Powder blues schooling...Video.

[Simon Garratt]

I recently took this footage in the Maldives and thought you guys might like it.

I tried finding footage online but came up blank so I thought Id take a video whilst i was out there.

Acanthurus leucosternon schooling


They were so engrossed in feeding that i just dived in amongst them and sat there, on occasions they would actually butt the camera or brush up against my hands. This footage was shot on the seaward side of the reef flat. whilst the back reef was home to territory holding pairs.


Note the damage to anterior dorsal and anal fins through agression within the group.


regards

 

[straightjiggy10]

nice

 

[KathyC]

Simply amazing, beautiful sight. Thanks for sharing Simon

 

[Awibrandy]

Absolutely beautiful!!! Thank you thank you thank you!

 

[House of Laughter]

Brilliant

Did I see some bristle tooth and parrots mixing it in there? What on earth are they eating?

House

 

[Simon Garratt]

I couldnt ID the exact species, but yes they do tend to group with a small dark tan coloured parrot fish species, and they commonly have a number of Ctenochaetus striatus mixed in with the group,

They generally feed on fine light brown turf algaes and other low growing algal films. In fact they seem quite specific. often ignoring taller growths in favour of the shorter types. They also seem to like turfs that have a high degree of trapped or accumulated base sedimentation. I have a hunch that this is where they get much of the additional nutrition they need by way of incidental microfauna uptake that inhabits these mucky areas around the base of the algaes. Ive seen some gut analasis surveys and the % of non vegatative material can be quite high, consisting of quite a high quantity of copepods etc and other microfauna.

regards

 

[lunner]

Thx for sharing. Nice video

 

[Aqua Pro Builder]

In some other footage I saw, powder blue tangs seem not schooling type of tangs and even try to fight off other kind of schooling tangs that hurried in/out or their territories after feeding. So can you please describe further when they will school and when they don't?

 

[Simon Garratt]

Hi, strangely enough the same conversation cropped up on another forum that i posted the video on, so Ill copy over the whole conversation so others can participate (and to save me typing it all out again) lol.

I've seen similar many times in the Maldives but nowhere else. I still don't really understand why they can shoal in the wild then turn into cage fighters in captivity. Is it a food issue rather than territory, which is usually a sexual/breeding thing is it not?

Rod

Hi Rod.

Its quite a complex subject to be honest. The behavoral traits of this nature in tangs are commonly dictated by four factors..

Food availability.

Breeding status.

Territory availability.

Predation.

The very short version/theory that I hold to after looking through various research on territory and breeding behavour, is that the schools (which havent been studied) are simply the population overspill.

Its usually the case that much of the back reef areas are taken up by territory holding pairs with territories that butt up against one another to nearly 100% saturation levels within an applicable zone that has geographical markers for territory formation and a viable food source within those individual territories (the food sources are quite specific and the two must be combined)...this leaves the rest of the non paired population in a bit of a predicament....As an individual, you stand little chance of getting into the territory of an existing pair to take advantage of the required food source, plus you are more likely to suffer predation. So the next best tactic is to lower your agression levels, become more sociable and join a raiding party that can barge into these areas to overwelm the existing pair and steal the food source, and thats exactly what you see out on the reef and why certain locations have schools whilst others dont..Its simply a factor of how well that species is doing in the face of other factors...available territories, available food, and lack of predation giving rise to a higher population density...The schools are imo representative of that balance...

The problem with trying this in a closed system is that you imediately introduce fish to a territory that is open to habitation, so the most dominant fish will imediately try to take charge and settle...the group is then seen as a threat from that point onwards as it would be in the wild...

regards
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Simon Garratt. o.c.r.d​

You sure about your statement when I witnessed it, it appeared all tangs in a large surrounding area gathered together in the shoal in want appeared to be a feeding fenzy, there was no pairs for a considerable distance

spshoover

I honestly cant answer that Si.

I cant see any reason why a territory holding pair would leave thier area to mass group with other pairs for the sake of a quick snack. It leaves the territory open to competitors in thier absence and they wouldnt take on a territory unless it had a food source within its boundries.

It may simply be the case that in the situation you whitnessed there wasnt the right combination of geographical markers and correct food source on that section of reef to induce full blown territory formation. In that situation you could quite feasibly end up with an area that has no defined territories and a wandering spread population that rely on communication or recognition of behavour in another individual to spot when a patch of the correct type of algaes are found....ie, they all wander around as a very loose group, and when one spots the food source, its behavour triggers a knock on effect that draws others together.
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Simon Garratt. o.c.r.d​

To highlight in pictorial terms.

If you look at these two images you'll see ive highlighted the terrirtory holder who rises up and out from the center of his/her spot to meet oncoming competitors, (in this case a passing school) in both instances the territory holder was showing good warning signals to the passing group in a bid to stave off any interest in his/her patch (second shot with highly errect dorsal and anal fins). The territories can be quite large in some instances spanning a good 20ft in radius from a central point or geographic marker (In the second shot you can see a large boulder that formed its base).

__________________

Simon Garratt. o.c.r.d​

Si G

Your explanation does make sense and does fit what I have seen. It may also be partly geographic I suspect, as in the Maldives as I'm sure you know, the islands and reefs can be quite small, and not able to support such large shoals permanently. Maybe this shoaling behaviour is a practical way of moving between the islands and reefs in the atoll as a whole, as moving between reefs through open water without the protection of a shoal would be suicide for something as noticeable as a powder blue tang. I have dived in many areas around Asia mainly but haven't seen these larger shoals anywhere else, could be coincidence of course.

Rod

Very true Rod and it harks back to a conversation I had with Julian Sprung out at macna after his presentation on hybridization.

As a hobby we commonly think of mother nature as some sort of giant printing press, shunting out carbon copies of the same species again and again without realising that sometimes you get glitches. the triggers for these glitches can be numerous, as are the long term results, be that a short term single individual or the forming of a new long term species.

The same factors apply to behavour. Whilst certain traits are genetically engineerd into each species as a bench mark, they are not infalable nor inflexible in most cases. A population of a given species may over time change behavours subtely to adapt to local conditions differently to the same species in a different geographical area.

Hence so many differing opinions.

regards
__________________

Simon Garratt. o.c.r.d​

Thats about as far as the conversation got, so if anybody wants to chip in...its always worth further comment / investigation.


regards

 

[isgon26]

Now if I could only keep one in my tank without getting ick or dying.

 

[Awibrandy]

Now if I could only keep one in my tank without getting ick or dying.

I hear ya! Same here.;(

 

[masterswimmer]

Simon, thanks for sharing such a beautiful act of nature. Must have been amazing diving within that frenzy.

Russ

 

[dickenscd]

Simon,

Please give me a call when you go to your next diving.

James

 

[lindsay]

Amazing..

 

[Thatguy96]

I have had trouble keeping this fish