An acoustic detection system developed by Canadian company Notus to enable shrimp trawler skippers to identify where their catches are being caught has been adapted to provide the same advantages for prawn trawlers.
The Echo detects the sound of shrimp hitting the bars of a shrimp trawl’s selection grid, and this is relayed to the trawler’s wheelhouse where the information is shown on a display. Since its release around a year ago, the system has been adopted by US and Canadian shrimpers.
‘The west coast of the US is a big market for us and in Canada the majority of the top producers use this,’ said Francis Parrott at Notus.
‘With the shrimp trawlers we found that in a three hour tow, the catch might only be taken in 40-50 minutes. So this shows where the sweet spot in each tow is. It has really opened people’s eyes to exactly where they are catching.’
Now the same technology has been adapted for the prawn (nephrops, langoustine) fishery, which presents many of the same problems for skippers – that the target species have no swim bladder and therefore don’t show up on an echo sounder. But the acoustic detection tells the skipper exactly where in each tow the catch is being caught.
‘We have been doing some very promising work on this in Denmark. Even with very low catch rates, it still detects prawns,’ he said, adding that the sensitivity can be increased by a technician for to maintain effective detection when catch rates are low.
‘What has been a problem is that the prawn trawlers don’t use grids, so we have developed a pickup device,’ he said.
This is a low-standing set of bars that is placed in the tunnel of the trawl as a sounding board. Prawns passing through the gear hit the pickup’s bars before passing through and back to the codend, but the contact generates an acoustic marker that is relayed to the wheelhouse, where the data is displayed.
The data is shown as a figure, but more importantly as a graph that shows at which point in the tow the sound level was most dense.
‘There’s a learning curve to reading the graph. You get used to interpreting the data, and looking for the lines that indicate steady fishing, while the spikes that also show on the readout tend to be fish rather than prawns hitting the pickup device.’
‘The interest at this show has been tremendous,’ he said, speaking at the Skipper Expo in Aberdeen, where the Notus stand had been busy practically from the moment the doors opened.
‘It has really opened people’s eyes to what is possible and you’re going to see a lot of these in Scotland.’
The Echo system is run via a battery-powered sensor on the grid or pickup device. This takes an hour to recharge and will run for around three days on a single charge.
Notus is represented in the UK by TecMarine in the South-West and by Seafield Navigation in Scotland.