A delightful little pond at Orokonui Ecosanctuary is home to a mystery fish. Neville Peat reports.
No New Zealand native fish evokes as much feeling - revulsion, affection, awe, fear - as the eel.
Its snake-like head and movement and its sliminess are off-putting to many people. Yet others see fascinating if not positive traits - culinary properties, a delicacy in fact; an ancient lineage; tenacity and long life; and mysterious marine breeding grounds far from their home rivers.
To Maori, eel/tuna were coveted as a favourite and tradeable food and the inspiration for proverbs and taniwha legends.
Of New Zealand's two main species (longfin and shortfin), the longfin eel (Anguilla dieffenbachii) is the larger and longer lived (more than 60 years is not uncommon and one has been recorded at more than 100 years).
Longfins can attain a length of 1.8m and weigh more than 20kg. Stories abound of longfin eels becoming monsters. The largest ones are female.
Orokonui Stream has both species of eel and a longfin has been introduced into a pond within the ecosanctuary. Visitors sometimes spot it. Staff keep a lookout for migratory signs. They surmise the eel is female and have named her Waimarie.
The New Zealand eels are well known for their remarkable ability to slither over dry land to reach an estuary and the sea. Mostly they move under moonlight and in the past, at migration time, they have been observed congregating in writhing masses at the edge of estuaries.
As adults ready to breed, they set out on an epic journey of more than 2000km to breeding grounds in tropical Polynesia, far to the north of New Zealand. The waters around Tonga are thought to be a destination. But so far no-one has discovered exactly where they breed or filmed the phenomenon, so it remains a mystery.
Eels are rarely encountered at sea, probably because they migrate at depth. Deep ocean trenches are thought to be used for spawning, after which the adults die. The eggs develop into tiny, gelatinous, leaf-shaped larvae that drift back to New Zealand on ocean currents - an amazing feat.
On the New Zealand coast they transform into slender see-through ''glass'' eels about 60mm long, and enter the rivers in spring on flood tides under cover of darkness. A couple of weeks later they develop into young eels, called elvers. Elvers have impressive climbing skills.
On damp nights some young eels may take to land to progress up a river. They can scale waterfalls if the rocky surfaces provide enough grip. At some hydro dams, fish passes allow them to climb higher in the river system. Once in a suitable habitat, they grow into adults.
Eels are omnivores. They eat aquatic insects and other invertebrates as well as other fin fish (including trout), freshwater crayfish and even small birds, including nestlings that have fallen from nests overhanging water. Their strong sense of smell rather than beady-eyed vision allows them to find food. In colder months they may hibernate.
Longfins are grey-black to dark-brown on their upper parts with yellowish bellies. Compared to the shortfin eel the longfin's dorsal fin is longer and extends further forward than the anal fin. The mouths of longfin eels are larger.
Longfins are found only in New Zealand; shortfins, which are olive-green backed with a white belly, are found in Australia, New Caledonia, and Norfolk and Lord Howe Islands. Worldwide there are just 16 eel species.
The life history of the shortfin eel is essentially the same as that of the longfin, but shortfins are smaller and migrate at a younger average age.
New Zealand's two species are fished commercially and there is serious concern about the future of the longfins, which are said to be at risk of extinction.
Last month, the parliamentary commissioner for the environment, Dr Jan Wright, presented a report to Parliament urging a moratorium on commercial fishing, which nets about $5 million a year in export revenue. Asian markets, including Japan, are the main buyers. The average size of our eels has decreased in the era of commercial fishing. Few monsters survive.
In his 1983 book, Longfin, environmental scientist Tom Shaw presented this image of the longfin eel: ''It has a serpent's power and a snake's uncoiling grace; and the sudden appearance of a giant eel in a tiny creek, high in the hills, splashing darkly in a foot of gin-clear water is as spectacular as ... a lion's roar, or a thunder storm, or a blue whale spouting.''
Orokonui Ecosanctuary's policy is to manage its eels so that they are released beyond the predator fence when they develop physical signs that indicate migration is imminent.
Next month's Wild Ways column will describe the exceptional freshwater fish biodiversity in Orokonui Stream, with a focus on the galaxiid species, including whitebait.
Neville Peat is a trustee of Orokonui Ecosanctuary. Wild Ways appears in the Magazine section on the first Saturday of each month.
