New Zealand longfin eel
Encyclopedia
The New Zealand Longfin eel (Anguilla dieffenbachii) is one of three freshwater eels found in New Zealand. The other two species of eel are the Shortfin eel
(Anguilla australis) which is also found in south-eastern Australia and the recently arrived Australian Longfin eel
(Anguilla reinhardtii).
The easiest method for identification of the New Zealand Longfin eel is by the length of its fins: the dorsal
(top) fin extends further forward towards the head than the anal
(bottom) fin. In the Shortfin Eel the fins are of similar lengths.
family Longfin Eels have a rather unusual migration system where they grow and mature into fertile adults in freshwater water systems then migrate to the sea to breed; a catadromous breeding system.
This breeding system also ensures that their mating system is randomised (panmictic population).
The New Zealand Longfin eel is a very long lived fish with records of females reaching 106 years old and weighing up to 24 kg. Longfin Eels have the slowest growth rate of any eel species studied.
Male and female Longfin Eels differ in length and in the age at which they migrate with males averaging 666 mm but reaching up to 735 mm in length with an average age of 23 years (12 – 35 years). Female Longfin Eels are considerably larger with an average length of 1156 mm, but can range from 737 to 1560 mm. These females range in age from 20 to 60 years before migrating.
The average age of migration varies between the North
and South Island
s of New Zealand with the North Island
eels having younger migration ages and thus faster generation times.
Longfin eels life cycle like other species of Angullidae eels is rather complex consisting of four distinct life stages which remained a mystery for many decades and still is not fully understood.
When migrating Longfin eels reach their breeding and spawning grounds (which is thought to be located in the tropics of the pacific ocean somewhere near the Fijian basin) their eggs (of which each female eel produces between 1 and 20 million) are fertilized in an unknown manner but is thought to occur in deep tropical water. The eggs then float to the surface hatching into very flat leaf-like larvae (leptocephalus
larvae) they then drift along large oceanic currents back to New Zealand. This drifting is thought to take up to 15 months. There have been no recorded captures of either the eggs or larvae of Longfin eels.
Upon arrival back in New Zealand the larvae undergo a transformation (metamorphosis
) into glass eels which resemble small adult eels but are transparent. These glass eels occupy estuaries during which time they develop colouration and become elvers, resembling small adult Longfin eels. The elvers migrate upstream where they develop into adults.
of glass eels into the freshwater river networks in New Zealand is a very variable process which is thought to be affected by the El Niño and La Niña
Southern Oscillations. This is a major reason for the failure of Longfin eels aquaculture
farms in the 1970’s.
larvae
. When eels become larger, they also feed on small fish including galaxiids and trout
.
waterways including the Chatham Islands
.
Longfin eels are often found great distances inland (up to 361 km) along fresh waterways and in high country lakes which are connected to the sea. Aiding in Longfin eels inland distribution is its climbing ability when it is in its elver (juvenile) life stage and is under 12 cm in length. These migration
events frequently coincide with increased temperate, water flow and low light conditions. At this size the elvers can migrate
up to 130 km inland over a summer and has been observed climbing near vertical surfaces up to 43 m tall. This feat is accomplished through a combination of surface tension
(with the water) and friction
.
The in-stream distribution varies depending on the life stage of the Longfin eel. As elvers (juveniles) they prefer shallow water (under 0.5 m deep) with coarse substratum
and faster than average stream flow (such as that found in stream riffle
).
Adult Longfin eels tend to be found next to or under large pieces of debris
and undercut river banks.
) source. Reflecting this significance for Māori they had extensive knowledge of Longfin eel’s migratory
routes.
of Longfin eels started to gain momentum in the 1960’s and had a 2000 tonne yearly catch by the 1970’s. But the fishery went into decline in the early 1980’s and in the 2000-2001 fishing season only 1079 tonnes were taken.
The commercial Longfin eel fishing was included into the Quota Management System
(QMS) in 2000 for the South Island
and the North Island
in 2004. This set limits as to the minimum and maximum size (220 grams and 4 kg) and the Total Allowable Catch (TAC). As of 2007 the TAC has not been reached in any fishing season since the implementation of the QMS
.
In recognition of the significance of Longfin eels to Māori they have a 20 percent allocation of fishery stocks.
The capture and export of glass eels in New Zealand has been prohibited.
operation. The first were in the 1970’s. These did not remain operational for long with the last farm closing in 1982. The most common reasons for these failures were economic (the high cost of production vs low price for the eels), variable recruitment of glass eels and the high mortality (death) rates in the farms.
In the early 2000’s there has been renewed interest in the aquaculture of Longfin eels due to the increasing knowledge of Longfins biology and the diminishing stocks of European eel
s (Anguilla Anguilla) but no farms have been built.
Short-finned eel
The short-finned eel, Anguilla australis, is one of the 15 species of eel in the family Anguillidae. It is native to the lakes, dams and coastal rivers of south-eastern Australia, New Zealand, and much of the South Pacific, including New Caledonia, Norfolk Island, Lord Howe Island, Tahiti, and...
(Anguilla australis) which is also found in south-eastern Australia and the recently arrived Australian Longfin eel
Speckled longfin eel
The speckled longfin eel, Australian long-finned eel or marbled eel, Anguilla reinhardtii, is one of 15 species of eel in the family Anguillidae. It has a long snake-like cylindrical body with its dorsal, tail and anal fins joined to form one long fin. It usually has a brownish green or olive green...
(Anguilla reinhardtii).
The easiest method for identification of the New Zealand Longfin eel is by the length of its fins: the dorsal
Fish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...
(top) fin extends further forward towards the head than the anal
Fish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...
(bottom) fin. In the Shortfin Eel the fins are of similar lengths.
General Biology
Like other members of the AnguillidaeAnguillidae
Anguillidae is a family of fishes that contains the freshwater eels. There are 19 species/subspecies in this family, all in genus Anguilla. They are catadromous, meaning they spend their lives in freshwater rivers, lakes, or estuaries and return to the ocean to spawn...
family Longfin Eels have a rather unusual migration system where they grow and mature into fertile adults in freshwater water systems then migrate to the sea to breed; a catadromous breeding system.
This breeding system also ensures that their mating system is randomised (panmictic population).
The New Zealand Longfin eel is a very long lived fish with records of females reaching 106 years old and weighing up to 24 kg. Longfin Eels have the slowest growth rate of any eel species studied.
Male and female Longfin Eels differ in length and in the age at which they migrate with males averaging 666 mm but reaching up to 735 mm in length with an average age of 23 years (12 – 35 years). Female Longfin Eels are considerably larger with an average length of 1156 mm, but can range from 737 to 1560 mm. These females range in age from 20 to 60 years before migrating.
The average age of migration varies between the North
North Island
The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...
and South Island
South Island
The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...
s of New Zealand with the North Island
North Island
The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...
eels having younger migration ages and thus faster generation times.
Life stages
When migrating Longfin eels reach their breeding and spawning grounds (which is thought to be located in the tropics of the pacific ocean somewhere near the Fijian basin) their eggs (of which each female eel produces between 1 and 20 million) are fertilized in an unknown manner but is thought to occur in deep tropical water. The eggs then float to the surface hatching into very flat leaf-like larvae (leptocephalus
Leptocephalus
A leptocephalus is the flat and transparent larva of the eel, marine eels, and other members of the Superorder Elopomorpha. Fishes with a leptocephalus larva stage include the most familiar eels such as the conger, moray eel, and garden eel, and the freshwater eels of the family Anguillidae, plus...
larvae) they then drift along large oceanic currents back to New Zealand. This drifting is thought to take up to 15 months. There have been no recorded captures of either the eggs or larvae of Longfin eels.
Upon arrival back in New Zealand the larvae undergo a transformation (metamorphosis
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
) into glass eels which resemble small adult eels but are transparent. These glass eels occupy estuaries during which time they develop colouration and become elvers, resembling small adult Longfin eels. The elvers migrate upstream where they develop into adults.
Recruitment
The recruitmentRecruitment (biology)
In biology, recruitment occurs when juvenile organisms survive to be added to a population. The term is generally used to refer to a stage whereby the organisms are settled and able to be detected by an observer....
of glass eels into the freshwater river networks in New Zealand is a very variable process which is thought to be affected by the El Niño and La Niña
La Niña
La Niña is a coupled ocean-atmosphere phenomenon that is the counterpart of El Niño as part of the broader El Niño-Southern Oscillation climate pattern. During a period of La Niña, the sea surface temperature across the equatorial Eastern Central Pacific Ocean will be lower than normal by 3–5 °C...
Southern Oscillations. This is a major reason for the failure of Longfin eels aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
farms in the 1970’s.
Sex determination
The determination of the sex of Longfin eels is a difficult process as their sexual organs are not determined until they are over 450 mm in length. The only method to determine Longfin eels sex is through internal examination and only becomes easy to distinguish when the eels mature and migrate.Diet
Longfin eels have an omnivorous diet and are opportunistic feeders. Their diet as small eels largely consists of insectInsect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
. When eels become larger, they also feed on small fish including galaxiids and trout
Trout
Trout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...
.
Habitat and Distribution
The New Zealand Longfin eel is an endemic species to New Zealand with a very wide distribution through New Zealand’s freshwaterFreshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
waterways including the Chatham Islands
Chatham Islands
The Chatham Islands are an archipelago and New Zealand territory in the Pacific Ocean consisting of about ten islands within a radius, the largest of which are Chatham Island and Pitt Island. Their name in the indigenous language, Moriori, means Misty Sun...
.
Longfin eels are often found great distances inland (up to 361 km) along fresh waterways and in high country lakes which are connected to the sea. Aiding in Longfin eels inland distribution is its climbing ability when it is in its elver (juvenile) life stage and is under 12 cm in length. These migration
Animal migration
Animal migration is the relatively long-distance movement of individuals, usually on a seasonal basis. It is a ubiquitous phenomenon, found in all major animal groups, including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. The trigger for the migration may be local...
events frequently coincide with increased temperate, water flow and low light conditions. At this size the elvers can migrate
Animal migration
Animal migration is the relatively long-distance movement of individuals, usually on a seasonal basis. It is a ubiquitous phenomenon, found in all major animal groups, including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. The trigger for the migration may be local...
up to 130 km inland over a summer and has been observed climbing near vertical surfaces up to 43 m tall. This feat is accomplished through a combination of surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
(with the water) and friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
.
The in-stream distribution varies depending on the life stage of the Longfin eel. As elvers (juveniles) they prefer shallow water (under 0.5 m deep) with coarse substratum
Substratum
In linguistics, a stratum or strate is a language that influences, or is influenced by another through contact. A substratum is a language which has lower power or prestige than another, while a superstratum is the language that has higher power or prestige. Both substratum and superstratum...
and faster than average stream flow (such as that found in stream riffle
Riffle
A Riffle is a short, relatively shallow and coarse-bedded length of stream over which the stream flows at higher velocity and higher turbulence than it normally does in comparison to a pool....
).
Adult Longfin eels tend to be found next to or under large pieces of debris
Debris
Debris is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, in geology, large rock fragments left by a melting glacier etc. The singular form of debris is debris...
and undercut river banks.
Significance for Māori
The Longfin eel is an important resource for Māori because it provided an important food (proteinProtein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
) source. Reflecting this significance for Māori they had extensive knowledge of Longfin eel’s migratory
Animal migration
Animal migration is the relatively long-distance movement of individuals, usually on a seasonal basis. It is a ubiquitous phenomenon, found in all major animal groups, including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. The trigger for the migration may be local...
routes.
Longfin eel fishing
The commercial fishingCommercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
of Longfin eels started to gain momentum in the 1960’s and had a 2000 tonne yearly catch by the 1970’s. But the fishery went into decline in the early 1980’s and in the 2000-2001 fishing season only 1079 tonnes were taken.
The commercial Longfin eel fishing was included into the Quota Management System
Quota Management System
The Quota Management System is a type of individual fishing quota that is used in New Zealand to manage fish stocks.It is the first ever property-based fisheries management system to be implemented.-External links:* – The Quota Management System...
(QMS) in 2000 for the South Island
South Island
The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...
and the North Island
North Island
The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...
in 2004. This set limits as to the minimum and maximum size (220 grams and 4 kg) and the Total Allowable Catch (TAC). As of 2007 the TAC has not been reached in any fishing season since the implementation of the QMS
Quota Management System
The Quota Management System is a type of individual fishing quota that is used in New Zealand to manage fish stocks.It is the first ever property-based fisheries management system to be implemented.-External links:* – The Quota Management System...
.
In recognition of the significance of Longfin eels to Māori they have a 20 percent allocation of fishery stocks.
The capture and export of glass eels in New Zealand has been prohibited.
Longfin eel aquaculture
There have been a number of attempts at growing Longfin eels in an aquacultureAquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
operation. The first were in the 1970’s. These did not remain operational for long with the last farm closing in 1982. The most common reasons for these failures were economic (the high cost of production vs low price for the eels), variable recruitment of glass eels and the high mortality (death) rates in the farms.
In the early 2000’s there has been renewed interest in the aquaculture of Longfin eels due to the increasing knowledge of Longfins biology and the diminishing stocks of European eel
European eel
The European eel, Anguilla anguilla, is a species of eel, a snake-like, catadromous fish. They can reach in exceptional cases a length of 1½ m, but are normally much smaller, about 60–80 cm, and rarely more than 1 m....
s (Anguilla Anguilla) but no farms have been built.