SHORTFIN
EEL (Anguilla australis)
Synonymy: tuna,
silverbelly eel
| Shortfin
and longfin eels are elongate fish belonging to the Family
Anguillidae, having joined dorsal, caudal and anal fins
forming a single fin right around the tail with no visible
fin rays. They also have a single slit gill opening on either
side of their head and no pelvic fins. |
 |
The longfin eel is found exclusively within New Zealand whereas
the shortfin eel is more widespread, being found around southeastern
Australia and other southern Pacific islands. Although both
species can occur together, longfin eels are more common in
inland waters, whereas shortfin eels are more common near the
coast.
Both species are among the most commonly encountered and best-known
of New Zealand’s freshwater fishes, the general awareness
perhaps due to the largely unjustified fear that they have inspired.
DIET
Eels have very strong jaws (to which the occasional angler who
has been bitten will testify), but despite this, their teeth
are very small and numerous and they cannot bite through tough
food. They have to either swallow food whole or grip onto the
food and then tear pieces free by either twisting or whipping
their bodies.
When they are smaller, eels will feed predominantly on small
aquatic invertebrates and fish but as they grow older and larger
they will target other prey such as larger fish, including other
eels, and even mice and ducklings!
Did
you know?
An eel’s vomerine teeth have a set pattern, which is dependent
on the species. This pattern can be established by pressing
plasticine into the roof of an eel’s mouth!
LIFE HISTORY
Eels grow slowly, with longfin male eels maturing at an average
age of 23 years (48-74 cm) and females at 34 years (75-180cm).
Shortfin males mature at an average of 14 years (38-55cm) and
females at 22 years (50-100cm). Larger size in females occurs
as this enables them to produce a greater number of eggs. The
breeding instinct is so strong that eels will leave the water
to navigate their way around obstacles such as dams and weirs,
on their way to the sea. The sequence in which eels migrate
out to sea is thought to be with shortfin males leaving first
in February-March, and shortfin females soon after, followed
by longfin males in April and then longfin females in late April
and May. These migratory eels go through several changes prior
to migration- their heads become more streamlined, their eyes
enlarge (with a blue ring appearing around them) and their gut
degenerates, resulting in loss of appetite. After completing
the long migration out of the freshwater and up into the sub-tropical
Pacific breeding grounds, both species breed and then die.
The resulting ‘willow leaf-like’ leptocephalus larvae
are brought back to New Zealand over a period of around eighteen
months on oceanic currents. They change form to that of a ‘glass
eel’ when they are close to our coast and then move into
the freshwater, taking on pigmentation within two weeks. These
miniature eels are known as elvers and will move inland to find
suitable habitat, where they will grow until mature, completing
the cycle.
LEGENDARY
EELS
South Island Maori legend states the origin of Tuna, the eel,
is from the heavens known as Orukateraki. Due to the heat of
the sun and the lack of water, Tuna's skin had been burnt and
turned black which made him sad. After meeting Tawhaki, a man
who had travelled from the earth to the heavens, Tuna descended
to Papatuanuku, the earth, where he found a cool pool in which
to live called Muriwaiowhata. Sometime later, Tuna was discovered
by a woman named Hineturepo, who saw Tuna as a taniwha, or monster.
The people of the area caught Tuna in a large hinaki (eel pot),
killed him and cut him into pieces. The pieces of Tuna were
scattered and became the various types of ‘eel’
we have today; the conger eel, the lamprey, the hagfish and
the freshwater shortfin and longfin fin eels.
Worldwide there are stories and legends about eels; one in particular
gives the eel its scientific Family name Anguillidae. This came
from Greek mythology where the white armed goddess Anguilla
and the king of Greek gods Jupiter together produced eels.
DID
YOU KNOW?
To Maori the shortfin and the longfin eel are known as Tuna.
Migratory eels are known as Tuna-heke as they cannot be caught
using bait (they have no appetite because their digestive system
has started to degenerate).
