Showing posts with label fish. Show all posts
Showing posts with label fish. Show all posts
Tuesday, August 5, 2008
Tuesday, July 29, 2008
Tuesday, July 8, 2008
Tuesday, July 1, 2008
BNSullivan.jpg "Blue Spotted Stingray (Taeniura lymma) at Pulau Sipadan")
Tuesday, June 10, 2008
Monday, June 9, 2008
On a collision course with critters in the sea
This post was inspired by a comment on our Rush Hour On the Reef photo in which Chris asked, "It's probably a fairly silly question, but do you ever get run into by fish?" The short answer is, "No, not really." But we have had some very close calls.
Little fish, like the fast-swimming Fuslier Fish we showed you recently, often approach in a large school, and at a high rate of speed, but they manage to steer en masse around obstacles -- including divers -- by making high-speed turns in unison, or simply by splitting the school for a moment, with half the fish passing on each side of the diver. Once past the obstacle, the fish reunite into one school again and continue on their way.
Other kinds of small fish that form dense schools do more hovering than swimming around. Sometimes a diver will encounter a dense school of Sweepers or Glassfish hovering in an underwater canyon, or even inside a shipwreck or a cavelet. As the diver (or a large fish) swims toward the apparent wall of little silvery fish, they may scatter. More often, though, the school simply parts like two halves of a stage curtain to allow the bigger swimmer to pass through, then closes again afterward. It can be an amazing sight, and an almost dream-like experience.
In sum, smaller fish usually get out of the way of larger fish and divers, one way or another. Now let's talk about larger fish -- much larger fish.
Over the years, we have noted that the larger the animal, the more likely it will notice divers and even come close to have a look. On occasion they come very, very close.
Consider the photo at right: that's a Whitetip Reef Shark (Triaenodon obesus). I first saw this particular shark while it was about 75 feet (23 meters) in front of me. It was coming toward me at a leisurely pace, so I settled into position and aimed my camera, hoping it would come close enough for a good photo.
Through the viewfinder I watched it come closer and closer, heading straight at me now. It had spotted me, for sure.
About two seconds before I snapped the shutter for this shot I thought I might have to duck out of the way, because the shark had now picked up speed a bit and I feared it might bump into me, head on. I knew it had seen me, so it was starting to feel like a game of chicken! Then at the last moment, the shark made a sharp right turn directly in front of me and swam off (as if that had always been what it had intended to do!), avoiding a collision.
This was neither the first nor the last time that one of the larger species on the reef had intentionally come right up to one or both of us to look us over, and made a very close pass. In fact, sharks and barracudas often do this. So do large groupers, wrasses, jacks, and every kind of marine mammal we've ever been with in the water, including dolphins and whales. (Long-time readers of The Right Blue will recall our tale of close encounters with humpback whales.) But none of these cases ended in a collision, either.
On the other hand, we've had, or witnessed, quite a number of very close calls -- near-collisions with big critters in the sea. Usually this happens when two critters, or rather a critter and a diver, round a corner or swim over a rise at the same time from opposite directions, unaware that the other is approaching until they nearly collide.
Another scenario for close scrapes occurs when a diver inadvertently startles an animal, and the animal reflexively attempts to escape the scene. Once, while diving with a good friend and a visiting diver, we took the visitor to a place where we knew Whitetip Reef Sharks went to rest. The spot was a sheltered cavelet in the face of an underwater cliff. We approached carefully from below the cavelet and quietly positioned ourselves so that we could peek inside. My friend shined his light onto the ceiling of the cavelet, so that the light reflected down just enough for us to see two sharks 'sleeping' inside. The visitor, wanting to get a better look, shined his light straight into the cave, right into the face of one of the sharks. The shark startled and shot out of the cavelet like a missile, grazing my friend's head on the way, and knocking off his dive mask in the process.
On another occasion, Jerry and I passed below a ledge where drowsy sharks sometimes lolled. I was in the lead, with Jerry following just a meter or two behind me. As best as we can reconstruct what happened, we think my exhaled air bubbles must have passed by a shark on that ledge and disturbed it. It was another 'missile launch' situation, but this time the shark swam between Jerry and me, and as it did, it passed right in front of Jerry's face. Reflexively, Jerry's arms shot forward and he shoved the shark. This shocked the poor shark even more, and it sort of jack-knifed sideways. By this time I had turned around, and now the shark went berserk, probably thinking we were trying to corral it. It swam around frantically in a very tight circle for two or three revolutions (like a puppy chasing its tail) before it saw its opening and catapulted itself from between us and went careening down the reef. We stared after it until we could no longer see it, our hearts pounding from the unexpected excitement on an otherwise tranquil and leisurely dive.
Here's one more photo from a near-collision we had with a large stingray. From a technical point of view, it's a lousy shot, but I'm posting it anyway because it has such an interesting story.
We were on a deep sandslope, where I was shooting macro photos of small creatures that inhabited the nooks and crannies of a large, irregular rock. We were both crouched over the rock, engrossed in the task. Jerry looked up briefly, just in time to see an Amberjack swimming up the slope, heading right toward us. Jerry nudged me and pointed toward the Amberjack. I turned my head to look, and noticed that there was another, darker creature moving along the sand, beneath the Amberjack. In one of those 'lightbulb' moments of comprehension, we instantly recognized that we were witnessing a rare sight: a large deep-dwelling stingray species hardly ever seen by divers. Even though my camera was set up for macro, I whirled around and snapped this one shot, just as the Amberjack veered away, and the stingray sort of skidded to a stop, touching me, but just barely.
What looks like snow in the photo is light from my camera's strobe, reflected on sand particles that the stingray and I had stirred up at that moment. An instant later the big stingray did an urgent about face, stirring up a huge cloud of sand particles as it quickly retreated back to the depths.
In case you are wondering about the stingray, it looked to be about 1 to 1.5 meters across. It is either a Hawaiian Stingray (Dasyatis brevis) or a Brown Stingray (Dasyatis latus), but the photo is not clear enough to determine which it is with certainty. Both are known to inhabit deep sandy areas in Hawaii. They are uncommon around reefs, so they are rarely seen by divers. This was one of only three or four encounters we have had with one of these stingrays in all our years of diving in Hawaii, and this was the only time I got to photograph one.
Tuesday, June 3, 2008
Monday, June 2, 2008
Fusilier Fish: Speed Demons of the Reef
This is a Right Blue photo essay on Fusilier Fish (Caesionidae). These fish, which move about a tropical reef in large schools, always seem to appear suddenly and out of nowhere. In unison, they zoom first one way, and then another, at speeds that can make your jaw drop, doing precision turns that leave those watching in awe. For divers, encountering a school of Fusilier Fish always is exhilarating. I hope this series of photos, which I took in quick succession, will give our readers a sense of what it's like to encounter a school of Fusilier Fish.
Here they come.
Then they do an about face.
Then they circle back again.
And then they're gone!
[Click on any of the photos to enlarge.]
Tuesday, May 27, 2008
Tuesday, May 20, 2008
Sunday, May 18, 2008
Have you ever seen a pregnant shark?
Someone we know saw a TV program about sharks, and learned that while some shark species lay eggs, others give live birth. He asked us, "Have you ever seen a pregnant shark?"
Yes, we have seen pregnant sharks, and I even managed to photograph one. At right is a photo of a pregnant White Tip Reef Shark (Triaenodon obesus) that I took at Sipadan Island, off the coast of Borneo. She looks like she is about ready to pop! [Click on the photo to enlarge.]
This species is known to breed in the Autumn and Winter. The gestation period is thought to be about five months. Whitetip Reef Sharks give birth to litters of two or three pups.
As soon as the pups are born they are on their own. The mama shark does not look after the pups in any way.
As a comparison, here is another photo, taken on the same dive. This second photo shows a human observer with a White Tip Reef Shark that is not pregnant. As you can see, individuals of this species are rather slender and sleek -- torpedo-shaped. The poor pregnant female above looks ungainly in contrast.
By the way, this location at Sipadan was a shark-lovers' paradise. We had never before (nor have we since) seen so many sharks in such a small area.
There were big sharks, little sharks, and medium sized sharks of assorted species. There were sharks swimming, and sharks lying on the bottom resting, sometimes lined up in rows like parked cars.
And there was one pregnant shark!
Tuesday, May 13, 2008
Wednesday, April 30, 2008
Tuesday, April 29, 2008
What Brutus the Great Barracuda Saw
In the previous post I wrote about a Great Barracuda named Brutus who liked to follow Jerry around the reef at Puako. If you read that post, you'll recall that after a few experiments, we concluded that the big fish actually was attracted to the yellow sleeves on Jerry's wetsuit, probably because the color stood out so well against the background, compared to the black and dark blue suits the other divers in our group were wearing.
Today I was looking through some recently scanned photos, and by chance I came across this nice shot of Jerry with a school of Horse-eye Jacks. I took it with natural light -- no flash -- at Providenciales in the Turks and Caicos Islands. Looking first at the thumbnail, I thought, "This looks like a Right Blue photo." But when I enlarged it on my monitor, I knew instantly: "THIS is what Brutus saw!"
See what I mean? (Insert 'big grin' emoticon, heh heh.)
[Click on the photo to enlarge]Friday, April 25, 2008
Remembering Brutus, the Great Barracuda
You would think that after doing thousands of dives at hundreds of dive sites around the world, we would not remember encounters with individual fish. Who knows how many different fish we have seen in our long years of diving? Yet there are a few individuals among the masses that do stand out in our memory. One of those was a big silvery fish that hung out near our home reef at Puako, Hawaii for the better part of a year.
That big silvery fish was a Great Barracuda (Sphyraena barracuda), just like the one in the photo at right. I photographed that one in the Caribbean, but we have seen this species all over the world, and have had many close encounters with them. Most of our encounters with barracuda were unremarkable, until we crossed paths with the one we came to call Brutus.
Brutus the Great Barracuda was 'great' in more ways than one. He was great in size: we figured he was about five feet long and probably weighed around 70 pounds. He also was a great companion: if he spotted us from a distance he'd hurry to us, and then follow us around for most of our dive.
Seeing a big barracuda like Brutus underwater can make the hair on the back of a diver's neck stand up and prickle, but Brutus never harmed us, nor did he ever give any sign that he wanted to do anything more than watch what we were doing. In fact, he could be downright nosy.
Usually Brutus followed us at a respectful distance of, say, 20 to 30 feet. But there were times when we'd stop to look closely at some tiny little creature, and that distance would close until we'd have Brutus looking right over our shoulders. I don't know why he did that. Maybe he thought we might have found something good to eat, and he didn't want to miss it. What I do know is that sometimes we'd turn our heads, and there would be this big barracuda face with the gnarly-toothed grin right there!
When Brutus first started to follow us around, we thought maybe we were imagining it. We thought maybe the big fish just happened to be going where we were going, and was not really following us at all. So, along with our friend Dan, we cooked up an experiment: We agreed ahead of time that if we saw Brutus and he started to follow us, we would reverse direction, swim past him, and see if he then turned around and stayed behind us. He did. After a few more rounds of this we concluded that he really was following us intentionally, and not by chance.
Then we noticed that Brutus seemed to prefer Jerry to Dan and me. When the three of us were diving together, it was our habit to swim more or less parallel to one another, but about 15 or 20 feet apart. We noticed that when we fanned out like that, Brutus would watch all of us, but seemed to follow Jerry more closely. So, we planned another experiment. On one dive, Jerry would be positioned in the middle, with Dan and me at either side. On another dive Jerry would take an end position, and either Dan or I would take the middle spot. Sure enough, regardless of which position in the line-up Jerry took, Brutus would be right behind him.
What was it about Jerry that attracted this big barracuda? The probable answer came one day when I stopped to look at something, while Jerry and Dan swam ahead. When I looked up to see where they were, I spotted Jerry right away. He was wearing a wetsuit that had bright yellow sleeves, and had on yellow fins, too. The yellow was very visible, even from a distance. I couldn't see Dan until I got closer. Dan's suit was all black, just like mine. It was one of those 'lightbulb' moments. "Aha!" I thought. "That's it!" It probably was the yellow in Jerry's dive attire that attracted Brutus.
Barracuda are believed to be attracted to shiny things, probably because much of their diet consists of little silvery fishies. It occurred to me that, while Jerry's fins and wetsuit were not shiny, the yellow color definitely stood out in contrast to the background. You know what's coming, I'll bet. One more experiment.
The next time we went diving, Jerry and Dan swapped suits. Jerry wore all black, and Dan now wore the suit with the bright yellow sleeves. Along came Brutus. We fanned out across the reef, with Dan in the middle, dressed in Jerry's suit. Just as we had hypothesized, Brutus now followed behind Dan. When they switched positions, Brutus still followed Dan. We concluded that it was indeed the yellow in the suit that had attracted the barracuda. After that, we referred to that suit as Barracuda Bait!
So, if you're diving in waters where there are Great Barracuda about, and you don't want to attract their attention, do not wear a high-contrast outfit underwater. Wear a suit that blends, not one that stands out. Don't be barracuda bait.
Wednesday, April 16, 2008
Wednesday, April 2, 2008
Wednesday, February 13, 2008
Tuesday, February 12, 2008
Do Not Disturb: Sleeping Fish
We all need our rest, and so do the fish in the sea. Fish don't sleep exactly like we do. For one thing, they don't have eyelids, so they can't close their eyes. Nevertheless, most fish we know about do take their rest for some part of the day or night, on a fairly regular schedule.
Some fish -- especially pelagics -- hunt at night, and rest during the day. Most reef fish are very busy during the day, so they rest at night. They stop moving about and enter a sleep-like state. While they are resting, they are generally sluggish and not very alert. We try our best not to startle them or disturb their rest during our night dives.
Some fish lie on the bottom to rest, while others hang motionless in the water column. Small fish, in particular, often hide while they are in their somnolent state so that their predators can't find them and eat them. Staying out in the open to rest definitely would give their predators an unfair advantage. In the first photo on this page, a tiny fish called a Pygmy Toby (Canthigaster pygmaea) has snuggled itself amongst corals and sponges to "sleep."
In the second photo, a small fish has chosen to settle into a stand of fire coral to takes its rest. We're not sure what species of fish this is, although the shape suggests that it is some kind of Damselfish.
In addition to hiding, another strategy that many fish use to discourage predation while they rest is to change color. Their color may darken or become mottled during periods of rest, helping them to blend in with their environmental background.
Some species of Parrotfish hide themselves by spinning a slimy cocoon around themselves. The mucous cocoon is secreted from an organ in the head of the Parrotfish. (Sorry, I don't have a photo handy.) It is thought that, in addition to hiding the fish, the cocoon also masks the animals' scent, making it harder for predators to locate them.
Both of the images on this page were captured during night dives in the Red Sea, along the coast of the Sinai Peninsula.
Monday, February 11, 2008
The Leaf Scorpionfish
Meet the Leaf Scorpionfish (Taenianotus triacanthus). This little fishie is one of the smallest members of the Scorpionfish family. This fish family, Scorpaenidae, gets its name from the venomous spines that most of the fishes in the family bear. (Regular readers of The Right Blue will recall our posts about the Turkeyfish/Lionfish -- another member of the same family.)
The Leaf Scorpionfish gets its name from its appearance. When you see one in its natural environment, it really does look like a leaf, rather than a fish -- until you spot its eye! Members of the Scorpaenidae family tend to be "lie-and-wait" predators. They tend to stay still in one spot until their prey happens past, and then they pounce very suddenly. They rely on camouflage so that they can blend into their surroundings, making it easier for them to surprise their prey.
The bodies of Leaf Scorpionfish are laterally very flat, which certainly contributes to their leaf-like appearance. This little fish not only looks very much like a leaf, it also behaves like a leaf! If you stay still and watch one for awhile, you'll see the little guy rock back and forth every once in awhile, just as a leaf or a stray piece of seaweed would do if it had settled on the reef. This, too, seems calculated to trick potential prey.
The Leaf Scorpionfish is a small species -- maximum length is about four inches (10 cm). They come in lots of colors -- yellow, reddish, purple, brown, pale pink, and off-white. They often have blotches, which enhance their camouflage, and they sport little fleshy appendages on their heads and chins that look like little weeds growing on them.
The photos on this page show examples of some of the color variations of the Leaf Scorpionfish. Despite the range of colors, they are all the same species. (Click on the photos to enlarge.)
The first photo on this page shows a purple Leaf Scorpionfish. You can see that this individual has a lot of blotches. If you see a scuzzy-looking Leaf Scorpionfish, he's probably getting ready to molt, which they do periodically. Soon after they molt they look much less blotchy. Sometimes the color looks a bit different after molting, too.
The second photo is a 1:1 macro shot of a Leaf Scorpionfish that we watched over a period of many months. In the second photo, you can see the little fleshy appendages on the fish's chin quite clearly. It's all part of the disguise.
We've noticed that when one of these fish finds a good spot on the reef, they tend to stay put in the same small patch of real estate for a long time. Once one is located, it's a safe bet that a diver will be able to return to the same spot again and again, day after day, month after month, and see the same little fish. Good dive guides know this, and that is why they can reliably lead divers and underwater photographers to a Leaf Fish almost at will.
The final photo on this page shows one more color variety. This yellow Leaf Scorpionfish is perched on a coral head. We have noticed that smaller Leaf Scorpionfish often tend to hide in the coral this way, while the larger ones seem to prefer a spot on a rocky bottom. We don't know why this is so, but we surmise that the little ones may feel safer in the coral, since it affords them some protection. They can hunker down if there's a lot of surge, for instance.
I took all of the photos on this page at Puako, Hawaii, at depths ranging from less than 20 feet (6 m) to about 125 ft (38 m).
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