My guess would be that it wasn't fish related; perhaps it might be
nervousness from predators, compounded by mob mentality. If it were related
to schooling fish I would expect other species to be involved: cormorants,
gulls, etc.
Wayne Potts did a Master's degree study on flock movement in dunlin, finding
that any bird on the periphery of the flock could manipulate the flock's
flight direction if it turned in toward the rest of the flock. With high
speed photography he pinpointed which individuals initiated changes in
flight direction.
The merganser reluctance or inability to fly does make for a very striking
scene! Water aerobics?

Kevin Li
Seattle WA
> ----------
> From: Leslie Ann Rose[SMTP:sylph at nwlink.com]
> Reply To: sylph at nwlink.com
> Sent: Thursday, September 03, 1998 7:04 AM
> To: tweeters at u.washington.edu
> Subject: Re: Nisqually sightings
>
> What follows is PURE speculation. Wonder if it has anything to do with
> feeding? Does anybody know if there has been a hatchery release
> recently further upstream? Perhaps a run of other small species of
> fish? Or perhaps they were playing Follow the Leader?
>
> LeslieAnn Rose
> Tacoma, WA
>
> Kelly Mcallister wrote:
> >
> > Kevin and Tweeters,
> >
> Somebody please tell me what is on the minds of those mergansers. I was
> stationed on the beach on the east side of the Nisqually River mouth
> (below railroad tracks) today and I estimated the flock of Common
> Mergansers to be at least 300, perhaps 400. But, they are possessed.
> They act as though constantly in some kind of race to get to the next
> location which appears to be a more or less random choice of direction.
> But the don't fly, oh no, that would be cheating. They skuttle as fast
> as they can under leg power, with necks stretched forward, churning a
> great wake from behind. Once they cross the great Nisqually Reach, they
> appear to have little better to do but turn around and head back. This,
> all in a group.
>
>