Tags and Telemetry
To track the movement patterns of medium to large marine animals, marine biologists often capture them, put tags on them, then release them back into the wild. The tags can be simple pieces of engraved metal or plastic that rely on the general public (fishermen, beachcombers) to find and report when found. Or they might be highly sophisticated devices that send signals at regular intervals, either to listening devices at fixed locations, or to satellites. They might be attached on the outside of the animal or injected into the body.
CTDs with Niskin Bottles
The CTD (conductivity-temperature-depth) is a device used throughout oceanography to collect basic data about the local water column. A Niskin bottle is a heavy-duty plastic bottle open at both ends, with lids that snap shut on command - useful for taking a water sample at a specific depth. Water samples are an important part of any marine biology research involving microplankton or nutrients. On most research vessels, the CTD and several Niskin bottles are part of an overall package called a CTD rosette.
SCUBA divers can photograph, videotape, record sound and run experiments in relatively shallow underwater environments like coral reefs, or close to the surface in the open ocean. Contrary to popular belief, scuba diving is not a big part of every marine biology research project. In general, scuba divers are somewhat like astronauts are to astronomy - extremely expensive techs for deploying, maintaining and retrieving large, complex machinery left underwater for long periods of time (that can photograph, videotape, record sound and collect other oceanographic data).
Remotely operated vehicles (ROVs) are used in marine environments deeper than is safe for divers. These are attached to the boat - and the researcher on board - with a cable that can transmit commands and often receive data in realtime.