Can a conservation officer make a BWI arrest if he comes across an intoxicated boat operator? Yep....and they will.
Are they out checking creels as a guise to make BWI arrests? Nope.
Actually, a conservation officer, in the course of his duties, could (while on patrol in his vehicle) make a DWI arrest under the appropriate conditions. However, it happens very rarely and as has been pointed out they would most likely call in the appropriate law enforcement agency to take over the arrest.
Bottom line? Conservation officers routinely make creel checks and issue the appropriate citation upon discovering a violation because that is what they are trained and empowered and expected to do. They also make an occasional arrest for a secondary violation when the opportunity presents itself, not because of some nefarious sublot but because that is what they are trained and empoered and expected to do!
In retrospect regarding intent both Kamper & Nightwing are correct...