Deployment Days & Methodology Used

The morning began with a meeting at the university at 8.30 am. The bait had been collected fresh from a supermarket that morning and the equipment loaded into the van (including the crane, its cables and battery) and transported to the research vessel docked at the port. Particular care was given to not move the camera housings and the BRUVS setup was positioned in the van in a way that minimized as much as possible any impacts to the housings. On the boat journey out to the first sampling location, the bait box was secured by use of a screwdriver, with larger holes near the base of the bait box allowing access to the pipe clamps within. Zip ties were added to the bait pole to ensure its fixation and the bait was cut up/crushed into smaller pieces with the help of box cutters and gloves.

Having arrived at the randomly chosen sampling location, the bait (squid for the pilot deployment) was then transferred into the bait box, a splash of fish oil added and the box closed by use of zip ties.

Cameras were checked again to ensure full battery and memory storage and then transferred into their housings on the BRUVS. Finally, with all crew members ready, the cameras were turned on at the same time, checked to see they had begun filming and the BRUVS was transported to the edge of the vessel by two people, whilst an additional person handled the bait box and the bucket placed below it to avoid bait spilling onto the boat deck.

Relevant information displayed on the boat’s monitors was noted down in a field notebook as soon as the BRUVS was gently placed in the water and already making its way to the seabed. This included the depth, the GPS coordinates of the sampling location, the start time of the deployment (time in) and water temperature.

An alarm was then set to indicate the time of retrieval and the crane was used to facilitate bringing it back onto the boat. The stop filming button was pressed on the GoPros once the BRUVS was set back on the boat and the cameras were removed from their housings. The videos were then transferred onto a laptop immediately after the retrieval process and the time of retrieval (time out) noted.

Deployment Day 2

On the 7^th of May 2021, the second day of deployment was conducted which followed the same procedures outlined for the pilot deployment. Bait from the last deployment was still usable so it had been frozen and stored in the university cold room and defrosted on the trip to the first sampling location. This was done by placing the bait bags in a bucket filled with water at the port. Three deployments were conducted that day and the visibility was much better than the pilot deployment. No fish were observed; however, a crab was attracted to the bait box during the third deployment.

Deployment Day 3

Sardines were used this time instead of squid and defrosted overnight from home. Four deployments were conducted, with shorter times between deployments than previously as four microSD cards were used. This allowed the BRUVS to be deployed more rapidly as the footage could be transferred while the next deployment was already underway.

An external hard drive disk had also been ordered and used since it was noticed that the compounding of the videos required very large storage space.

Unfortunately, there were rough sea conditions for several days prior to the deployment day which strongly affected visibility and no marine fauna could be seen with the BRUVS footage (including the bait box not being visible for the first deployment of the day).

Deployment Day 4

On the 3^rd of June, the visibility was superior to the previous sampling trip, albeit with fast underwater currents noticeable with sediment particles shooting past the cameras. The deployments were chosen to coincide with the optimal tidal period. A surplus of bait from the previous trip was used, with the defrosted sardines easy to crush by hand. Although the sea conditions were better, no marine fauna could be observed with the cameras.

Deployment Day 5

Fresh anchovies bought the previous day were used as bait for the last deployment trip of the professional practice that took place on the 4^th of June.

This was the most successful data collection day, with several marine fauna taxa being recorded by the video surveys. Schools of Boops boops fish and wandering crabs were observed during both the first and second of the four deployments conducted.

In addition, a fish of the genus Trachinus approached the BRUVS along the sandy bottom during the third deployment, following which the visibility deteriorated for the final deployment when the winds picked up and the waves increased in height causing additional turbidity.