The average population of Arctic species rose by 16% between 1970 and 2004, however, this is not consistent across biomes, regions, and taxa.

High Arctic species populations have decreased by an average of 26% between 1970 and 2004.

Sub Arctic species populations, mostly terrestrial and freshwater species, show a recent decline since peaking in the mid-1980s, but no overall change (-3%).

Low Arctic species populations, largely dominated by marine species, have increased by an average of 46%, however, the data in the Low Arctic index is heavily biased by Eastern Bering Sea populations, many of which have experienced dramatic increases (e.g. some fish populations due to improving marine conditions and some marine mammal populations recovering from historical overharvesting).

Dramatic growth of certain populations of migratory arctic nesting geese species (as a whole almost doubling since the 1970s (from 12.5 Million to 21.4 million) shows a contrast with a steady decline in other herbivorous species, most of which are not migratory.  The increase in goose populations is thought to be largely due to increased agricultural waste in wintering grounds providing extra food resources and reduced hunting pressures.

Other Arctic grazing species have not fared as well with an overall decline of 20% between 1985 and 2004.  The reason for the decline is unknown.

Other trends, such as increasing marine fish biomass in the North Pacific, are thought to be due to recent increases in water temperatures.

Increasing marine mammal populations are very likely due to the much reduced harvest since 1970 (e.g. Sea otters, bowhead whales).

Trends in 25 North American and 21 Eurasian Caribou/Reindeer populations were investigated as part of the Index.  The total population of wild herds peaked in the early 1990s and 2000s at about 5.6 million, and have since declined by about a third overall. The largest herd in Russia, the Taimyr, peaked at around one million animals in 2000. Although recent declines are thought to be part of a natural cycle, there is growing concern about the negative impacts of climate change on Rangifer populations.  Rangifer population trends are clearly cyclical and also show striking similarities between Eurasia and North America, suggesting that there may be circumpolar factors underlying these trends.