Sentinel V Plays a Role in Improving the Quality of Marine Food

Researchers from Fiskaaling P/F Analyze the Impact of Offshore Currents and Waves on Our Marine Food Supply

OVERVIEW
The field of aquaculture is becoming increasingly important as the global demand for marine food rises. Fish farming is conducted primarily in relatively sheltered, still waters; however, as the industry grows, farms are being forced to expand into locations that are exposed to currents and waves. This impacts cage design and harms the welfare of the fish, and thus impacts the quality of marine food. In order to ensure a more sustainable production of quality marine food in exposed current and wave-heavy waters, the aquaculture community needs more knowledge about the interaction between the physical environment, current cage design, and caged fish behavior. The use of the five-beam Sentinel V Acoustic Doppler Current Profiler (ADCP) will help to correlate video recordings of fish behavior with exact offshore current and wave activity impacting the cages.

Location: Miðvágur, Faroe Islands

SOLUTION
Earlier this year, an important study was conducted off the coast of Miðvágur, a village in the Faroe Islands, which analyzed the impact of offshore waves and currents on cage deformation and caged fish behavior. Led by Knud Simonsen, Ph.D., of Faroe Islands-based research organization Fiskaaling P/F, researchers instrumented a commercial sea cage to monitor the reaction of caged salmon to variations in the current strength and sea state. To analyze the current and wave activity at the site, the team used a five-beam Sentinel V ADCP. The raw velocity data from the Sentinel V’s five beams allowed for the accurate estimation of wave kinematics that leads to cage deformation.

RESULTS
The Sentinel V ADCP was deployed in a bottom frame at about 35m depth, and at a sufficient distance from the fish farm in order for measurements to be unaffected by sheltering of the farm. Typically, there are 10-12 cages in a commercial salmon farm in the Faroe Islands. One of the cages was instrumented with four cameras to monitor the fish behavior and the movements of the net pen. These observations consisted of one-day periods several times during the duration of the deployment. Also, nine pressure sensors were mounted at different depths on the net pen for continuous monitoring of the vertical movements of the cage structure. The behavior of the salmon, as observed from the cages, will be sought to be classified into typical swimming patterns both horizontally and in the vertical, which will be related to the recorded current profiles and wave data.

The system was deployed from December 20th, 2014, through January 13th, 2015. On January 7th at 7:30 A.M., the largest waves of the deployment were measured, possessing a significant wave height of 3.8 meters with a maximum wave height of 5.2 meters.

The maximum currents in the record occurred during the evening on December 25th, 2014 just before and after the high tide. As can be seen in Figure 2, at 7:40 PM, just before high tide, the currents were flooding with a depth averaged speed of 0.38 m/s at 357 degrees. The highest velocity in the water column of 0.42 m/sec was actually near the bottom at a range of 7 meters from the ADCP.

At 11:40 PM, as seen in Figure 3, just after the high tide, the currents were ebbing with a depth averaged speed of 0.28 m/s at 235 degrees. The highest velocity in the water column of 0.286 m/sec was near the surface at a range of 25 meters from the ADCP.

Figure 4 is a three-minute duration time series of the echo intensity from the Sentinel V’s vertical fifth beam during a period with large waves. The range to the surface derived by identifying the range with the highest echo intensity (red). The regions of moderate return (green/yellow) indicate the presence of bubbles at the surface from the white capping waves. At 7:24:30 A.M., a large wave group passed the ADCP with a maximum peak to trough height of 3 meters.

Figure 1: Sentinel V data from Teledyne RDI’s velocity software.

Figure 2: Sentinel V data from Teledyne RDI’s velocity software showing water column velocity before the high tide

Figure 3: Sentinel V data from Teledyne RDI’s velocity software showing water column velocity after the high tide

Figure 4: Sentinel V data from Teledyne RDI’s velocity software showing the echo intensity from the vertical beam

A total of 29 individual oscillations are easily recognizable during the three-minute time series. The maximum vertical velocities of >1.5 m/sec up (red) and down (purple) January 7th from 7:24:20 A.M.

Specifically, data from the Sentinel V’s vertical fifth beam will be used to correlate video images of fish behavior and net geometry changes. Additionally, the comparison of the vertical velocity recorded by the ADCP’s vertical beam and the vertical/error velocity from the Janus beams will provide the team with the quality assurance needed to calibrate the numerical models of net distortion under waves.

Figure 5: Sentinel V data from Teledyne RDI’s velocity software showing corresponding vertical velocities due to the passage of waves

SUMMARY
The Sentinel V’s versatile five-beam configuration and its ability to measure vertical velocity provided critical study data to the Fiskaaling P/F research team.

The raw velocity data from the Sentinel V’s five beams allowed for the accurate estimation of wave kinematics that deform cages during maximum wave surges. Now, the team will continue to work on correlating the current and wave data with the observed caged fish behavior and cage deformation. With this information, researchers and commercial interests can work to create innovative cage designs that will efficiently withstand offshore currents and waves, improve the welfare of caged fish in these locations, and ultimately improve the quality of marine food globally.

View the Teledyne Marine case study