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Visuals from the deep
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By Lara Atkinson and Charles von der Meden, SAEON Egagasini Node
Descending into the darkness - it is pitch black beyond the camera lights and nobody knows what may suddenly appear on the screen before us.
The excitement and anticipation is tangible in the tiny operations room aboard the R/V Ellen Khuzwayo (Department of Agriculture Forestry and Fisheries research vessel) where researchers from SAEON (Dr Charles von der Meden) and the University of Cape Town (A/Prof. Colin Attwood, Karen Tunley and Stuart Norman) are huddled, staring at a screen.
A flash of silver fish appears on the screen and then vanishes again. Colin leaps out his seat and shouts "Did you get that one Charles?"... but alas, it darted past too fast and escaped being captured by the click of the camera. Everyone settles down, staring at the screen again … and this is mostly how we passed our days from 2 to 9 February this year on board the R/V Ellen Khuzwayo, when the first South African trawl closure benthic experiment got underway.
Assessing the effects of trawling
The impacts of demersal trawling have been cited as one of the largest global anthropogenic sources of disturbance to the seabed and its biota (Jennings and Kaiser, 1998). Several international initiatives are striving towards gaining a better understanding of these ecosystem impacts, specifically in different habitats subjected to different types of fishing pressure.
Although the demersal trawl fishery in South Africa is considered to be well managed, very little is known about the effects of trawling on the biodiversity of deepwater habitats and biota and this remains a high research priority. As part of their commitment to retaining Marine Stewardship Certification (MSC) for the South African hake fishery, the South African Deep-Sea Trawl Industry Association (SADSTIA) are collaborating with researchers from SAEON, the University of Cape Town (UCT) and the South African National Biodiversity Institute (SANBI) in an experiment that aims to assess potential recovery of the seabed after more than 100 years of trawling.
The trawl industry have agreed to stop trawl fishing in portions of an area offshore on the West coast of South Africa while continuing trawling in demarcated lanes for a period of at least four years (Fig. 1). The experimental area lies 108 nm west of Groenriver mouth at depths between 360 and 510 m adjacent to a submarine mound called Childs Bank.
Baseline survey
After several years of planning, the first baseline survey and samples were collected in February 2014 using SAEON’s deep-sea SkiMonkey III camera system and benthic grabs deployed from the Ellen Khuzwayo. Using the SkiMonkey III, researchers successfully captured three hours of video footage and 1 928 still images of the seabed at 15 stations in the experimental area.
The footage and stills will be analysed for epifaunal community composition and abundance. Benthic grab samples collected at the same 15 stations will be analysed for infauna and sediment properties. It is anticipated that over time (at least four years), the benthic fauna (both epifauna and infauna) are likely to change in the lanes that will no longer be subjected to the disturbance of trawl fishing. Annual sampling in areas closed and open to trawling will allow any changes in colonising communities to be detected.
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Quantifying epifauna
Dr Lara Atkinson of SAEON’s Egagasini Node is identifying and quantifying the epifauna seen in the visual footage from the seabed in the experimental area. In order to do this as accurately as possible, she will be cross referencing the species seen in the footage with those already identified from research trawls in the same area over the past few years.
Lara has been steadily building taxonomic knowledge of offshore trawl invertebrate species through the Offshore Trawl Invertebrate Identification Guide that she and a team of researchers have been developing since 2011. The identification guide will be very useful in accurately identifying the epifauna seen in the footage.
A first for South Africa
This experiment is the first time researchers will have the opportunity to conduct quantitative measures on benthic fauna in a South African deep offshore habitat. There will be several challenges with some of the identification work as specimens seen alive in their natural habitat with the camera, may look completely different to those rather mangled specimens that are landed on the trawl deck.
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As one example of the challenge that lies ahead for Lara, below is an example of a beautiful deepsea anemone living in the seabed in the experiment area as captured with the camera, followed by photos of the two most likely anemones that this specimen could be from the identification guide. The specimens photographed for the identification guide were obtained from a research trawl net and linking these species to those seen in the footage is likely to require careful attention to detail, advice from taxonomists, some imagination and a lot of time.
All participants in this experiment are very excited about the research, which is certainly the first of its kind in southern Africa and the first such industry-science collaborative research to be conducted at such depths in soft sediment habitat in the world. Watch this space ...
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Acknowledgements
We would like to gratefully acknowledge the Department of Agriculture, Forestry and Fisheries (DAFF) for making the research vessel Ellen Khuzwayo available to implement this research - a collaborative effort among SAEON, UCT, SANBI and the South African Deepsea Trawl Industry Association.
Reference
- Jennings, S. and Kaiser, M.J. 1998. The effects of fishing on Marine Ecosystems. London: Academic Press. pp. 203-314
