What is the difference between Deep water and Shallow water sensors?

The Deep water Sensor System is rated for use in water at depths greater than the Shallow water Sensor System. More specifically:

The  Deep water Strain Transducer is waterproof to at least 300 m (~1,000 ft.) for at least 1-month. It is waterproof to 1500 m (~5,000 ft) for 2 weeks. The Underwater Piezo Electric Accelerometer is waterproof to at least 300 m (~1,000 ft.) for at least 1-month. It is also waterproof to 1500 m (~5,000 ft.) for 2 weeks. The Underwater Main Cable is waterproof to 1500 m (~5,000 ft.) for 2 weeks except for its top end that connects directly to the PDA-8G.

For the Shallow water Sensor System, the Strain Transducer, Piezo Electric Transducer, and Piezoresistive Accelerometer (Model K) are waterproof to 50 m for 2 weeks.