaido Island. Fishermen also report catching kaluga in the Magadan region. Kaluga is caught in the north of Khabarovsky Krai and off Sakhalin Island. Young kaluga are found in rivers of southern Primorsky Province.
Most kaluga inhabit the brackish bay at the mouth of the Amur-Heilong and the eastern part of Sakhalin Gulf. Here, kaluga feed on pink and chum salmon, spawning herring, and smelt. Other prey includes marine fish, shrimps, and freshwater fish.The freshwater range of kaluga is similar to that of the Amur sturgeon (Accipenser schrenkii) and stretches for several thousand kilometers into the Amur-Heilong basin. The kaluga range includes the rivers Shilka, Onon, Zeya, Bureya, Songhua, Ussuri-Wusuli (and Khanka-Xingkai Lake), and Amgun. Kaluga is now virtually extinct in the Argun, Songhua and Ussuri-Wusuli Rivers due to overfishing in those rivers and water pollution in the Songhua and Argun.
The spawning range of kaluga is also similar to that of Amur sturgeon and its upstream range limit is not yet known. According to the Heilongjiang Province Department of Fisheries, mature kaluga do not go upstream farther than Blagoveshensk/Heihe. However sightings and catches of mature fish were reported in Amur-Heilong tributaries in the Chita region all the way upstream to the Onon River during 2002-2003.
Kaluga is one of the world’s largest freshwater fish, reaching a length of 5.6 meters and a weight of 1,140 kg. Females mature at 16-17 years of age, when their total length is over 2 meters. Males mature one or two years earlier than females. The life span of kaluga is believed to be 48-55 years. Spawning occurs in gravel and sandy river beds at depths of three to seven meters. Spawning season begins in May and lasts through June. Fecundity may reach 4 million eggs. Fry are carried downstream in the current. Kaluga is a predatory species whose diet includes conspecifics. Spawning migration (at least the first) may be 1,000 km or more.
Various sources reported in 2000-01 that large maturing Kaluga sturgeon (age over 13 years, length over 180 cm, and weight at least 50 kg) numbered at least 60,000 fish with a total biomass of 5.5 thousand tons (at an average weight of 90 kg). During recent years a rapid decline in abundance has been reported. By some estimates, existing levels of official catch and poaching could represent up to 95% of the spawning population annually. At this rate, the number of mature fish in 2010 could be one tenth that of 2000. The main causes for decline are the same as for Amur sturgeon – licensed fishing in China and poaching in Russia. In China the Amur-Heilong population of Kaluga and Amur sturgeon is the main source of fry for farming sturgeon for meat in southern regions. Water pollution is almost certainly negatively affecting kaluga sturgeon reproduction, both the chronic levels of toxic compounds and the acute concentrations caused by accidental and intentional discharges in 2005 and 2006.
The trend in the kaluga sturgeon population may be the best demonstration of the impossibility of protecting Amur-Heilong
biodiversity through unilateral efforts. Unless an effective joint Russia-China program of sturgeon
conservation is implemented in the near future the commercial fisheries (legal or not) are doomed and the species might face extinction.
Dead Kaluga sturgeon. Schastia Bay near Amur river mouth. (Photo by Aleksey Antonov)