Poor Knights marine reserve fish, fish and more fish: the legendary fish schools
of the Poor Knights by Dr J Floor Anthoni (2007)
www.seafriends.org.nz/issues/res/pk/fish_schools.htm
New Zealand is famous for its schools of surface-feeding
fish, the demoiselles, blue maomao, trevally and pink maomao. If watching
them from the surface is spectacular, being near them in the water becomes
a challenge to describe.
blue maomao: the most spectacular schooling
fish of the Poor Knights
f052629: A mixed school of trevally and blue maomao at
25m depth, Fred's Pinnacle.
blue maomao Blue Maomao (Scorpis violaceus) are the ambassadors for the
Poor Knights. They are a New Zealand species, occurring in the warmer waters
around the North Island, and at the Kermadec Islands. When old (up to 40cm
and 10-20 years) they are iridescent blue, a coloration that develops with
age, from the pale blue young. Juvenile blue maomao even have a yellow
anal fin.
Although blue maomao are found swimming in open water, they are not truly
pelagic because they return to their sleeping spots on the rock at night.
Visitors to the Poor Knights delight in seeing schools of blue maomao,
numbering hundreds to thousands, feeding on the surface. Schools of young
fish then colour the water light blue, whereas old fish cause a deep blue
iridescence. Blue maoamo have their eyes set right in the front of their
heads, right above their small but flexible mouths. When they collectively
ruffle the water's surface while feeding in a frenzy, they actually see
their prey (fast moving shrimps), as their mouths snap left, front and
right, without their bodies needing to move likewise. With their large
breast fins and disc-like shape, these fish are very agile, a necessity
for zooplankton feeding.
.
f990135: divers on charter boat Pacific Hideaway observing
a surface-feeding school of blue maomao.
f013003: the moment of woosh when the school decides to dive,
as if attacked from above by sea birds.
f024623: the old blue maomao are no longer found on the poor
knights. This young school stopped feeding to inspect the photographer.
f011922: a school of young blue maomao.
f049031: even during daytime, after a good breakfast, blue
maomao often take a rest. Here they come down from the rock in the distance,
in order to investigate the photographer.
f031312: blue maomao and demoiselles at the Kermadec Islands.
f024134: blue maomao in Northern Arch.
f045426: blue maomao in Middle Arch. See if you can spot
the sweep amongst them. When young, they look very similar.
f023115: blue maomao in Blue Maomao Arch.
trevally Silver trevally (Pseudocaranx dentex) belong to the family of
jacks, fast swimming pelagic fishes. They are all characterised by a narrow
tail stock and a deeply forked tail. Others belonging to this family are:
kingfish (Seriola lalandi), koheru (Decapterus koheru) and
jackmackerel (Trachurus novaezelandiae, T declivis). When young,
trevally are found in small groups fossicking over sandy bottoms but later
they will swim in the open, hunting fast swimming planktonic shrimps. They
often team up with kahawai (Arripis trutta).
Trevally can grow old, up to 30 years, even though they are an important
source of food in the food chain. Old trevally have blunt snouts, now rare.
f219005: we often forget what a surface feeding school used
to look like. Notice the boat in the distance? This combined school of
trevally and kahawai with all the shearwaters above it, is a quarter of
a hectare in size (half football field), counting many thousands of fish.
f990136: a school of trevally feeding at the surface.
f041118: close-up of a school of trevally (Pseudocaranx dentex),
passing close by.
f052625: young silver trevally circling around the photographer.
f052629: a mingle of trevally and blue maomao at Fred's Pinnacle.
f001017: a 3-4 year old trevally (Pseudocaranx dentex)
showing vertical bands and a yellow side stripe and tail stock. It can
turn these patterns and colours on or off at will.
f020829: old trevallies of over 10 years old, with their
blunt snouts, have become very rare but here is a group of about 8 years
old.
f001823: occasionally schools of kahawai or sea trout (Arripis
trutta) visit the Poor Knights, often mixed with trevally.
demoiselles The two-spot demoiselle (Chromis dispilus) is such a darling
little fish. Also called sea swallow because of its forked tail, the name
chromis means blue, as in the family of damselfishes, the colour blue is
dominant. Here on the Poor Knights one can encounter the much rarer single
spot demoiselle (Chromis hypsilepis) and the rarer still, yellow
demoiselle (Chromis fumea). The females are always greenish-black,
whereas the males become more blue as they grow older, as also their tails
grow whiter. Most demoiselles seen these days are no older than 3-4 years.
Demoiselles feed on small zooplankton organisms, reason why their eyes
are set so close above their mouths. They swim only with their strong breast
fins, which moves their bodies rapidly up and down and sidewards. In addition
their lips can extend far out and sideways to catch the bug that almost
got away. Although demoiselles feed on zooplankton, they are never far
away from the rock face. When food is plentiful, one can see them resting
underneath and in amongst seaweeds. They also take a rest when the tide
changes, and currents stop running.
The change in tide also spurs them to migrate, often for kilometres,
along the rock face to another spot that will give more advantage in the
turning tide. Divers may see endless streams of demoiselles migrating,
often at around 20-25m depth, along invisible paths, and in densities that
never fail to amaze.
When demoiselles leave the depth after a rest, to feed again in shallow
water, they have to ascend slowly because the pressure of the water diminishes,
which expands their swim bladders. An ascent from 30m to the surface causes
their swim bladders to expand four-fold, so they need to 'compensate' by
degassing. Because this is a slow process, they often group together in
high densities, while ascending slowly.
At night all demoiselles descend onto the rock to their private little
hollow in the rock face where they are the most common fish seen during
a night dive.
f041125: demoiselles huddling under a stalked kelp after
a good breakfast. Note the young blue maomao in the foreground, still with
a yellow anal fin.
f043108: demoiselles amongst the tangle wrack (flexible weed).
Here they are safe from marauding attacks of shags and gannets.
f051116: wherever a diver goes, there are demoiselles showing
real interest.
f051120: a diver surrounded by young demoiselles that show
no fear at all.
f038218: a male demoiselle in the serious business of fanning
its brood of a few hundred eggs.
f038228: a super macro close-up of demoiselle eggs on top
of a bryozoan mat, shows two eyes peering out of each egg.
f049004: demoiselles in their thousands, forming a tight
formation. This is not a feeding aggregation but a consensus call for surface-feeding.
f049000: demoiselles streaming away from the photographer
on their slow ascent to shallow plankton-rich waters.
f052735: the one-spot demoiselle (Chromis hypsilepis)
is much rarer than the two-spot demoiselle, and the yellow demoiselle (Chromis
fumea) rarer still.
pink maomao Pink maomao (Caprodon longimanus) are spectacular for their
soft pink colours, elegant shapes and almost royal behaviour. Never in
a hurry, they move at greater depths between 20 and 50m where zooplankton
is less prolific. Not surprisingly, these fish live in the slow lane, expending
but little energy, while growing very old (40 years?). The pink maomao
is not closely related to the blue maomao, but to perches. In their midst,
one may encounter one of the most beautiful fishes in New Zealand, the
splendid perch (Callanthias australis), also a deep water fish.
Very little is known about the pink maomao. Our own observations show that
it has largely survived a sequence of three mass mortalities (1983, 1992,
2001).
f021132: pink and blue, a school of pink maomao, first attracted
y the photographer, now moving past.
f041806: pink maomao (Caprodon longimanus) are often
found resting in cool deep water of 30m or more.
f023625: a school of pink maomao showing interest in the
diver at Landing Bay Pinnacle.
f048407: a resting pink maomao (Caprodon longimanus)
changes colour, showing light blotches. At night they can become orange-red.
f036503: female northern splendid perch (Callianthias
australis) is found at the boundary of diving depths, in 40-50m and
always near a cave. The male is very beautiful.
f048408: a female butterfly perch (Caesioperca lepidoptera)
at sleep, has turned from salmon-pink to brown-grey.
The butterfly perch (Caesioperca lepidoptera) forms small schools,
never further than a few metres away from the rock face, at depths between
15 and 35 metres. Their normal colour is salmon-pink, while males have
an iridescent spot above their eyes. At night they become dark brown.
koheru Koheru (Decapterus koheru) is the bait fish of the Poor Knights.
This is a truly pelagic fish, and seeing it at the Poor Knights could just
be because it was passing by. However, divers have known persistent schools
of koheru belonging to certain places at the Poor Knights. When young,
they can easily be confused with the more coastal, but also pelagic jackmackerel,
distinguished by the Z in its side line.
However, as koheru grow older, it also becomes more yellow on top and bluish
on its sides. It is a very beautiful fish, particularly the old ones by
night.
f021834: 2-year old koheru (Decapterus koheru) in
a feeding frenzy at the surface. For a photographer a fast moving nightmare.
f048330: one-year old koheru seeking refuge near tall flexible
weeds.
f045632: two year old koheru and diver.
f024704: a school of koheru staying around the diver for
protection.
f041827: 3-year old koheru have bright yellow backs and very
reflective bluish bellies. They can turn their yellow colour off at will.
f045634: 3 year old koheru, still young.
golden snapper The golden snapper (Centroberyx affinis) is not a schooling
fish at diving depths, but deeper down at 50-100m, it forms large groups
that migrate nearer to the surface at night. Divers encounter golden snapper
in small groups, hiding inside caves by day, while feeding from plankton
organisms at night. Their large eyes are very light-sensitive, which enables
them to hunt by weak moonlight and even in total darkness, because many
nocturnal zooplankton organisms produce light.
Like the related slender roughy (Optivus elongatus) and the common
roughy (Paratrachichthys trailli), the golden snapper hangs motionless
in the water, moving in a start-stop manner in order to be able to estimate
the movement of its prey. Its neural networks have been wired to intercept
prey rather than pursuing it - amazing.
f048728: a mature golden snapper (Centroberyx affinis)
in motionless suspension.
f038425: golden snapper patiently waiting for the night,
hiding under an overhang by a small cave.
.
