Buoys getting smarter

Based in France’s tuna capital of Concarneau, ISI-Fish represents Spanish company Marine Instruments, supplying a range of floating buoys for tropical tuna fisheries.

“We supply buoys for longliners, but as these don’t go far from their lines. These work with our MSB Palangre software for surface lines or MSB Casea for demersal longlining.

“There’s no need for satellite technology and so these use radio signals for tracking, which is a more cost-effective option with no communication costs.” explained Gildas Bodilis, commenting that the purse seiners require a more sophisticated set of options to cover a wider area and also to gather a great deal more data.

“These are floating buoys that are use to track fish aggregation devices (FADs) so they know where the FADs are and what is under them.”

The more basic M3i buoy contains a 50kHz sounder that relays soundings taken at five minute intervals back to the catching vessel, although with real-time processing taking place within the buoy itself, costs are kept down with the optimal results transmitted via an Iridium satellite link, along with the buoy’s position, sea temperature and the battery level.

The buoys have a virtually unlimited battery life, as solar panels ensure that the batteries are kept topped up.

The more sophisticated M4i buoys are built with a tri-frequency sounder operating at 50, 120 and 200kHz.

“There are different echoes from different species, as they don’t have swim bladders that reflect signals in the same way. 200kHz is best for focusing on skipjack, while yellowfin and bigeye tuna show up best at 50kHz,” he said, adding that a more recent addition to the range is the M3iPlus buoy, with two frequencies.

“These ping every minute at 50kHz and 200kHz, as well found that these were the two most effective frequencies to use.

“This buoy also has an inclinometer so there isn’t a sounding if it’s rolling too much for it to get a good image.

“It also has day and night modes, as well as having a sunset mode to be able to concentrate particularly on the crucial 30 minutes before and after sunset when the tuna are most heavily congregated.”

In addition, there is the option to poll buoys for an instant sounding snapshot and position.

The buoys are made to be relatively simple, while the sophisticated software is on board the catching vessel, and this includes a number of features that are about to be included early next year, such as being able to tell more precisely if an echo is fish below the FAD or a thermocline and to sense temperatures at different depths, as well as overlaid against sea currents, chlorophyll levels and wind strength at the surface.

The buoys are compatible with MaxSea, OrbMap and CatSat systems, allowing a picture of sea conditions over a wide area to be built up and displayed in a purse seiner’s wheelhouse.

Due to the solar panels fitted to the floating buoys, they have unlimited battery life.

“We also produce a scientific buoy, which has seven transducers that leave nowhere to hide. These are used by scientific institutes looking to understand the distribution and size of tuna and there are a lot of floating devices used for scientific purposes to track stock levels, as there is still a lot that we don’t know about tuna,” Gildas Bodilis said.