I have a stack og handwritten GPS coordinates - from an observer in the field - and I want to map them in ArcMap and do basic calculations. Length of transects etc. However I am stuck almost at the first step I don't know what coordinate system the lats and longs are in. I would appreciate any help, and tips to recognizing projected coordinates in the future:

An example of the coordinates are:

**39.45-314 E and 148.21-635 S**- Off the coast of Tasmania - I know that much.

Just putting them straight into google maps seems to give the correct locations, but I want to use them in ArcMap and use them to measure distances between points. I initially assumed they were in MinDec and just converted them to decimal degrees for mapping, but I am not sure. Please help a struggling biologist, I know this should be easy once I get the coordinates sorted in my head.