International study measures the impact of trawling on the seabed

In contrast to commonly held views that bottom trawling transforms large portions of the seabed into an underwater desert, the impacts are highly variable and recovery times for plants and animals disturbed by trawling depend on the type of gear used and a range of environmental variables.

These are some of the findings of an international study published in Proceedings of the National Academy of Sciences in July. The study was conducted by a team of 16 researchers who analysed data from trawl fisheries around the globe in an attempt to quantify the impacts of trawling.

Bottom trawlers catch at least 20% of global marine fish catches and consequently trawling plays an essential role in providing food for millions of people. In South Africa, deep-sea and inshore trawlers catch approximately 150 000 tons of hake and other deep-sea species per year. The catch is supplied fresh, or processed and packaged, to seafood markets at home and abroad. A number of low value species caught by these fisheries − such as horse mackerel, snoek and angelfish − are a valuable source of good quality animal protein, particularly in the Western Cape.

Data gathered from the South African trawl fishery for hake was utilised in the trawling impacts study, said Johann Augustyn, secretary of the South African Deep-Sea Trawling Industry Association, SADSTIA.

“Most of the data used in the study comes from fisheries in the eastern United States and Western Europe, but we are pleased to have been included in the study,” he said.

“Understanding the ecosystem consequences of trawling is important to SADSTIA because it will help us to work with the Department of Agriculture, Forestry and Fisheries to introduce appropriate management measures that will reduce negative impacts on the seabed.”

South African trawlers make use of the “otter trawl” system in which a cone-shaped net is held open by two “otter boards” − more commonly referred to as “trawl doors” − while it is pulled along the seabed by a powerful stern trawler. Hake and other fishes living on or close to the seabed are herded into the net by the disturbance created.

According to the trawling impacts study, out of the four trawl methods analysed, otter trawling causes the least damage to the seabed, removing 6% of plants and animals per drag and penetrating the seabed down to 2.4cm on average, in contrast to hydraulic dredges (used to catch bivalve shellfish like mussels and clams) that penetrate the seabed to 16.1cm and remove 41 percent of plants and animals per drag.

“There’s a common perception that you trawl the bottom and the ecosystem is destroyed,” said Ray Hilborn, Professor at the University of Washington in Seattle, United States and one of four co-authors who designed the analysis.
Hilborn was quoted by the University of Washington.

“This study shows that the most common kind of trawling, otter trawling, does not destroy the marine ecosystem, and places that are trawled once a year really won’t be very different from places that are not trawled at all.”
But, says Hilborn, the widespread use of otter trawls means that the footprint of this trawling method is much greater than other trawl methods.

“While otter trawling has the least impact per trawl pass, it is the most widely used of all the bottom fishing gear types and hence its effects are more widespread than are those of more specialized fishing gears, such as hydraulic dredges,” he said.

The study is one part of a larger effort to catalogue the effects of different types of bottom trawling worldwide. This is known as the Trawling Best Practices Project which Hilborn leads with co-authors Michael Kaiser of Bangor University and Simon Jennings of the International Council for the Exploration of the Seas in Denmark.

Ultimately, the team aims to publish a set of fishing-industry “best practices” for the methods, equipment, density and frequency of bottom trawling.

Meanwhile, in South Africa, SADSTIA has collaborated with the University of Cape Town, the South African National Biodiversity Institute, the South African Environmental Observation Network and the Department of Agriculture, Forestry and Fisheries in a five-year study that is using a submersible camera and a benthic grab to closely examine and compare the state of the seabed in three lanes that have been closed to trawling, and two lanes in between them where trawling is allowed.

The seabed experiment enters its fifth and final year in 2018 when a final batch of photographs and samples will be taken. Data analysis and the publication of results will follow.

Read more about the trawl impacts study:

SADSTIA communications manager wins SANCOR award

SADSTIA communications consultant, Claire Attwood, was among seven South African marine scientists, technicians and science communicators to win recognition at the three-yearly South African Marine Science Symposium that was held in Port Elizabeth in July.

Attwood won one of two Marine and Coastal Communicator awards. These awards are made to individuals or groups of individuals in recognition of their outstanding contributions towards communication of information about the marine and coastal environment to the public via various media at various levels.  The awards serves as acknowledgement of, and a symbol of appreciation for, the dedication, enthusiasm and diligence of the such communicators.

The second recipient of the Marine and Coastal Communicator award was Jone Porter, director of education at uShaka Sea World.
Attwood has worked as communications consultant to SADSTIA since 2016. She also works for a number of other companies and organisations, all of which are active in the field of fisheries or marine environmental management. (See citation below.)

“We are proud of Claire’s achievements and happy to be working with a professional of her calibre,” said SADSTIA secretary, Johann Augustyn. “The deep-sea trawling industry is sustainable and internationally competitive and Claire is helping us to communicate some of our successes through a range of local and international media.”

Others who were honoured by the South African Network of Coastal and Oceanic Research (SANCOR) at SAMS were:

SANCOR Young Researchers Award
Acknowledges a new generation of scientists and encourages research excellence in science in the marine and coastal environment

  • Dr Sarah Fawcett
  • Dr Romina Henriques

Derek Krige Medal
Awarded in recognition of outstanding achievements in the field of technical support to marine science in South Africa
In memory of the late Mr Barrie Rose

Gilchrist Medal
Awarded to distinguished marine scientists. The medal serves as recognition of the recipient’s contributions to marine science, to further stimulate excellence in marine science and to focus on South Africa’s marine and coastal environments

  • Prof Peter Ryan
  • Prof John J. Bolton

Recipient of the
Professional Category
Claire Attwood

In recognition of outstanding contributions towards communication of information about the marine and coastal environment to the public. This award serves as an acknowledgement of, and a symbol of appreciation for, the dedication, enthusiasm and diligence of the persons performing such communication.

As an environmental writer/journalist, editor and communications consultant, Claire writes articles on an array of fisheries, aquaculture and fisheries-related issues and produces reviews, reports and copy for various print outlets and programmes. She is also an avid photographer and consults with organizations on their media strategies, within the fisheries and marine conservation sector. In South Africa science communication and pubic engagement is a very small niche with marine communicators being few and far between. Despite this Claire has managed to leave an indelible mark in the area of science communication and public engagement. She has many years of experience as an observer, writer, editor, photographer and journalist in SA fisheries and environmental organizations here and abroad. She has done work in and for countries like Angola, Namibia, Ghana, Tanzania, Mozambique, Bengal and Mauritius to name a few through the various Large Marine Ecosystem programmes. Her expertise is sought after because she has an in-depth understanding of the marine environment coupled with keen insights into the fishing industry, government departments involved with fisheries and policy, fishing companies and their operations and how best to translate complex marine issues to the greater public. Hence her writing, editing, photographing, and graphic designing skills, as well as the ability to develop effective multi-media strategies are impeccable. Additionally, Claire possesses wonderful inter-personal skills and has an extremely good understanding and approach to the human aspects related to fisheries and conservation. She writes well-researched, balanced, high quality, in-depth, perceptive and sometimes passionate pieces. Claire’s writings have extended beyond fisheries related matters into the realm of marine conservation, education resources, training manuals, aquaculture and her outputs are valued and widely utilised by the South African marine science community. She has covered topical and sometime controversial issues through various platforms. She is an extremely professional, committed and talented journalist and science communicator who has played an important role, mostly in the background, by giving an effective voice to those who need to share their messages and viewpoints, be these heads of government departments, CEOs of companies, fisher folk, scientists or fisheries managers. Her writing has helped government departments, fishing industries and other programmes/organisations develop more friendly and open public profiles which has often resulted in communication channels/collaborations being unlocked. She fully deserves to be recognized for the important role she has played as a marine science communicator and for being a great example of quality and professionalism in this field.