There is no one best practice to minimise the impacts trawling has on ocean habitats, according to leading fisheries scientists and managers.

The top fisheries experts from around the world joined forces to create a new study in the effects of trawling on the marine environment. The study was mainly carried out in the water around Alaska, which hosts a wide variety of fish stocks.

The report found that bottom trawlers land around 19 million tons of fish and invertebrates annually, almost one-quarter of wild marine landings. The extent of bottom trawling footprint (seabed area trawled at least once in a specified region and time period) has often been contested but poorly described.

In their studies, the researchers found that some ocean bottom habitats are more sensitive to trawling than others. It was found that habitats that are subject to a lot of natural disturbance are less sensitive to disturbance by trawling. Similarly, what works in one place might not work elsewhere, for example Alaska has some of the healthiest, best managed fish stocks in the world. But what works in Alaska will not work everywhere.

“The key to best practices is local context,” said Bob McConnaughey, the NOAA Fisheries Alaska Fisheries Science Center biologist who led the study. “Fisheries managers everywhere have common goals. They need to ensure that ecosystems and fish stocks remain healthy to support fishery benefits over the long term. But they operate in different environments with different priorities, resources, and societal values.” 

The team reviewed management measures and voluntary industry actions currently used to reduce trawling impacts in artisanal to industrial trawl fisheries around the globe. Such measures include absolute prohibition of bottom trawling, gear modifications, area closures, bycatch quotas, and limits on trawling effort.

Determining the balance between biological, ecological and socio-economic objectives is a major challenge in fishery management. To remain sustainable and promote ecosystem-based fishery management, fishing must minimize damage to the ecosystem that supports fish stocks. But protecting habitat can limit the immediate employment, income, and food security benefits of fishing.

“Alaska has a number of healthy fish stocks in part due to good science and management and a strong relationship with the fishing industry.This means that fishermen are able to catch their quota in relatively small areas. That leaves vast areas in a nearly pristine state and available for habitat conservation measures,” says McConnaughey. “In contrast, management capacity is still developing in Vietnam, which has open-access trawl fisheries. There is limited habitat protection. For instance, nursery areas are not protected because juvenile fish are marketable. The opportunities to manage trawling impacts on the seabed are thus very different.”

Bottom trawling accounts for about one quarter of global marine fisheries landings. Designed to capture fish and shellfish that live on or near the seafloor, trawling activity can disturb bottom habitat. This has the potential to temporarily or permanently alter seafloor habitat. Consequences can cascade through the ecosystem. Seafloor disturbance may:

  • Change the physical characteristics of the habitat.
  • Modify chemical processes.
  • Reduce abundance, biomass, diversity, body size, and productivity of life on the ocean bottom.

These changes in turn can affect the commercially important fish, and fishing communities, that are supported by the ecosystem. 

Some ocean bottom habitats are more sensitive to trawling than others. Habitats that are subject to a lot of natural disturbance are less sensitive to disturbance by trawling. The seafloor of Alaska’s Bering Sea is relatively resilient to trawling activity, because of regular exposure to natural disturbances such as intense storm waves and strong currents. Naturally stable ocean habitats, such as coral reefs and deep areas, are more vulnerable to disturbances.  

In fisheries that are managed sustainably, trawling effects are minimised because the area trawled—the trawling footprint—is small. As the health of stocks improves, the same or a larger quantity of fish can be taken in smaller areas. Some geographic regions trawl less than 1 percent of their fishing grounds; others more than 80%.  

In Alaska’s Bering Sea, only about 8 percent of the bottom is trawled each year. In some countries trawling is much more widespread and there may be large numbers of people fishing depleted stocks. Although highly desirable, there may not be the technology or resources or data to effectively monitor and manage trawling impacts. 

Alaska is fortunate to be in a position to fish conservatively. But not all regions of the world are.

“Ultimately, if you minimize the environmental impacts, you may satisfy the social and economic needs. But can a fisherman wait if he or she needs to feed his family today?” says McConnaughey.

“We need to recognize different circumstances, to take into account economy and culture as well as ecosystem,” McConnaughey says. “The Trawling Best Practices Project is developing assessment tools and management guidelines that are applicable to the full spectrum of local circumstances.”

Source: NOAA

Bottom Trawling Impacts depends on Local Marine Environment

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