On Mon, 08 Jun 2009 23:37:06 -0500, Richard Casady
wrote:


When I was kid, swimming in an Iowa lake, we would occasional a dense
ball of inch and a half bullheads, catfish they are. Two foot diameter
roughly a ball. So when I read a reference to a bait ball I knew what
it was like.

They showed one on 'animal snuff'. The tuna showed up and it was gone
in two and a half hours.

Someone gave us a ball of leopard frog tadpoles: one sweep of the net.
Papa was watching them. We dumped them in water too shallow for the
bass. We already had leopard frogs. so they will be OK maybe,but
without father to protect them from the other frogs.

So why do fish form dense balls? So an orca can eat them all real
fast?

There are several schools of thought regarding bait balls.

The first theory is that it's a defensive mechanism in that the bait
ball appears much larger thus presenting a large "thing" that will
deter attacks and predation.

Another theory has it that predators will herd the bait into a ball
and then bust the ball in a feeding frenzy or pick off the outl layers
at leisure.

A third theory suggests that it's a panic behavior on the part of the
particular target species - a sort of concentrating strengths until an
an escape path is presented.

Personally, I think it's a combination of theories. In my experience,
with tuna in particular, I've seen large schools of tuna herd loose
schools of mackeral and herring into a more concentrated area, then
just bust through the ball in speed attacks. The interesting feature
is that the tuna themselves will essentially build up an outer wall
around the bait ball then individual tuna will peel off, bust the
bait, then rejoin the surrounding wall. It's very interesting to
watch.

I've seen it happen with freshwater fish - in particular largemouth
bass who will often pin a school of minnows against a shore line or
rock wall - usually two or three fish and they will patrol the edges
of the minnow school waiting for the eventual one or two try to break
out and the bass can pick them off at their leisure.

With respect to orcas, I would think that it's done, but I don't know
of an instance where it's ever been documented. I do know that
dolphins, a orca cousin if you will, will hard bait into balls and
have at it. It dolphins do it, it makes sense that an orca would too.

I poked around on Youtube and found this.

http://www.youtube.com/watch?v=r1m6IKiO26c