Long Fin Eel

Longfin eels are only found in New Zealand and occur throughout the country.

Māori name = tuna kuwharuwharu. Scientific name = Anguilla dieffenbachii

The longfin eel has lived in New Zealand for 80 million years. It is our top freshwater predator and therefore important to the biodiversity of our waterways. Since the mid-1800s the longfin eel has been so undervalued that if we do not start to appreciate this fascinating fish it may soon be extinct.

Longfin eels are found

In all the creeks and streams in and around the Tangihua ranges

Longfin eel description

There are three eel species, all from the Anguillidae family of fish:

• longfin eel Anguilla dieffenbachii, found further inland
• shortfin eel A. australis, found on the coast
• spotted eel A. reinhardtii, which may have recently arrived from Australia and is found only in northern rivers.

Longfin eel distinguishing features

Longfin eels are distinguished from shortfin eels

• By the length of the dorsal fin; when viewed side-on, the dorsal fin is longer than the anal fin and extends well forward past the end of the anal fin. In shortfin eels, the dorsal and anal fin ends are almost the same length.
• A longfin’s mouth extends past its eyes, further than a shortfin’s.
• When a longfin eel bends its loose skin wrinkles distinctively inside each bend, where a shortfin eel’s skin is smooth
• the only endemic freshwater eel species in New Zealand.
• Migrating longfin migrate males in April. Shortfin males migrate in February–March. The females soon follow
• The longfin eel is the largest of the eels and so is at the top of the fresh water fish food chain when they are adults.
• Longfin males an average of 23 years 48–74 centimetres, females at 34 years 75–180 centimetres.
• Shortfin males at an average of 14 years 38–58 centimetres, females at 22 years 50–100 centimetres.

Long finned eels are probably the world’s biggest eels. They may grow up to 1.75 metres. The biggest caught and measured, so far, weighed 24 kilograms. Any New Zealand eel over 1 metre long and caught inland is probably a longfin specimen

Life cycle

picture Te Ara – The Encyclopedia of New Zealand

The longfin eel life cycle has distinct stages.

• Adult in our rivers
• Eggs in the open ocean
• Larva in the ocean
• Glass eel
• elver

The long fined eel adult lives in fresh water. The males live between up to 35 and do not mature until they are 23 to 25 years old. Females don’t mature until they are 34 years old and they could be 80 years old before they migrate. The females being older also tend to be the bigger eels.

They breed only once and then die

Adult long fin eels migrate to sea to breed. They leave in the autumn travelling to their spawning grounds in Tonga, a trip of 6,000 of km. The female produce between 1 million and 20 million eggs and these are fertilised by the males. The eels then die.

The eggs float to the surface of the ocean and hatch out as leaf-shaped larvae called leptocephalus. These larvae float back to New Zealand on the oceans currents. This can take between 15 and 17 months. They arrive in July through to December, similar to white bait.

Once the eels reach New Zealand they transform into glass eels. These look like transparent juvenile eels.

The glass eels then live in the estuaries for about a year. During this time they turn darker and become elvers. As elvers, they migrate up stream, they climb water falls and small dams to where they will mature and live as adults. Juvenile eels prefer shallow water under 0.5 m deep e.g stony streams with faster than average stream flow. Adult longfin eels tend to be found next to or under large pieces of debris and undercut river banks

Adult eels will travel across land on wet nights to inhabit ponds and swamps which have no streams flowing from them or into other streams.

Metamorphosis

Female longfin eels go through amazing changes to help them on their long journey. They need plenty of energy and an ability to hide from large sea based predators during the four month trek. Longfin females normally have a big bulgy head but when they are preparing to migrate this becomes more tapered and looks like a bullet. Their eyes grow to twice normal size to help with swimming through deep dark sea water. They store fat and then stop eating.

The sexual organs grow pushing internal organs into a small space of the stomach cavity

Longfin eel interesting facts – from Joseph Potangaroa

• Has lived in New Zealand for 80 million years.
• Is the biggest freshwater eel in the world.
• Is our top freshwater predator.
• Is endemic, which means it is found no where else in the world
• Is diadromous, which means they migrate between freshwater and the sea. In particular eels/tuna are catadromous which means they spend their adult life in fresh water before swimming to the sea to breed and die. Salmon are anadromous which is the opposite to catadromous while kōaro stay in freshwater to spawn get washed out to sea for six months and then return to freshwater, this is referred to as amhidromy.
• Eels have a bone in their ears called an otolith. These bones have annual rings on them like a tree.
• The oldest eel found so far was 106 years old.
• Officially the heaviest eel weighed 24 kilograms. Some have been reported up to 50 kilos
• Females can grow to 2 metres in length. and males are never more than 1metre long
• If moist can spend up to 48 hours out of water.
• Have slime that helps them to breath and protects skin when out of water. Can absorb up to 50% of oxygen needs directly through the skin. They also get slimy when they are stressed.
• Have bad eyesight but amazing sense of smell. The nostrils are the tubes that stick out from the end of their nose.
• Have sensors that detect movement in front of them. The sensors look like white spots around the lips.
• Have scales embedded in their skin instead of on the outside.
• Like to spend daytime under banks, rocks and logs.
• Come out at night to feed on insect larvae, snails, fish, kōura, dead animals and birds
• Have rows of small sharp teeth that point backwards into the mouth.
• Are not as active during winter as they prefer warmer water temperatures.
• Large females may require 400 metres of home territory

Habitat

• They live mainly in rivers and inland lakes but can be found in almost all types of waters, usually inland from the coast.
• They prefer waterways with shade from overhanging trees or banks and clean water. But they can survive in farm drains, large ponds, farm dams and areas with quite murky water

Eels diet

Eels are omnivorous. They prey on fresh water fish, insects and insect larvea depending on their age. The are cannibals and scavengers, feeding on smaller eels and dead animals which have fallen into the water.

Maori

Eels played an important role as a source of food for Maori, especially those living away from the coast.

Māori studied eels intensively to determine life cycles, ages, habitat and migration patterns. This knowledge helped them determine how many eels they could take for food before depleting numbers to a dangerous level. Eeling would occur at special times of the month and year according to a range of environmental indicators e.g. lunar cycles

They were caught using variety of methods, weirs built on rivers, with traps, nets, spears and bait.

The traps hinaki is the most common method still used. It is a net formed into a bag with a long entrance way and holding bag. Some have two entrances. The bait was put in the top of the holding bag and eels would swim through the entrance up into the holding bag. Sharp sticks pointing into the holding bag would allow the eel to pass through but not allow then out again.

Once caught, eels were preserved by drying on lines, or smoking over fires.

Farming and reseeding were not uncommon. This meant restocking waterways or holding eels in specially built enclosures. Blind trenches were dug close to migration passages during the migrating season. This tricked the eel into thinking it was entering a normal stream. Once the trenches were filled with eel they were blocked off and the eels harvested.

Referances

Joseph Potangaroa – Tuna Kuwharuwharu

Niwa
Te Ara
Wikipedia