Sorry, only found this thread now!
I was up at Mtata during Easter. My bro and I got spooled several times my big(10 - 20kg) kob right in the river, near the mouth at night. We were fishing big rapalas with very very slow retrieves, on light line(probly why we got smashed so often). The water is dirty, so kob are ussually around.
We did manage a few smaller fish. (1 -3kg), but they just dont compare!
There were also small barracuda in the river, and shad were plentyful around the rocks.
Keep an eye out for shoals of yellowtail feeding just offshore. We saw them, but never once had them in range.