Benthic communities can take more than 6 years to recover from a single pass by a hydraulic dredger, according to the results of a new international study into the impacts of various trawl systems.
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An international collaboration of scientists conducted a global meta-analysis of 70 comparative and experimental studies on the effects of bottom trawling, to estimate the rates of depletion and recovery of seabed biota following bottom trawling.
The researchers were able to quantify the relationship between the reduction of seabed animals and penetration of the fishing equipment into the seabed.
Lead author Professor Jan Hiddink from Bangor University, said: “We found that otter trawls penetrated the seabed 2.4 cm on average and caused the least amount of depletion of marine organisms, removing 6% of biota per trawl pass on the seabed.
“In contrast, we found that hydraulic dredges penetrated the seabed 16.1 cm on average and caused the greatest depletion, removing 41% of the biota per fishing pass.”
Depending on the type of fishing gear, penetration depth, and environmental variables such as water depth and sediment composition, recovery times for seabed biota ranged between 1.9 and 6.4 years.
Trawling contributes 20% of the global landings of fish caught at sea, hence it is an essential means of providing food for millions of people.
Bottom trawling is used to catch fish and shellfish that live in or near the seabed.
Despite its importance, it causes variable amounts of physical and biological change to seabed habitats, and can induce structural and functional changes in seabed communities.
Understanding the ecosystem consequences of trawling is important so that we can reduce negative impacts on the seabed through appropriate management measures.
Professor Ray Hilborn of the University of Washington, Seattle who led the collaboration with Professors Michel Kaiser (Bangor) and Simon Jennings (International Council for the Exploration of the Seas, Denmark), said: “These findings fill an essential science gap that will inform policy and management strategies for sustainable fishing practices by enabling us to evaluate the trade-off between fish production for food and the environmental cost of different harvesting techniques." ■