Trawling: Fragile life at the bottom of the sea

This article originally appeared in The Circle: Arctic biodiversity in the spotlight. The Circle shares perspectives from across the Arctic, and the views expressed here are not necessarily those of WWF. See all Circle issues here.

Greenland’s deep seafloor is home to a diverse assembly of benthic fauna, including corals and sponges. Deep-sea fisheries are vital to Greenland’s economy, but trawling can damage benthic species by dragging heavy gear across the seabed. In fact, a team of marine scientists from Nuuk, Greenland and London, England, explored the seabed using underwater cameras and found that these habitats have undergone substantial change due to trawling. As Mona Fuhrmann discusses, these findings challenge the industry to reach conservation goals.

Imagine diving down to 1,000 metres below the sea surface of West Greenland. You would find complete darkness, icy temperatures and pressures that no human would survive.

Yet the sea floor is home to a peculiar community of organisms that have adapted to this harsh environment. There are sea cucumbers burrowing in the mud, starfish and brittlestars crawling on the surface, and the delicate lattices of moss animals branching alongside sea squirts. Larger soft corals and sponges provide shelter and substrate for a community of smaller invertebrates as well as nursing and feeding grounds for fish and their offspring.

Meanwhile, Greenland’s fisheries are an economic lifeline: seafood from ground fisheries constitutes over 80 per cent of the country’s exports. This fact means the industry often finds itself at odds with the need to protect life on the sea floor. Fisheries for deep-water prawns, offshore halibut and cod use deep-sea trawls that weigh heavily on the seabed, often damaging or destroying fauna as the gear is dragged along. Trawling poses a particular threat to the immobile and long-lived seafloor organisms that are an integral part of the marine ecosystem.

Rising to the conservation challenge

Greenland’s trawl fisheries have been responding to conservation challenges by engaging with green-labelling organizations—such as the Marine Stewardship Council—to implement sustainable strategies to safeguard natural resources and environments. But the deep ocean of the Arctic is one of the least explored and understood places on Earth, and considerable knowledge gaps remain. I am part of a team of marine scientists from the Zoological Society of London (ZSL) and the Greenland Institute for Natural Resources that is trying to fill these gaps by investigating the distribution of seafloor species and how they are affected by trawling.

Underwater cameras allow us to survey the seabed, giving us a unique view of the life there. By examining data from trawl fisheries, we can compare habitats that have been fished in the past (or are being fished now) with non-fished habitats. We often see evidence from trawl fishing in the form of grooves and tracks on the seabed. The results of our research confirm what is widely known in the scientific community: trawled areas are considerably lower in biodiversity and in the abundance of larger organisms.

One of our research challenges is to find habitats in West Greenland that are entirely untouched by fisheries so we can understand what a pristine, untouched area should look like. For example, some areas on the shelf of West Greenland have been fished for cold-water prawns for more than 50 years. Most of the damage usually occurs the first time an area is trawled, and recovery rates are extremely slow. I have spoken with an old fisherman who could remember a time when metre-high corals (of the species Paragorgia) clogged entire nets. But despite our efforts over the past decade, we have not been able to capture on video a single specimen of this potentially tree-sized coral, which suggests they are long gone.

More research needed

As fisheries expand into unexplored areas, pristine habitats face new conservation challenges. In fact, Chris Yesson, a research fellow at ZSL, says that with sea temperatures rising, prawn stocks appear to be migrating further north. Fisheries want to move with them, he notes, but this means moving into new areas and damaging potentially vulnerable seabed habitats.

Under the circumstances, there is a pressing need to conduct more research in these areas (or at least develop sound predictions regarding the presence of vulnerable habitats) to inform management before a fishery enters them.

The Greenlandic culture is strongly connected to the ocean and its resources. The most famous Greenlandic saga about the mother of the sea, Arnaqquassaaq, tells about the connection of people to the sea and the importance of preserving harmony between humans and nature. From her home at the bottom of the sea, Arnaqquassaaq would send up fish, mammals and birds for hunters to catch. If humans failed her, she would stop the supply of food.

I think this saga contains a lot of truth—and potentially a warning. The ocean floor is a rich habitat, providing food and shelter for many commercial fish species and feeding grounds for mammals, such as the walrus. Taking care of the home of the mother of the sea is essential to taking care of ourselves.

Mona Fuhrmann is a post-doctoral researcher at the Institute of Zoology in London, UK with a keen interest in benthic ecology of Arctic ecosystems. She focuses on benthic deep-sea communities in West Greenland, particularly their distribution and diversity and the impacts of trawling.