A method and apparatus to implement a trolling device. The trolling device can assist maritime sports fishermen in defining the actual water depth and/or water temperature of the location at which a lure is situated in troll. The readings from the device enable an angler to adjust variables such as boat speed, length of line deployed and ballast weight to adjust to desired depth. The device comprises a temperature sensor, a pressure sensor, a micro-controller chip, a printed circuit board, an LCD display, and a cycle switch, all housed within a dense metal (for ballast), water-proof body designed specifically for deep marine submersion and in-line trolling. The device has a pre-programmed data-logging algorithm that is activated by a fisherman via a magnetic controlled reed switch prior to letting out trolling line with the device set in-line to the trolling gear. Upon retrieving the device, the fisherman can view the data to place or reset the trolling lures/rigs, as necessary, at the appropriate zone.