Aerial survey over the sea is usually for environmental reasons and or prospective off shore wind farms. Off shore wind farms may as part of planning process/authorisation want sea bird surveys. Believe it or not they count birds floating on the sea from the imagery as well as other things.
Survey flight lines, depending if for lidar or imagery, will align with various things - wind direction to lower crab angles even with gyro mounts which can handle certain crab angles, terrain heights to minimise GSD fluctuation (and avoid need for 3D flight plans that have a lot of flying height changes) and terrain (or infrastructure) alignment - i.e. roads or coastlines.