Scallop dredges attached
together on a beam at a fishing dock in the Netherlands. Photo courtesy of
Jeremy Collie.
About a third of the world’s fish is caught using bottom
trawling, a method that drags a net along the seabed, scooping up everything in
its path.
The ecological damage can be devastating. Many marine
creatures—sea turtles, corals and anemones—are accidentally caught, and often
die. As it scours the bottom, the trawl can also destroy marine habitats
crucial to a thriving ecosystem.
But some trawling techniques are more damaging than others.
That’s the conclusion of a study by University of Rhode Island
Oceanographer Jeremy Collie and a group of international scientists.
Collie and other researchers studied four different trawling
techniques and concluded that otter trawling, a method that uses two doors to
hold the net open, is the least harmful to marine organisms.
Collie says that the study should be of great interest to
New England fisheries, which have used trawling to catch fish for decades and
are often embroiled in debates with marine conservationists about whether to
ban trawling, or limit the practice.
“Bottom trawling causes physical and biological change to
seabed habitats and can cause structural and functional changes in seabed
communities,” the scientists concluded.
“Understanding the ecosystem consequences of trawling is
important so we can reduce negative impacts on the seabed through appropriate
management measures.”
The team looked at 70 previous studies on the effects of
bottom trawling to determine which methods were most harmful. The studies
focused on waters off the East Coast of the United States and Western Europe.
Besides otter trawling, the group also studied beam
trawling, a method that uses a metal beam to hold the net open. The team also
looked at towed dredges that drag a toothed metal bar along the seafloor and
hydraulic dredges, in which a jet of water loosens the seabed to capture
creatures living in the sediment.
Otter trawls removed 6 percent of marine organisms each time
the net passed, according to the study. Hydraulic dredges caused the most
damage, removing 41 percent of animal and plant life on the seabed, the study
reports.
Depending on the type of fishing gear, penetration depth and
environmental factors such as water depth and sediment composition, recovery
for marine organisms ranged between 1.9 and 6.4 years.
“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,” says Ray Hilborn, a
fisheries professor at the University of Washington, Seattle, and another study
co-author.
The findings are part of the Trawling Best Practices
Project, which is looking at the impact of trawling worldwide and hopes to
publish trawling guidelines for the fishing industry that focus on preserving
the marine ecosystem.
Collie expects to remain involved in the project for years
to come.
“In addition to calculating the mortality of marine animals
caused by bottom trawling, this study provides some of the first estimates of
their rates of recovery,” he says. “Combined with high-resolution maps of
trawling efforts, this work allows us to estimate the impact of bottom trawling
on seafloor communities worldwide.”
Collie collaborated with a prestigious group of scientists
from various institutions including Bangor University in the United Kingdom,
the Commonwealth Scientific and Industrial Research Organization in Australia,
the Institute for Marine Resources and Ecosystem Studies in the Netherlands,
the Alaska Fisheries Science Center in Seattle, Centro Nacional Patagonico in
Argentina, and the United Nations Food and Agriculture Organization in Rome.
The project was funded by the David and Lucile Packard
Foundation; the Walton Family Foundation; the Alaska Seafood Cooperative;
American Seafoods Group; Blumar Seafoods Denmark; Clearwater Seafoods; Espersen
Group; Glacier Fish Company; Gortons; Independent Fisheries New Zealand; Nippon
Suisan, United States; Pacific Andes International Holdings; Pesca Chile, South
Africa; San Arawa, South Africa; Sanford New Zealand; Sealord Group, New
Zealand; South African Trawling Association; and Trident Seafoods.
Government funding was provided by the United Kingdom
Department of Environment, Food and Rural Affairs; the European Union Project;
the International Council for the Exploration of the Sea Science Fund; and the
Food and Agriculture Organization of the United Nations.