Your rivers are doing some unnatural things. In almost every case, you have rivers that traverse the entire island, despite being right next to the sea near the source. On Tapu Tapu the rivers are even crazier. You've got rivers that connect to each other, then breaking into dozens of smaller rivers going to the sea - which is impossible. Think of a river as a tree. The trunk is the widest part of the river, the part that reaches the sea. Smaller rivers can join like branches from their sources to the main trunk. You ought to visit our How to get your rivers in the right place thread in the How-To forum.
Another thing to consider is that most islands don't support rivers. Of the Hawaiian islands, for example, only the island of Kuau'i feature rivers - it has 3 rivers, but then Kuau'i is one of the rainiest places on Earth. All of the other islands of Hawaii feature ground water reservoirs under the surface, but no actual surface rivers.