The final "tow"- end of five years of surveying along the West Coast

By Grant van der Heever, Charles von der Meden and Lara Atkinson, SAEON Egagasini Node Tweet

Figure 1. Dead skate in a benthic trawl lane Figure 2. The first observation of a slime head fish (Hoplostethus sp.) in this area Figure 3. A downward-facing drop camera attachment was mounted to the underside of the SkiMonkey camera frame to obtain close-up imagery of the species on the seabed Figure 4. The "Monkey's Eye"

Monday 22 January 2018 marked the fifth and final embarkation on board the Department of Agriculture, Forestry and Fisheries' (DAFF) research vessel, Ellen Khuzwayo, for the last Benthic Trawl Experiment Cruise for this phase.

Equipped with the SkiMonkey III benthic camera, grabs, a dredge and four years of prior experience (BTE 2014-2017), the scientific crew were confident and ready to take on the eight-day scientific voyage far up the West Coast.

This final survey brings to an end the current project, which set out to track changes in marine life on the seabed following the experimental closure of a small area of the West Coast trawl grounds. Since trawl fishing ceased in three demarcated lanes within the experimental area in 2014, the multi-institutional group of scientists have annually monitored the invertebrate and fish populations.

As always, Professor Colin Attwood led the scientific team, which consisted of Dr Charles von der Meden (SAEON), Karen Tunley (University of Cape Town - UCT), Grant van der Heever (SAEON), Luther Adams (South African National Biodiversity Institute - SANBI), Fred Fourie (Sea Technology Services) and Patrick Foley (DAFF).

Data collected

As planned, 15 benthic stations were sampled using the SkiMonkey III and a total of 45 grabs were conducted, three at each station. Although no detailed report can be given yet, a number of interesting discoveries can be mentioned.

These include the presence of a dead skate in a benthic trawl lane (Figure 1), the first observation of a slime head fish (Hoplostethus sp.) in this area (Figure 2), and the noticeable absence of bristle worms from areas where they were previously abundant. Further detailed, quantitative analyses are underway to assess whether anecdotal observations are significant.

Novel additions to the SkiMonkey frame

The SAEON Egagasini team are continuously improving the scientific gear used to maximise and diversify data collection during access to the remote study areas. This year, a downward-facing drop camera attachment was mounted to the underside of the SkiMonkey camera frame (Figure 3) as an attempt to obtain close-up imagery of the seabed and species thereon.

The camera team also carried out an impromptu removal of the starboard flash and the insertion of a GoPro into the flash housing unit (Figure 4). This improvised set-up was later termed the "Monkey's Eye".

Both the addition of the drop camera mounting and impromptu "Monkey's Eye" modification were successful, with the drop camera mounting providing a closer look at the seafloor and the "Monkey's Eye" providing the system with a wider field of view and a video across the entire transect. Due to their success, the drop camera mounting and "Monkey's Eye" will be added as permanent modification to the SkiMonkey camera system.

Over the course of the next 12 months, the scientists will be engaged in processing the samples, analysing the data and preparing a final report about the findings from the five-year Benthic Trawl Experiment.