The Short-finned Eel
Written by Ragan Mason (Lincoln University)
Edited by Michael Hudson, Lincoln University, September 2006
- Scientific name: Anguilla australis subspecies australis
- Popular Common names: Short-finned Eel, tuna
- Other common names: ‘silverbelly’, tuere, pia, tuna harakeke, koroamo
- Kingdom: Animalia
- Phylum: Chordata
- Class: Actinopterygii (ray finned fishes)
- Order: Anguilliformes (eels and morays)
- Family: Anguillidae (the freshwater eels)
- New Zealand Status: native
- Taxonomy sources: McDowall (1978).
Like most eels, the short-finned eel is long and of tubular shape. It has a small, narrow head, small eyes, and a mouth that extends to just below the eyes; but no further (McDowall, 1978). The gill openings are in front of the round pectoral fins. The dorsal and ventral fins are of equal length and form a continuous fin running along the back, around the tail and onto the belly (refer to Table 1). Adult short-finned eels are golden-olive to olive-green on their back and sides. The belly is a silvery whitish-grey colour. As with other eel species, the female is larger than the male (Forest and Bird, 1992) growing up to 1200 mm in length weighing up to 3.5 kg (McDowall, 2000).
One of the closest species of A. australis is the long-finned eel (Anguilla dieffenbachii). Long-finned eels are larger and heavier than short-finned eels (Skrzynski, 1974) (refer to Table 1). The most distinguishing characteristic of the long-finned eel is that the dorsal fin extends much further along the back towards the head than the fin on the belly (McDowall, 1978; Skrynski, 1974). Other comparative features of long and short-finned eels are shown in Table 1.
|Anguilla dieffenbachii (long-finned eel)||Anguilla australis (short-finned eel)|
|Dorsal fin much longer than ventral fin||Dorsal fin approximately equal in length to ventral|
|Vomerine teeth in a narrow band||Vomerine teeth in a club-shaped formation|
|Eye above and forward of angle of jaw||Eye directly above angle of jaw|
|Lips thick||Lips thin|
|Head broad||Head narrow|
|Nasal organs prominent||Nasal organs small|
|Mouth gape wide and jaws strong||Mouth gape narrow and jaws small|
|Tail broad, caudal fin well developed||Tail narrow, caudal fin poorly developed|
|Pectoral fins prominent||Pectoral fins small|
|Dorsal area of body black; ventral side a yellowish-brown||Dorsal part greenish-brown; ventral a dull white|
|May reach over 180cm in length and 18kg in weight||Seldom grows over 90cm in length and 1.8kg in weight|
|Average length adult female, 85-95cm.||Average length adult female, 75-85cm.|
|Average length adult male, 55-65cm||Average length adult male, 35-45cm|
|Average weight adult female, 1.8-2.7kg.||Average weight adult female, 1.1-1.4kg.|
|Average weight adult male, 0.9-1.1kg||Average weight adult male, 0.25kg|
Full natural and naturalised range
The species A. australis is present in New Zealand, South eastern Australia, Tasmania, New Caledonia, Lord Howe, Norfolk, Fiji and possibly other islands in the south-western Pacific (McDowall, 1978). There are sixteen recognised species of Anguilla freshwater eels (McDowall, 1978); two of which occur in New Zealand (A. australis and A. dieffenbachii).
New Zealand range
Short-finned eels are widely distributed throughout New Zealand including the Chatham, Auckland and Campbell Islands (McDowall, 1978). The largest concentration is in the North Island.
Short-finned eels can be found throughout Canterbury; particularly in creeks, streams and lowland lakes such as Lake Ellesmere (Waihora), Lake Forsyth (Wairewa) and Wairarapa.
Natural History in Canterbury
The majority of the short-finned eel’s life is spent in freshwater (Close, 1992). They are found in lakes, streams, creeks and rivers but don’t tend to be found very far inland (Close, 1992; Jellyman, 1984). Short-finned eels prefer muddy waters and can be found amongst the debris in dark areas of river banks (McDowall, 2000). Some sightings and catches of short-finned eels around Canterbury include: Lake Ellesmere (Waihora), Lake Forsyth (Wairewa), Styx River, Waimakariri River, Hurunui River, Clutha River, Dudley Creek/ St Albans Creek sub-system and Mainstem at Dallington (Eldon & Kelly, 1992; Skrzynski, 1974).
In summer, once the short-finned eel has reached sexual maturity after spending 15 (for males) to 30 (for females) years in freshwater (McDowall, 2000), short-finned eels head close to the freshwater outlets near the coast. In this environment they go through a second stage of metamorphoses (the first being the leptcephalus stage in the first year of life) to prepare for migration out to the ocean in autumn. Morphological changes include the enlargement of the eyes (presumably for the deep, dark ocean depths), thinning of the lips and a colour change (McDowall, 1978). After swimming 5,000 kilometres in four months the short-finned eels, as suggested by Jellyman (2000), reach their spawning grounds somewhere between Fiji and Tahiti. Little is known on what actually happens once they get there. In the past the breeding process has been imagined as hundreds of spawning eels intertwining amongst each other to help squeeze out their eggs and sperm, each ejecting millions of eggs and sperm into the ocean where fertilisation occurs (Ayling, cited in Taylor, 1992). To heighten the chances of successful fertilisation, individual eels will try and join other spawning eel groups. After mating, their bodies are battered and worn-out and they then die (Ayling, cited in Taylor, 1992).
Short-finned eels eat a wide variety of foods. From water snails (Potamopyrgus), amphipods, earthworms (Annelida), bullies (Gobiomorphus spp. and Philypnodon spp.) to small fish including trout (Oncorhynchus spp.) and perch (Perca fluviatilis) (Jellyman, 1990). Short-finned eels are nocturnal, feeding at night (McDowall, 2000). With their stomachs being large and extendable, it is possible for them to eat large quantities at any one time; without having to eat each night (Jellyman, 1990). One study showed that the short-finned eel’s diet is inconsistent and depends on food availability, competition, season, water level and natural weather conditions (for example floods) (Jellyman, 1990). Jellyman also showed that a smaller eel’s diet largely consisted of small insects, whilst larger eels preferred to eat fish as large as the mouth allowed.
Research into the behaviour of A. australis is limited. However, McDowall (2000) describes them as being secretive and Jellyman (1990) describes them as being rather slow moving and energy conservative.
Although short-finned eels are known to have a diverse diet, little is known on how short-finned eels fit in to the food-webs of rivers and estuaries. However, one study showed short-finned eels were found in stomach contents of a number of native birds; being a particular favourite to the large black shag (Phalacrocorax carbo) (McDowall, 1978). Apart from birds, the largest predator of short-finned eels are humans.
How to find the Short-finned Eel
Short-finned eels can be found in high numbers at freshwater openings between February and March. At this time they swim downstream towards the sea for the long journey to their spawning grounds (McDowall, 1978). A more fascinating way to sight the short-finned eel in Canterbury would be at Kaitorete Spit (the gravel bar separating Lake Ellesmere (Waihora) and the Pacific). At night (at the same time of year) short-finned eels travel across the gravel, twisting and turning in their hundreds, making their way out to sea (Close, 1992).
Abundance and Conservation Status
- New Zealand: abundant
- Canterbury: abundant
They are abundant throughout New Zealand including Canterbury and the Chatham, Auckland and Campbell Islands (McDowall, 1978).
While short-finned eels are predominantly found in freshwater, they are rarely discovered out at sea (McDowall, 1978). Because they were abundant, easy to catch and nutritious, maori enjoyed eels as a staple part of their diet; particularly in Canterbury where kumara was hard to grow (Taylor, 1992 cited in Close, 1992). It wasn’t until after the development of full-scale eel fisheries in the 1960’s that the abundance of short-finned eels dropped, and they never recovered (Close, 1992). Close (1992) also found that before 1965 the annual eel catch was 15–20 tonnes. In 1975 that number had increased to an annual catch of 2364 tonnes.
The Department of Conservation (DOC) and the Ministry of Agriculture and Fisheries (MAF) manage the eel fishery in New Zealand. DOC manages the preservation of eels as an indigenous species, while MAF administers the commercial fishery. There is a reluctance to make any administrative decisions about the management of the fisheries as Maori claims under the Treaty of Waitangi could be breached (Close, 1992).
Significance for people
Traditional Maori significance and uses
There are over 150 different Maori names for eels in New Zealand, mainly because of their regional differences and the role in which eels hold in Maori life (Taylor, 1992 cited in Close, 1992). The assortment of names are also used to describe the various sizes, colour, habitat and taste of eels (Taylor, 1992 cited in Close, 1992). Tuna, for example, is the general name for freshwater eels, adding a verb after Tuna describes its difference (usually in appearance) (Strickland, 1990).
Eels are considered ‘taonga’ and have many mythological and phallic symbolisms associated with them (Taylor, 1992 cited in Close, 1992). One legend is that of Tuna (the personification of the eel). Tuna was believed to have come down from the sky because the heavens were too dry (Orbell, 1998). Another belief is that Tuna was killed because he tried to seduce Maui’s wife, Hine, while she was bathing. To kill him Maui dug a trench where Tuna was trapped, killed and cut into pieces. The pieces of Tuna turned into various life-forms: the head went to the rivers and became freshwater eels; his tail made it to the ocean to become the Conger eel (Conger verreauxi); and other parts of his body became numerous plants, vines. Finally his blood gives the rimu tree (Dacrydium cupressinum) its reddish colour (Orbell, 1998).
Digging out trenches along the lakes edge was, and still is one of the traditional methods Maori use to catch eels (personal experience). Other methods include; spear, net, pot or bait (Taylor, 1992 cited in Close, 1992).
Short-finned eels are eaten by people both here in New Zealand and overseas. They are regarded as a ‘taonga’ by maori and if a region is known for eels, they are still regularly offered to manuhiri (visitors) by the tangata whenua (people of the area) (personal experience). Eels are popular smoked. Additionally a favourite Cockney way of eating eels is jellied (personal experience).
Eel farming was established in the 1960’s and 70’s but with no success (Close, 1992). As a wild fishery, the New Zealand eel industry continues and does well. Exports overseas include: Belgium, Germany, the Netherlands and the United Kingdom (Close, 1992).
The short-finned eel is a native freshwater fish; it is smaller than the long-finned eel and is known for its abundance throughout New Zealand. A nocturnal creature, short-finned eels are most active at night and can be seen during their migration out to sea. The short-finned eel population is decreasing, mainly because of over fishing. With the joint efforts of DOC, MAF, iwi and the general public, controlling threats of habitat loss and over fishing will allow short-finned eels to thrive in New Zealand waters for future generations of short-finned eels and people alike.
Close, I. (1992). Eels are we pushing them to the edge?. Forest & Bird, 23(263): 10-15.
Eldon, G.A., & Kelly, G.R. (1992). Fisheries survey of the Avon River, 1991-1992. (New Zealand Freshwater Fisheris Report No. 137). Christchurch, New Zealand: Ministry of Agriculture and Fisheries.
Jellyman, D. (1990). Eels meals. Freshwater Catch, Summer(42): 15-16.
McDowall, R.M. (1978). New Zealand Freshwater Fishes: a Natural History and Guide. Auckland, New Zealand; Heinemann Reed.
McDowall, R.M. (2000). The Reed Field Guide to: New Zealand Freshwater Fishes. Auckland, New Zealand; Reed Books.
Orbell, M. (1998). A Concise Emcyclopedia of Maori Myth and Legend. Christchurch, New Zealand; Canterbury University Press.
Skrzynski, W. (1974) Review of Biological Knowledge on New Zealand Freshwater Eels (Anguilla spp.). (Fisheries Technical Report No. 109). Wellington, New Zealand: Ministry of Agriculture and Fisheries.
Strickland,R.R (1990). Nga tini a Tangaroa; a Maori-English, English-Maori dictionary of fish names. Wellington, New Zealand; MAF Fisheries.