The 2014 Living Planet Report, by the Zoological Society of London and the World Wildlife Fund, the populations of mammals, birds, reptiles, amphibians and fish have declined by an average of 52%, over the 40 years from 1970 to 2010 – well on the way towards a mass extinction, which is defined as a loss of at least 75% of species.
Freshwater fish species are already suffered an average decline of 76%. The main causes have been habitat loss, pollution and invasive species. Irrigation and hydroelectric dams have also had a major impact by changing water levels and fragmenting freshwater systems.
Marine species have declined by 39% since 1970. The biggest losses have been in the tropics and the Southern Ocean. Species in decline include many types of sharks, turtles and large migratory seabirds like the wandering albatross.
There has also been a 39% decline in terrestrial species, mainly through loss of habitat to make way for human land use, particularly agriculture and urban development. Hunting and poaching also cause significant losses.
A recent report in the journal Nature indicates that 41% of all amphibians, 26% of mammal species and 13% of bird species now face extinction.
Some of the species that are critically endangered and close to extinction include the Sumatran elephant, the Amur leopard and mountain gorilla. Also endangered are species like the bonobo, bluefin tuna and loggerhead turtles.
Carbon dioxide emissions are increasing and some this is being dissolved in the oceans. As a result, seas are becoming more and more acidic and hostile to sensitive habitats.
A third of all coral reefs, which support more lifeforms than any other ecosystem on Earth, have already been lost and many marine experts believe all coral reefs could end up being wiped out before the end of the century.
Mass extinction could arrive in less than a hundred years or could take a thousand years. There is no agreement on the total number of species of animals, plants and fungi alive – estimates vary from 2 million to 50 million – while estimates of current rates of species loss vary from 500 to 36,000 species a year.
In an editorial, Nature argues that it is now imperative that governments and groups such as the International Union for Conservation of Nature begin an urgent and accurate census of numbers of species on the planet and their rates of extinction.