The only way to know if calibration has changes is to calibrate the full system before and after deployment. This can be done for a single frequency, e.g. 2 kHz and has not to be done for the whole frequency range.
Edit: this can be done even in air: have a time with same amplitude be played to system before and after deployment keeping same geometry.
Edit2: this applies also to hydrophones, even if sensitivity is not as high as in water, but for the OP (changes in sensitivity) only the difference matter.
Edit3: Obviously, using a single tone only implies that changes in sensitivity are not spectral but effect whole spectrum in the same way, Otherwise multiple tones with different frequencies are required.