Saturday, October 21, 2006

21st October 2006

weather: sunny all day
sea condition: calm and flat vis: 5 - 15m

Guides: Sophia, Jay, Bobby, Su

The weather today is just like!! Makes everyone here wanna just jump in the water!! It's full moon today, and just like every other new moons and full moons, we could anticipate to see that the fish are more active than usual and more fishes comes out during this time. Especially the school of barracudas and grey reefs sharks.

Some of us may wonder why does the barracudas, jack fish, bumphead parrotfish, snappers etc. always group together? They are a few reasons why they like to stay together in a school.

One of the reason is that they will gain more efficiency when they are hunting in a school. If we look closely, the fish in the school are placed from each other at similar distance from each other. This is to make the prey easier to catch by aligning themselves in distances which is approximately the distance that the prey fish will typically move to avoid the hunting fishes. In this way, the whole school will benefit from this behaviour to travel together in school.

Another reason is the opposite for the above reason, which is to avoid being hunted by other predators. When they travel in school, their chances of detecting a predator will be increased and the whole school will be alarmed easier whenever there's a predator nearby. And when this happens, the whole school will swim away together, thus diluting the predator of where the school is heading and eventually will increase the chanc for them to escape from the predator.

The third reason will be to increase the fishes' chance to find a mate to reproduce. Often we can see that the fishes in the school are of similar appearance and size and body colour. This is to make the school more homogenized so that no individual fish will stand out in the school. Think of this as..."Everybody's the same, so why choose him over me? We are all the same, no need to look for a better looking fish than me! Let's reproduce!!".

And another possible explanation is that the fishes can travel together with less energy consumption. It is suggested from studies that when they travel in group, they use less energy by taking advantage of the pressure field created by the other fish that could deflect the effect of the water force that hinders their movements. If we observe close enough, the school of fish most often travel in the direction against the current. Very seldom will the school of fish swim in the same direction with the water current. That's one of the reasons why we always drift with the current in Sipadan rather than going against the current.


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