Fish staging in one spot

Went perch fishing today, and we found them in two brush tops next to the bank, and the brush tops was close to an intersection like a  T. 

We fished up, and down the canal.  We caught 60 fish out of the two tops. We didn't catch fish anywhere else.  We were using shiners. 

The middle of the canal is about 9ft, a boat lane is what it is, but the water was about 5ft deep at the brush tops.

All the females were full of eggs, so I guess they are getting ready to move to the shallows, and bed up.

Why were the fish in just two spots ???

Thanks,  RP