By the 1940s the estimated population was down to fewer than 50 in the Russian Far East, although some hundreds still populated neighbouring China. The number increased to more than 200 in 1982, although in China there are now thought to be no more than a dozen or so Siberian tigers. Poaching has been brought under better control by frequent road inspections. Captive breeding and conservation programs are active. The Hengdaohezi Feline Breeding Centre in the northern Heilongjiang province of China,together with its partner Heilongjiang Siberian Tiger Park in Harbin , plan to release 620 Siberian tigers after its numbers have increased from 708 to 750. A 1996 count reported 430 Siberian tigers in the wild. However, Russian conservation efforts have led to a slight increase, or at least to a stable population of the subspecies, as the number of individuals in the Siberian forests was estimated to be between 431 and 529 in 2005. According to the World Wide Fund for Nature, the latest Russian Census reports put this number to be anywhere between 480 and 520 without including the small numbers of this subspecies present in mainland China.
The "Siberian Tiger Project", which has operated from Sikhote-Alin Zapovednik since 1992, found that 215 kg (474 lb) seemed to be the largest that they were able to verify, albeit from a limited number of specimens. According to modern research of wild Siberian tigers in Sikhote-Aline, an average adult male tiger (>35 months) weighs 167.3 - 185.7 kg (the average asymptotic limit, computed by use of the Michaelis-Menten formula, gives 222.3 kg for male tigers) and an adult tigress – 117.9 – 122.6 kg, respectively. The mean weight of historical Siberian tigers is supposed to be higher: 215.3-260 kg for male tigers. At least one authority suspects that this is the difference between real weights and hunter's estimates. Dale Miquelle, program director of the Siberian Tiger Project, writes that, despite repeated claims in the popular literature that the Siberian is the largest of all tigers, their measurements on more than fifty captured individuals suggest that body size is, in fact, similar to that of Bengal tigers.
Apart from its size, the Siberian tiger is differentiated from other tiger subspecies by its mane of fur around the neck, which is much more developed than in other subspecies as an adaptation against the cold. The fur of this subspecies grows longer and thicker than that of other tigers. During cold winter months, the fur can measure as long as 21 inches with 3,000 hairs over every square centimetre of its surface. The paws have extra fur to provide insulation against the snow. Siberian tigers have more white in their coats than other subspecies and coat colour is more gold than orange. Compared to other subspecies, the Siberian tiger has less striping, the stripes being more brown than black. Stripes appear largely absent on the outer area of the front legs.
Siberian tigers reach sexual maturity at 4 years of age. They mate at any time of the year. A female signals her receptiveness by leaving urine deposits and scratch marks on trees. She will spend a week with the male, during which she is receptive for three days. Gestation lasts 3–3½ months. Litter size is normally 3 or 4 cubs but there can be as many as 6. The cubs are born blind in a sheltered den and are left alone when the female leaves to hunt for food.
Cubs are divided equally between genders at birth. However, by adulthood there are usually 2 to 4 females for every male. The female cubs remain with their mothers longer, and later they establish territories close to their original ranges. Males, on the other hand, travel unaccompanied and range farther earlier in their lives, thus making them more vulnerable to poachers and other tigers.
However, it may well be that the Siberian tiger population has always shown relatively low genetic diveristy, due to a small number of founders colonising the Far East. Work with the preserved remains of the now extinct Caspian tiger (P.t. virgata) has shown that the two subspecies share a comparatively recent common history, at least when it comes to mtDNA lineages. It appears that tigers colonised central Asia at most 10,000 years ago, and the modern Siberian stock may be the result of a few Caspian tigers subsequently wandering east via northern Asia.
In areas where wolves and tigers share ranges, the two species typically display a great deal of dietary overlap, resulting in intense competition. Wolf and tiger interactions are well documented in Sikhote-Alin, which until the beginning of the 20th century, held very few wolves. It is thought by certain experts that wolf numbers increased in the region after tigers were largely eliminated during the Russian colonization in the late 1800s and early 1900s. This is corroborated by native inhabitants of the region claiming that they had no memory of wolves inhabiting Sikhote-Alin untl the 1930s, when tiger numbers decreased. Tigers depress wolf numbers, either to the point of localized extinction or to such low numbers as to make them a functionally insignificant component of the ecosystem. Wolves appear capable of escaping competitive exclusion from tigers only when human persecution decreases the latters numbers. Today wolves are considered scarce in tiger inhabited areas, being found in scattered pockets, and usually seen travelling as loners or in small groups. First hand accounts on interactions between the two species indicate that tigers occasionally chase wolves from their kills, while wolves will scavenge from tiger kills. Tigers are not known to prey on wolves, though there are four records of tigers killing wolves without consuming them. This competetive exclusion of wolves by tigers has been used by Russian conservationists to convince hunters in the Far East to tolerate the big cats, as they limit ungulate populations less than wolves, and are effective in controlling the latters numbers.
The Tungusic people considered the Siberian tiger a near-deity and often referred to it as "Grandfather" or "Old man". The Udege and Nanai called it "Amba". The Manchu considered the Siberian tiger as Hu Lin, the king.
In the early years of the Russian Civil War, both Red and White armies based in Vladivostok nearly wiped out the local Siberian tigers. In 1935, when the Manchurian Chinese were driven back across the Amur and the Ussuri, the tigers had already withdrawn from their northern and western range. The few that remained in the East Manchurian mountains were cut off from the main population by the building of railroads. Within a few years, the last viable Siberian tiger population was confined to Ussuri Land.Legal tiger hunting within the Soviet Union would continue until 1947 when it was officially prohibited. In 1962, the last tiger in Heilongjiang received protection. In the mid 1980s, it was estimated that the Siberian tiger population consisted of approximately 250 animals.
In 1987, law and order almost entirely broke down due to impending collapse of the Soviet Union. Subsequent illegal deforestation and bribery of park rangers made the poaching of Siberian tigers easier, once again putting the subspecies at risk from extinction. However due to the work of The Siberian Tiger Project, founded in 1992, the Siberian tiger has seen a steady recovery and stabilization after the disastrous post-Soviet years that saw its numbers decline sharply. The basis of the success has largely been on the meticulous research carried out on these tigers which led to the longest ongoing study of a single tiger, Olga Project Tiger #1. Through this the project was able to focus their conservation efforts to decrease tiger mortality and to improve the quality of their habitat, as well. The project included anti-poaching patrols, consultation with local governments regarding human-tiger conflicts, reducing the occurrences of clearcut logging and other habitat depletion activities.
The captive population of Siberian tiger comprises several hundred. A majority of these tigers are found in China, with other populations in Europe and North America. The large, distinctive and powerful cats are popular zoo exhibits. The Siberian tiger is bred within the Species Survival Plan (SSP), a project based on 83 wild caught tigers. According to most experts, this population is large enough to stay stable and genetically healthy. Today, approximately 160 Siberian tigers participate in the SSP, which makes it the most extensively bred tiger subspecies within the programe. There are currently no more than around 255 tigers in the tiger SSP from three different subspecies. Developed in 1982, the Species Survival Plan for the Siberian tiger is the longest running program for a tiger subspecies. It has been very fortunate and productive, and the breeding program for the Siberian tiger has actually been used as a good example when new programs have been designed to save other animal species from extinction.
The Siberian tiger is not very difficult to breed in captivity, but the possibility of survival for animals bred in captivity released into the wild is small. Conservation efforts that secure the wild population are therefore still imperative. If a captive bred Siberian tiger were to be released into the wild, it would lack the necessary hunting skills and starve to death. Captive bred tigers can also approach humans and villages, since they have learned to associate humans with feeding and lack the natural shyness of the wild tigers. In a worst-case scenario, the starving tigers could even become man-eaters. Since tigers must be taught how to hunt by their mothers when they are still cubs, a program that aimed to release captive bred Siberian tigers into the wild would face great difficulties.
In an incident at the San Francisco Zoo on 25 December 2007, a Siberian tiger named Tatiana escaped and killed one visitor, injuring two others. The animal was shot dead by the police. Whether the tiger was provoked is very much in dispute.