Mobile fish size and species analysis tool

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Mohn Technology has over many years worked with a combination of computer vision software combined with underwater technology.

During work with mackerel fishermen and marine biologists who specialise in pelagic fisheries we discovered a need for better technology. The fishermen got too little information from their sonar, and wanted to know more about both fish size and species in the school they have found. This is both because of the economy, as the price they get for pelagic fish like herring and mackerel is size dependent, and due to their quota is a specific species.

 

As a proof of concept Mohn Technology developed and manufactured a towfish with 100m depth rating, named Mohn Technology Fishbot Towfish. It includes the following components and sensors:

  • Onboard computer with real time AI detection capabilities (Edge computing)
  • Battery
  • Two x 1000 lumen lights
  • Single beam sonar
  • Two stereo cameras (directed laterally to each of the sides)
  • Two wide angle machine vision cameras (directed laterally to each of the sides)
  • Pressure (depth) and temperature sensor
  • 60m umbilical with the ability for real time data transfer (streaming), 100m depth rating
  • Battery powered top side box containing communications board and router with Wifi Interface. Allows connection through both PC and Mobile.

Specs:

  • Weight in water: ca 3.5 kg (35N)
  • Weight in air: ca 15 kg (150N)
  • Dimensions:
    • Length 1m
    • Body diameter: 0.18m
    • Maximum fin width (diameter): 0.34m
  • Umbilical force when towing (apx):
    • 0 knots – 3.5 kgf / 35 N (Just the submersed weight pull on the umbilical)
    • 2 knots – 3.7 kgf / 37 N
    • 3 knots – 4.8 kgf / 48 N
    • 4 knots – 6.0 kgf / 60 N
    • 5 knots – 7.1 kgf / 71 N
    • Note that during fast towing the depth is reduced due to the low weight. A depressor fin or extra weight could be added.
  • Operational time (apx):
    • No lights: 10 hours
    • 1 lights: 6.5 hours
    • 2 lights: 4.5 hours

The unit can both be run as a towfish with a 100m cable, where the user gets real time data from the onboard cameras and sensors, OR it can be used as an autonomous recording unit.

For each frame, the video can be paused an measurements can be taken. This will be automated in the future. Example video below taken on the IMR expedition:

When used as a towfish the unit is towed behind a vessel. Both a manned or unmanned vessel is possible due to the very low drag and weight of the towfish.

When used autonomously, the user activates recordings by a magnetic switch. The lights flash to indicate start of recording, and the unit will record using pre-configured settings until it is switched off.

The system has been rented out to the Norwegian Institute of Marine Research (IMR) on a scientific mackerel expedition. The marine biologists wanted to get size and species samples without actually having to catch the fish. The Fishbot was used in the autonomous configuration. The tail was removed and it was mounted inside a cage which was fixed inside the trawl. The system worked well for the whole duration of the expedition. More information can be found here: https://www.hi.no/hi/nyheter/2024/juli/halvveis-i-makrell-okosystemtoket-med-vendla-og-eros