I don't have surf or any rod except the old rod, and I checked those routes and Dewford and there is no grass, only fishing Pokemon, and I've already caught all the ones it says are there for the old rod(Tentacool and Magikarp) Am I missing something?
This is because you get Wailmer with the Good Rod only. Also, there are Pokemon you can obtain by surfing. There are also hidden encounters you can only access once you've defeated or captured Groudon or Kyogre.
Route 106's full list of Pokemon
Route 107's full list of Pokemon