Gallery 2.3: Vessel Monitoring System

All purse seine vessels fishing for tuna are required to use a Vessel Monitoring System (VMS) as directed by the RFMO in which they are operating. These units, at a minimum, transmit a vessel’s position at regular intervals to a central agency. This vessel surveillance can be used to identify illegal fishing in closed areas or during closed periods. It is important that the VMS units are operational and transmitting at all times during the trip. Observers should note the unit’s make, model, and operability. If the unit has tamper-proof seals, ensure that they are intact.

The size and construction characteristics of the purse seine net influence the catch of both tuna and nontarget species. Recording an estimation of the net size and depth will allow RFMO scientists to track the relationship between net characteristics and catch. In general, the net measures 1,500 to 2,000 m long and 120 to 250 m deep. The size of the mesh in the main part of the net is usually around 120 mm when stretched. The top of the net is mounted on a floatline and the bottom on a leadline. The leadline generally consists of a steel chain with steel rings, known as "purse rings," attached below the chain. The purse line, which runs through the purse rings, is made of steel and allows the pursing of the net. The deckboss, navigator, or chief engineer may have access to the vessel’s net diagram, and this will help you record accurate specifications of the net. Presence of any size-sorting net component or any other experimental gear designed to modify the size of the catch and bycatch should also be described and recorded for future reference.

Vessel Monitoring Systems (VMS) transmit the location of a vessel to a central recording site on a regular basis. (Photo: SPC)

The VMS has two components onboard: the transceiver box (two examples on right) and the antenna (left). (Photo: SPC)

The organization that administers the VMS program will often seal the transceiver box with special stickers to prevent tampering with the unit. (Photo: SPC)

It is important to note any evidence of tampering with the VMS unit. (Photo: Joshua Sione, JCS)