from: http://www.nature.com/nature/journal/v387/n6634/pdf/387665a0.pdf

Most of the article is about their results, but it does list some (basic) information about their process that is interesting:

• Records depth (0-100 meters)
• Records water temperature (-4 to 23 C)
• Two Types: MK1 and MK3
  • Mk 1 stores 32000 data points and weighs 55g (flatfish only)
  • Mk 3 stores 500000 data points and weighs 16g (flat and round fish)
    • Also stores information on light intensity

The tags are attached to fish during research trawls. The tags record the data as the fish swim around, and then the tags are returned to the scientists when the fish are caught by fishermen. Their data indicates that the tags do not impact the fishs' mobility.