It’s coming up to 25 years since I made
this underwater observation off the coast of peninsula Malaysia. Until recently, I simply assumed it was a shoal. Until, that was, I read this definition in
a 2012 paper posted at the University of Zurich open repository:
Shoal (shoaling): Formation of a relatively nonpolarized group… held together by social pressures (i.e., not by individual attraction to an external stimulus).
I had also recently read a 1973 paper noting that:
In coral reef fish communities we find several species foraging in the water column from a “home base” on the reef within a relatively restricted habitat or home range.
Okay, so the density of fish suggests a social mechanism. But perhaps each is attracted to its own individual micro-refugium (its own apartment) in the staghorn coral complex. Short, close forays to externally located and stimulating food particles drifting in the current will then coincidentally aggregate fish.
What do you think? Is this an actual shoal, or just a coincidental clustering effect of colonial home-basing? Or something else?
Not a fish biologist but they could be considered as shoaling. They’re not schooling since they seem to be each doing their own thing ( not heading in same direction in coordinated way). Or they’re all just hanging out in good habitat with no social involvement.
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That’s where I started. But I think the definition quoted questions it. I agree about them not schooling - they are not at all polarized.
Looks like shoaling. Is it one species or several?
@DitchingIt Peter is a fisheries biologist. Can you remember well enough, from 25 years ago, to answer his question?
It’s a single species in which adults hide in high density colonies in staghorn coral clumps at night or when threatened. (Juveniles often join clownfishes in anemones which is interesting by itself.) Would you disagree with the 2012 definition offered, or am I misinterpreting It’s caveat about attraction to an external stimulus?
The definition is pretty standard. Aggregations like this may be exclusively habitat related but generally that would lead to randomly distributed individuals within the habitat. Social interactions can also lead to randomness (or quasi-randomness) but clumped or uniform distributions are strongly suggestive of social interaxtions, hence shoaling. In reality, the social interactions usually happen alongside externally mediated behaviour.
Absent appropriately designed, controlled experiments or Bayesion modelling of observational data you can only make an informed guess. This photo appears to me to be fish shoaling. The absence of other species is consistent with that interpretation. It could just be fish hanging around but that density of fish in one place would be pretty unusual if there weren’t social pressures over-riding agonistic behaviours.
Schooling is usually more or less straightforward to identify. Shoaling less so.
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