Pacific tree frogs were introduced at Port Clements in 1964 and by the 1980's had spread all over Graham and much of Moresby Islands.
Their calls in the spring are now much a part of Islands' life but there is concern that they may be displacing the native Northwestern toad.
In 2002, the red-legged frog (picture) was also identified on the Islands.

Muskrats were released near Masset and in the Tlell area in the1920's.
Their population exploded between 1936/37 and then abruptly dropped off.
Muskrats are seldom seen now although studies indicate that their population may be increasing again. 

In 1929 and 30, 16 Rocky Mountain elk were released in Queen Charlotte City. They spread out but are mostly established in the pontoons and muskegs of Graham Island, althought there are also some on Moresby Island.
Their population appears to be stable at 40 -100 animals. They haven't increased substantially as they might have if the coastal Roosevelt elk had been introduced.

Birds have been introduced to Haida Gwaii as well. Their impacts haven't been studied extensively and most, such as the house sparrow are considered low impact.
European starlings (picture) are of more concern. Their population has increased dramatically since being introduced in the 1980's.
They are in direct competition to native berry-eating birds as well as to cavity nesting birds such as the saw-whet owl.

Feral animals are domestic animals that have gone wild. There is quite a list of feral animals on Haida Gwaii.
Pictured here are some of the cattle from the feral herd at Cape Ball. Starting with the earliest European settlers in Masset cattle have been escaping or released periodically and gone wild.
Their long term impacts include changes in plant species composition due to browsing, trampling and intensive grazing, possibly dune blowouts and the spread of weedy species.

Rabbits were let loose many times by early settlers. They don't appear to thrive on Haida Gwaii but in other places in the world, including many islands, they have been known to cause serious problems.
Cats and dogs have also gone wild. Their precise impacts haven't been studied but impacts may be surmised by their nature as predators.
Pigs and goats have also gotten free but they did not establish populations. Their impacts in many other places of the world are of serious concern.