In late March 2015, a crabeater seal swam up the Hutt River (which flows into Wellington Harbour) and died. It was a remarkable occurrence – the crabeater seal is an Antarctic species rarely recorded in New Zealand – but no-one realised at the time that this was precisely the place in New Zealand where a crabeater seal was likely to be found.

Finding out how many crabeater seals had reached New Zealand, and where and when they had been found, turned out to be more complicated than I had expected. Birdwatchers are very good at keeping records of vagrant birds that reach New Zealand, and publishing their findings (e.g. in the journal Notornis, or the magazine New Zealand Birds, both published by Birds New Zealand), but there is no equivalent society, magazine or journal for vagrant seals.

Crabeater seals belong to the true seals, of which there are five species in the Southern Hemisphere. All five species occur in New Zealand waters, and I have listed them here in their frequency of occurrence:

• Southern elephant seal (Mirounga leonina)
• Leopard seal (Hydrurga leptonyx)
• Crabeater seal (Lobodon carcinophaga)
• Weddell seal (Leptonychotes weddellii)
• Ross seal (Ommatophoca rossii)

All five are readily distinguished from fur seals and sea lions (the most common seals seen on New Zealand coasts) by their slug-like body shape. True seals are unable to rotate their pelvis forward, and so drag their tails behind them. In contrast, fur seals and sea lions can raise their bodies off the ground and walk, gallop or climb with ease.

Elephant seals breed in small numbers on Antipodes Island and Campbell Island (both in the New Zealand subantarctic) and regularly reach mainland shores. A few pups have even been born along the east coast of the South Island and on the Wairarapa coast – most recently one at Timaru in September 2015.

The four remaining species all breed on Antarctic sea-ice, but leopard seals regularly swim north, with a few reaching New Zealand shores every year, even as far north as Northland.

The three remaining species are much rarer visitors to our shores, but it took a bit of sleuthing to discover just how rare they are. The obvious starting point was the 610 page Handbook of New Zealand Mammals (2^nd edition, published in 2005). Unfortunately the only relevant information contained therein was that “Crabeater seals are also seen occasionally in New Zealand…waters” (p.253), with no hint that Weddell seals or Ross seals ever roam so far north. The next place to check was museum holdings, which turned up three earlier crabeater seals and two Weddell seals here at Te Papa, a Weddell seal at Auckland Museum, and a crabeater seal at each of Whanganui Regional Museum and Canterbury Museum. The Department of Conservation marine mammal stranding database contained information on one animal of each species (all additional to the museum holdings). Information on two further animals (a crabeater seal and a Weddell seal) was found in old Marine Department files held by Archives New Zealand. When added to the animal found in March 2015, this produced a total of 14 verifiable records of the three species: eight crabeater seals, five Weddell seals and a single Ross seal.

The most striking feature of these 14 records is their geographical spread – or lack thereof. Eight of the animals were reported from the Wellington region (one of the Weddell seals later swam to Napier), and five of the eight crabeater seals were reported from the Hutt River or the adjacent Petone Beach.

There are at least two plausible hypotheses for the cluster of vagrant Antarctic seal records around Wellington. Maybe these seals turn up all round New Zealand, but are undiscovered, unrecognised or unreported at most sites where they come ashore. Wellington not only has a higher population density than most parts of New Zealand, but for the past century there have been scientists based at the national museum or the national offices of relevant government departments who knew how to identify the different Antarctic seals. The second theory is that as these animals were swimming north from Antarctica, the angle of the South Island directed them towards the south coast of the North Island, where they either came ashore on the south coast (Island Bay or Lyall Bay), or they swam into Wellington Harbour, where their northward passage was blocked by Petone Beach – or they could keep on swimming up the Hutt River…

Time will tell which of these hypotheses is more plausible. The ubiquitous ownership of cellphones (with cameras) plus website forums that allow images to be shared and discussed (e.g. NatureWatchNZ) means that unusual seals that turn up anywhere in New Zealand are far more likely to be correctly identified and recorded than was the case twenty or one hundred years ago.

With thanks to the Department of Conservation for permission to reproduce the first three images.

Further reading

A crabeater seal – a long way from home

Miskelly, C.M. 2015. Records of three vagrant Antarctic seal species (Family Phocidae) from New Zealand: crabeater seal (Lobodon carcinophaga), Weddell seal (Leptonychotes weddellii) and Ross seal (Ommatophoca rossii). New Zealand Journal of Marine and Freshwater Research 49: 448-461.