fishes of the month
FISH OF THE MONTH - JANUARY
[Note: the scientific name of the
Indo-Pacific species is now Aetobatus ocellatus.
The Atlantic species remains A. narinari.
Aetobatus narinari (Euphrasen, 1790)
Kahe Point. O`ahu.
RAY · hailepo; hihimanu
Aetobatus narinari (Euphrasen, 1790)
magnificent rays can attain 6 ft. or more from wingtip to wingtip.
Their back, light brown, gray or black, is beautifully spotted with
white. The underside is mostly white often with a faint mazelike
pattern under the wings. The long slender tail can equal three times
the width of the body if not broken or bitten off, and bears 2-5
venomous spines at the base. Under the large protruding head is
a wide fleshy lobe somewhat resembling a "duck bill" which
is used to dig for molluscs and other organisms. When not foraging,
Spotted Eagle Rays swim well off the bottom, sometimes in small
groups. One of the most beautiful of all underwater sights is a
formation of Spotted Eagle Rays "flying" together in synchrony.
In some parts of the world schools of 50 or more have been reported,
but such behavior is certainly not common in Hawaiian waters. Occasionally
Spotted Eagle Rays will leap from the water, either dolphin style
or by cartwheeling with wings outspread. Leaping by pregnant females
is said to facilitate the birth of young.
Spotted Eagle Rays occur in warm seas
around the world and have long been considered a single species.
Recent research, however, reveals that the eastern Pacific and Indian
ocean populations host different species of tape worms in their
gut. Spot patterns and body proportions also differ between various
geographic populations. All this suggests that what we now call
Aetobatus narinari is actually a complex of several similar
species, but the details have yet to be sorted out.
The Hawaiian word hihimanu
means "lavish," "magnificent," "elegant."
In ancient times these powerful animals, which weigh up to 500 lbs.,
were forbidden to women as food. The species name, narinari,
is a Brazilian Indian word meaning "stingray." The family
Myliobatidae, to which this ray belongs, includes 22 species of
eagle rays, bat rays, duckbill rays, cownose rays, manta rays and
Hanauma Bay, O`ahu, 20 ft.
Eagle Rays pursuing one another may be about to mate.
Canham describes "a large eagle ray hotly pursued by two smaller
ones" at Molokini Islet, Maui. "The male latched onto the
larger female and coupled 10 feet in front of us, as the pair rapidly
glided out of sight."
Dr. Tim Tricas of the University of
Hawai`i observed two episodes of unsuccessful courtship at Enewetak
Atoll, Marshall Islands. In the first instance two males swam behind
a female on either side, nipping at her posterior margin. The female
rose to the surface and vigorously slapped her wings on the water
causing the males to back off. When she submerged the males continued
to follow and nip. Occasionally one would swim wide circles around
In the second episode, Tricas watched
as a single male followed a female, periodically gouging her back
with his dental plates and attempting to mount her. At each attempt
she either shied to one side or surfaced. When she swam at the surface,
the male followed either swimming conspicuously from side to side
or up and down. Eventually the female left and the frustrated male
swam in a wide circle alternately surfacing and diving at a 45 degree
angle, his white underside producing bright "flashes" visible
even after the outline of the ray disappeared in the distance.
In their book Sharks and Rays of
Hawai`i (Mutual Publishing, 2002), Gerald L. Crow and Jennifer
Crites write: "In Hawai`i, spotted eagle rays are born in October,
November and December in Pearl Harbor and Kane`ohe Bay, O`ahu, and
on the leeward side of Moloka`i. During the birthing process, these
rays have been seen leaping from the water and dropping their young
in midair." Up to four pups (disc width 10-20 inches) are born
Spotted Eagle Rays feed mostly on
molluscs. They will also take worms, crustaceans, echinoderms, and
small fish. The
mouth of an Eagle Ray contains platelike teeth used for crushing
shelled prey. Special papillae on the floor and roof of the mouth
separate the broken shell fragments from the edible flesh before
it is swallowed. Foraging rays
are thought use electroreceptors to "scan" for buried
prey, which they dig out using their shovel-like nose (the "duck
bill"). As they dig, sand may be stirred up in clouds or ingested
and expelled out the gill slits, enveloping the entire head. Fishes
will sometimes follow feeding Eagle Rays, presumably to snatch scraps.
Spotted Eagle Rays are not limited to foraging
in sand. Sometimes they will overturn large chunks of coral or rock
in search of prey, or rip prey animals directly from rocks. Pauline
Fiene, of Mike Severns Diving,
reports: "I was diving alongshore Maui
one morning and watched as an eagle ray worked at tearing something
off a large lava rock. With its head down and tail up in the 'air'
it worked away until it tore something off the rock with its lower
jaw and then swam off, chewing. When I went over to see what it
had gotten, I could see the byssal threads of the ark clam, Arca
ventricosa, still attached to the rock."
Nor are they afraid to tackle large
molluscs. Kendra Choquette-D`Avella, of Dive
Makai, reports: "Twice I have seen
eagle rays eating Triton's trumpet shells! I actually have an old
(crappy) photo of a ray with the pointy end of the shell sticking
out of its mouth! Both times the ray picked up the shell (and these
are BIG triton shells--not babies!) by the bulbous end and proceeded
to smash it against rocks to try to break it open. Both times I
was not able to see the end result but it is safe to assume the
Tritons got the worse end of the deal!"
for prey - Lana`i Lookout, O`ahu. 30 ft.
for prey - Kahe Point, O`ahu. 30 ft.
Eagle Rays as food
Sharks are the main predators of Spotted
Eagle Rays. Species known to feed on them in other parts of the world
include the Silvertip Shark(Carcharhinus albimarginatus) and
Great Hammerhead (Sphyrna mokarran). Although neither of these
is common in Hawaiian waters, the Tiger Shark (Galeocerdo cuvier)
is. Consider the following story by Matthew D'Avella of Dive Makai
Charters in Kailua-Kona, Hawai`i:
and I had heard word of a tiger shark that had taken a liking to Honokohau
Small Boat Harbor. One day after multiple sightings of the shark at
the mouth of the harbor, Kendra, our friend and co-worker Mark, and
I, decided to do a beach dive at "Manta Ray Bay" just outside
of the Harbor in hopes of catching a glimpse of this beautiful animal.
We entered the water at about 4:00 in
the afternoon. About 10 minutes into the dive we reached the pinnacle,
about 45 feet deep, and came upon an eagle ray. I later named him
Ray Ray. I got the idea that if I stayed close to the ray, and the
shark came to visit, then the ray might be a more tempting meal for
the shark than me. Besides, the ray was obliging my wishes and was
staying close to me too.
For the next 20 minutes I shot video
of Ray Ray swimming and digging in the sand for food or facing me
and looking at me. He was just staring at me, it was almost creepy
to be looking at his face. At times he was swimming so close to me
that I could not get his entire body in the view screen, or if I did
get the shot, I had my fin tips at the bottom of the video because
I was having to swim backwards to get away from him.
Towards the end of my encounter with
Ray Ray I met up with Mark and Kendra again. Kendra grabbed my hand
and had me feel her heart beat. To call her heart beat "racing"
would be an understatement. She is a very small girl and I could feel
her heart beating quite powerfully through her double 7mil wet suit.
We headed back into the beach and we
surfaced in 5 feet of water and Kendra told me of her encounter with
the tiger shark. Kendra said that the shark swam right over her head,
close enough to touch. She got two outstanding photos of the tiger
shark which later became known as Laverne. Kendra then proceeded to
tell me of what she saw of my encounter with the eagle ray. It seems
that while I was using the ray for cover from the shark, the ray was
using me for the same reason. Laverne and Ray Ray were playing 'ring
around the diver', and I didn't know it. All that I saw was the ray,
and all that I thought was "this video is going to be GREAT!"
Well the video of Ray Ray is outstanding.
I have some good shots of him feeding and swimming around me. After
watching the video a few times, I started to notice some jerking motions
from Ray Ray, was this in an effort to hide from Laverne? I suspect
yes. Should I ever get the chance to see an eagle ray up close and
face to face again, I am sure that I will feel an urge to turn and
look behind me. After all, I am a firm believer that my bravery in
the ocean realm is directly related to the amount of tape and remaining
battery power in my camera."
resting at the
Mahi wreck, leeward O`ahu. 80 ft.
does a Spotted Eagle Ray do all day?
Researchers in Bimini, Bahama Islands, tagged 17 individual rays
with small sonic transmitters and tracked them for periods of up
to 98 consecutive hours. They discovered two important facts: A)
The rays' activity fell into four phases which were strongly correlated
with the tidal cycle. B) The rays were strongly attached to three
"core areas" around the island, where they rested at low
"resting phase" began at low tide and lasted 2-4 hours
until the tide rose about half way to high. During this time the
rays tended to remain in their core areas, typically circling slowly
in small groups or swimming gently into the current .
As the tide continued to rise and approached its high point, the
rays increased their swimming speed and began moving out of their
core areas. Researchers called this the"commuting phase."
Feed and socialize
At high tide the rays entered the "foraging phase," moving
in slow circles, feeding, and socializing. This lasted for several
hours until the tide fell about half way to low.
As the tide continued to fall and approached low, the rays entered
the "returning phase," and began swimming back to their
core areas. Movements were slow and the rays were loosely grouped.
1) Spotted Eagle Rays have one of the largest brain to body weight
ratios of any fish.
2) Spotted Eagle Rays are the only members of their family to have
multiple spines on the tail.
2) The earliest reference to the native Brazilian name "narinari"
from which the scientific species name was drawn appears in a book
on the natural history of Brazil written by a French monk and published