Connect transducer to an Arduino Uno with GPS Shield

My transducer is an airmar dst800 and the data wiring says "nmea +" and "nmea -". I'm not sure now how to really connect this sensor to my Uno. Are "nmea +" equal to tx for example?
I use SoftwareSerial to communicate with the Gps-shield and I guess that I can use this library to communicate with the transducer aswell?

Best regards
Robert