Fishing can be a test of patience. If you need to spend multiple days out there, then you better take reliable piece of shelter with you. There are plenty of 2 man bivvies that should keep you and your mate comfortable while camping.
Look for adequate space including floor space and ceiling height. Make sure that there are vents for good airflow. You never know if it is going to rain so check whether the bivvy is waterproof or not. This will prevent you from getting drenched inside and potentially spending nights shivering in the cold.
The frame should be of high quality. It should be able to keep the structure in place despite strong winds and heavy rain. On the other hand, it should be light and small enough when folded for portability. Read reviews to learn about their real-world performance.