The Minnesota Zoo, Home of the AZA Tiger Species Survival Plan®

Since its beginning, the Minnesota Zoo has provided leadership in tiger conservation. Shortly after the Minnesota Zoo was born, the first Species Survival Plan (SSP®), the Tiger SSP, was developed by Dr. Ulysses Seal. He was responsible for creating the first steps of a scientific approach to the management of an endangered species in captivity, using the tiger as a model. Today most of the zoos of the world follow a similar plan for the management of many of their endangered species.

What is an SSP?

The Species Survival Plan, or SSP, began in 1981 as a cooperative population management and conservation program for selected species at North American zoos and aquariums. Each SSP manages the breeding of a species to maintain a genetically and demographically healthy, self-sustaining captive population. SSPs include other conservation activities such as research, education, reintroduction, and field projects. Currently, 104 SSPs covering 147 individual species are administered by the Association of Zoos and Aquariums (AZA).

Minnesota Zoo and the Tiger SSP

The Tiger SSP began as a management program for Amur tigers in captivity which is the subspecies of tiger we have at the Minnesota Zoo. Dr. Seal coordinated this plan until 1987 when he became Tiger SSP coordinator for all tiger subspecies managed in North America including the Amur tiger, the Sumatran tiger, and the Indochinese tiger.
Dr. Ron Tilson, current Conservation Director at the Minnesota Zoo and one of the world's leading tiger experts, took over as Amur tiger coordinator in 1987 and since 1992 has served as both the Tiger SSP coordinator which oversees all three subspecies and the Amur tiger SSP Coordinator.

What does an SSP Coordinator do?

An SSP coordinator is responsible for managing a population of an endangered species to insure it remains genetically healthy and stable as an insurance policy in case something happens to the wild population. This is accomplished with the help of a studbook keeper for each species or subspecies in the SSP who maintains information about each animal's family history, breeding history, age and location. The studbook keeper for the Amur and Indochinese tiger subspecies is Kathy Traylor-Holzer, registrar and population analyst at the Minnesota Zoo. With the studbook information, an SSP coordinator can make recommendations with the help of other advisors about which animals should breed with which other animals. Often these recommendations require tigers to be moved to zoos in other parts of the country and sometimes other parts of the world.
Since the zoo opened, we have had 41 tiger cubs born here at the zoo. We have sent tigers to 26 different zoos in the U.S. and around the world and have received tigers from 18 different institutions around the world. Through his work in captivity with the Tiger SSP and his fieldwork helping to save wild tigers in Sumatra and China, Dr. Tilson and the Minnesota Zoo are making a difference in the conservation of this highly endangered species.

Report on Tiger SSP Status (2002)

Introduction
Three of five Panthera tigris subspecies (P.t. altaica, P.t. corbetti, and P.t. sumatrae) are currently managed by the AZA Tiger SSP. The Amur (Siberian) tiger population will be managed at the current level of 150 tigers, and each of the other two subspecies, Sumatran and Indochinese, will be expanded up to a maximum of 150 tigers each. All subspecies will be managed to maximize the retention of gene diversity, but it is recognized that it may not be feasible to maintain 90% gene diversity over a 100-year program without substantial founder importation, particularly for the Sumatran and Indochinese subspecies. For future years the Tiger SSP may need to consider the option of managing only two subspecies, one temperate (Amur) and one tropical (Sumatran or Indochinese), depending on our ability to reach program goals and the feasibility of acquiring sufficient founders.

Data Tables (current through 1 March 2002)

Current Population Status
The Tiger SSP currently manages three tiger subspecies - the Amur tiger (Panthera tigris altaica), Sumatran tiger (P.t. sumatrae) and Indochinese tiger (P.t. corbetti). As of March 2002 there are 87 SSP member institutions holding 266 tigers: 149 Amur tigers (56%); 55 Sumatran tigers (21%); 37 Indochinese tigers (14%); and about 25 generic tigers (9%). For the present, the Tiger SSP plans to expand the captive tiger population to eventually fill the 450 spaces suggested by the AZA Felid Taxon Advisory Group, allotting 150 spaces to each subspecies. The Amur tiger population will be held stable at approximately 150 tigers, while the Sumatran and Indochinese tiger populations will be expanded

The current Amur tiger SSP population stands at 149 individuals derived from 57 founders and retaining 96.7% gene diversity. This captive population has a stable age structure and good reproductive success.

Wild Amur tigers are found primarily in two populations in the Russian Far East and at least one or more populations on the Russia-China border and into northeast China. Estimates are about 400 wild adult tigers. This subspecies is considered critically endangered by the IUCN/SSC Cat Specialist Group and, like all five tiger subspecies, is threatened primarily by habitat loss and fragmentation. Poaching pressure apparently has declined recently due to intensive anti-poaching activities.

The Sumatran tiger SSP population consists of 55 individuals derived from 16 founders and retaining 91.3% gene diversity. A breeding moratorium was under effect from 1994-1997 pending the results of DNA testing to verify subspecies purity, resulting in a gap in the population's age structure. Importations of Sumatran tigers from Indonesia are being pursued to promote the genetic basis of this population.

There are an estimated 400 wild Sumatran tigers living primarily within six national parks and possibly within a few other protected areas of Sumatra. This subspecies is also considered critically endangered by the IUCN/SSC Cat Specialist Group. In the past year field reports suggest that available habitat is under severe pressure from squatters and lumber extraction, fragmentation is increasing and poaching pressure is at an all-time high.

The Indochinese tiger SSP population is now at 37 tigers maintained in 14 institutions. This population is based upon only four founders and currently retains 80.8% gene diversity. The importation of new founders is critical to the viability of this program and needs to be actively pursued.

Wild Indochinese tigers live in small isolated subpopulations throughout mainland Southeast Asia and are estimated to number about 1,200-1,800. Indochinese tigers are considered endangered by the IUCN/SSC Cat Specialist Group. Many of these populations are fragmented, poaching is intense, and optimal habitat is decreasing. A recent field report from Cambodia describes a newly discovered population inhabiting a vast relatively undisturbed forest.

Demographic Trends
The Amur tiger population has been managed at about 150-160 animals over the past 15 years to allow newly available spaces to be used for the other two tiger subspecies. Generation time for this stable population is 8.2 years, sex ratios at birth are equal, and the average litter size is 2.5 cubs. Mortality prior to reproductive age is about 40%. The Sumatran tiger population has been fairly static at 55-60 since the breeding moratorium despite the resumption of breeding in 1997. This population is becoming demographically insecure as the majority of the breeders age. Concerted efforts are being made to increase reproductive success so that the population can be expanded and made demographically viable. The Indochinese tiger population has grown dramatically from 10 to 37 individuals since population expansion was approved in 1998 resulting in a young age structure. Demographic parameters for Sumatran and Indochinese tigers are similar to those for Amur tigers, except that mean litter size is larger (3.0 cubs) and generation time is shorter (5.8 years) for Indochinese tigers.

Population Genetics
Gene drop analyses of the Amur managed population indicate that 96.7% of the gene diversity has been retained in the population, representing 15.22 founder genome equivalents (FGE) from 57 founders. Gene diversity has gradually increased for the past 20 years due to population management and the periodic incorporation of new genetic founders from Europe and Russia. Current inbreeding levels are relatively low (mean F = 0.008). Genetic analyses of the Sumatran population indicates that 91.3% of the gene diversity has been retained. Sixteen founders (5.74 FGE) are represented in the population. Inbreeding is becoming more prevalent (mean F = 0.035), and new founders will be needed to maintain 90% gene diversity. The Indochinese tiger population has retained 80.8% gene diversity (FGE = 2.68) and is descended from four founders. All potential breeders are now related, and inbreeding will quickly increase from its current level (mean F = 0.079) without genetic supplementation. Recruitment of new founder stock for the Sumatran and Indochinese tiger programs is a high priority and will be essential for the viability of these SSP populations.