Squid shoaling: why some do it and others don´t?

[Jose]

Hi!
There are several examples of squid species that shoal, usually linked to major fishery activities (e.g. Illex sp. fisheries). However, it is not clear why some species do it (e.g. some loliginids and some Omastrephids) and others clearly don´t (e.g. some Onychoteuthids, some Histioteuthids, etc).

My query.... is there a review out there assessing this issue and if any authors questioned what could be the driving factors of this different behaviour (e.g. being coastal, food availability, morphological aspects).

Obrigada!

 

[main_board]

I would see this as akin to fish; some species are hardcore schoolers and some wouldn't know what to do is a school. As each species has evolved, they've found a niche in their ecosystem that works for them and in some places this means schooling and in other not. Thats just what I think and know, though I do look forward to seeing some scientific view of the same problem. I'm sure that there's much more to it than what I've mentioned, nothing in nature is that simple.

Good question!

Cheers!

 

[Fujisawas Sake]

Great question!

I would guess that their external functional morphology would be dependent on their swimming behaviour, which would include schooling. I'm not too keen on hydrodymanics, so I don't know if there is an energetics issue with squid schools analogous to bird flight formations, but that may be the case.

I have a paper on squid geometry and speed, so I'll see if there are any references to this question when I get home.

As to why some squid school and some don't... Well, I don't mean to sound dismissive, but I think its just a product of ethological variation in the Teuthids. There probably is an actual overall reason why, but I wouldn't risk surmising it at this point since I'm not even CLOSE to qualified to answer that.

Once again, GREAT question.

John

 

[Tintenfisch]

Plus some of the species that don't normally live in groups do come together into spawning aggregations that could, loosely, be termed temporary shoaling or schooling.

 

[Steve O'Shea]

A very good question, Jose! I have no answer, nor am I aware of any review undertaken on this aspect of behaviour/biology. It could well have something to do with depth of habitation (as subadults and adults; the juveniles of deep-sea species can occur in the upper few metres), and food availability/water-column productivity (usually shoaling/schooling near a convergence in water masses, most likely to release egg masses, or deposit egg masses in highly productive areas so that the paralarvae have an abundance of food).

Are you absolutely sure that neither histioteuthids nor onychoteuthids shoal? Probably partial support for some form of shoaling behaviour (it's a matter of scale) in these two families, at least as spawning adults, could be obtained from stomach content analysis of predators, chiefly teuthophagous cetaceans.

 

[Euprymna]

Very intersting!!

Since schoaling could imply mating aggregations, which is different
from normal schoaling behaviour. We should distinguish which schoaling we are talking about.
In the "normal" schoaling case, I would guess that the main reason explaining its appearance (at least in evolution of teleosts) is as a defense mechanism against predation. Hence, the answer of why some squids schoal and some dont, may lie in the pressure excersed by their predators which surely differs between areas and species.
Im not a behavioral ecologist but give just a thought