The Chatham Islands are rich in marine mammal diversity, with five seal and 25 whale and dolphin species reported around the islands.
It is a stranding hot spot, among the top three places for strandings in New Zealand.
The New Zealand fur seal (Arctocephalus forsteri) is the most common seal species found on the Chatham Islands.
The fur seal haulouts or rookeries are located at Point Munning, Te Whakaru, Tupuangi-Moana reef, Forty Fours, The Sisters, Rangatira Island, The Pyramid, Star Keys and Eastern Reef
The four other seal species reported on the Chatham Islands are only rare or occasional visitors.
They include the New Zealand sea lion (Phocartos hookeri), with only two confirmed sightings, one on Rangatira Island in 2002 and another on Pitt Island in 2007; leopard seals (Hydrurga leptonyx), Southern elephant seals (Mirounga leonina), and subantarctic fur seals (Arctocephalus tropicalis).
Whales and dolphins
Very few sightings of whales and dolphins have been reported around the Chatham Islands, although many strandings occur.
The scarcity of sightings may be due to the low numbers of these animals, particularly whale species, as they slowly recover from the effects of decades of historical commercial whaling.
Twenty-five of the 40 whale and dolphin species recorded in New Zealand waters have been reported around the Chathams. Pilot whales (Globicephala melas), sperm whales (Physeter macrocephalus), and Gray’s beaked (Mesoplodon grayi) whales are occasionally seen, mostly around the Chatham Rise. A live southern right whale was sighted in 2003 at Owenga.
The Chatham Islands are a stranding hot spot for whales and dolphins. According to DOC's New Zealand Marine Mammal Stranding Database, nearly half of the whale strandings in New Zealand occur in Northland, Nelson and at the Chatham Islands.
Three of the most common cetaceans (dolphins, porpoises, and whales) seen around New Zealand are the common dolphin (Delphinus delphis), the dusky dolphin, (Lagenorhynchus obscurus), and the bottlenose dolphin (Tursiops truncatus) and all three periodically strand on the Chatham Islands.
A pod of three common dolphins came into shallow water in Owenga in February 2007, but were successfully turned around and guided back out to sea.
The toothed whale species that strands most commonly and in the largest numbers on the Chatham Islands is the longfinned pilot whale, otherwise known as blackfish. Since 1901 over 4000 longfinned pilot whales are reported to have stranded on the Chathams.
Strandings of this species were an important, albeit sporadic source of food and bone for the Moriori. One of the largest standings of this species, perhaps a world record, was in 1918 when 1000 whales stranded on Long Beach, Chatham Islands.
The killer whale (Orcinus orca), rarely strands on Chatham Islands beaches with only three reported strandings, including one in 1981 when 12 beached themselves at Radio Station Beach.
A Risso’s dolphin which stranded in March 2010 was the first to be reported on the Chathams. Pelorus Jack was a famous Risso’s dolphin in New Zealand, renowned for escorting ships through Cook Strait. He was a solitary social dolphin and was protected by law after an attempted assassination.
The migratory sperm whale, which occasionally ventures inshore at the Chathams is the second most common species to strand, with 24 strandings reported since 1901. In March 2000, 20 sperm whales stranded at Ngatikitiki where their skeletons remain.
Of the 12 species of beaked whale (fam. Ziphidae) in New Zealand waters, eight have been reported to strand on the Chatham Islands. Most have been Gray’s beaked whale, which was originally described by Julius von Haast from a mass stranding of about 25 whales in the Chatham Islands in the summer of 1874-75. He named it after John E Gray, a former director of the British Museum.
The spade-toothed whale, Mesoplodon traversii, is another beaked whale described from a specimen collected from Pitt Island in 1872. For well over a century it was lost in the synonomy with other species. It was resurrected as a separate species following genetics work undertaken by Anton van Helden, the marine mammal collection manager at Te Papa Tongarewa and others. Like several other beaked whales it is extremely rare, known only from three strandings in the world - on Pitt Island, White Island in New Zealand, and on Robinson Crusoe Island in the Juan Fernández archipelago.
At least six other beaked whale species have stranded on the Chatham Islands.