Why the shark matters
If the shark reaches your catch, you lose the fish and any island income it would have generated. The shark is the dominant failure case in late-game runs.
Cast skill is the real defense
Higher cast skill gives you a longer reaction window before the shark reaches you. Train cast BEFORE going for rare fish, not after.
Rod tier changes the math
Better rods widen the cast window so the shark approach is slower. Crow / Ice / Thunder each add meaningful escape margin.
Gamepass help
The x2 Fish Luck and x2 Pull Power gamepasses help you re-catch faster if you do lose a fish. The x2 Cash gamepass helps you recover coin reserves.