Comment: In the 2025 documentary film Ocean, narrated by David Attenborough, there’s a clip of a trawl net scouring the sea floor, smashing into everything in its path. Small fish, rays, squid, and other animals try to outswim it, but they can’t; they’re swept into the net and scooped out of the water.
When the net opens on the deck of the trawlers, it spills out a morass of marine life. It’s not clear which species the trawl net was targeting – it’s caught everything. Attenborough’s voiceover tells us that all the unwanted animals will be discarded. “Over three-quarters of a trawler’s catch may be thrown away,” he says. “It’s hard to imagine a more wasteful way to catch fish.”
This is perhaps the only knowledge most people have of bottom trawling – and it doesn’t always look like this, says Rochelle Constantine, a professor in the Faculty of Science at the University of Auckland. “It’s not all, the Attenborough video ploughing through the seabed,” she says. “Yes, that was mostly what happened in the past. It still happens in some places.”
There are better ways of doing things, says Constantine, and more options than outright bans of bottom-trawling or continuing it in its present form in New Zealand waters.
About two-thirds of the commercial catch in New Zealand is bottom trawled. Last month, Seafood NZ chief executive Lisa Futschek told Newsroom that an end to bottom trawling would be an end to the country’s seafood industry.
Meanwhile, Constantine doesn’t want potential improvements to bottom trawling to be ignored or overlooked if the focus is solely on the question of a ban.
“Could we fish better?” asks Constantine. “Could we trawl without destroying habitat and have zero bycatch? Can we look at our legislation or frameworks that are getting in the way of using and developing innovative new technologies?”
Reform legislation to allow innovation in fishing technology
In New Zealand, trawling technology lacks innovation, says Constantine, not because fishers and researchers don’t have good ideas, but because regulations often hamper them from trying those ideas.
One example of a barrier to development is the rule that there can be only two wires connecting a trawl net to a fishing vessel. This rule exists for a good reason: wires are generally dangerous for seabirds attracted to fishing activity.
Fishing vessels are required to scare away seabirds using a range of tactics that need to be fully adopted to be effective. If implemented properly, extra wires could power sensors that would make the trawl net more responsive: sonar that maps fish ahead, depth sensors to help the trawl avoid obstacles including the seabed, cameras to identify what species are in the net. Wireless technologies with net sensors giving real-time data to the fishers are under development – but they are expensive and uptake has been slow.
In future, fishers may be able to choose which species to catch and which to release, while the gear is still underwater – no need to pull up a net filled with unwanted fish.
“There are lots of different technologies and innovations being considered, but the two-wire problem persists, says Constantine. “This has been put to government. The industry’s been waiting for decisions for a few years, but it’s not been important enough.”
Develop new methods of bottom-trawling that are less destructive
Technological innovations have already reduced some of the harm of trawling. A collaboration between Plant and Food Research (now part of the Bioeconomy Science Institute) and three fishing companies produced modified trawl gear now called FloMo, which lands fish on the stern of the vessel surrounded by water, rather than mashed together in the net.
Using FloMo, about 80 percent of non-target fish survive to swim another day, while 20 percent are killed or injured. Meanwhile, target fish are largely in better condition because they haven’t been crushed. “And so, they come up as a higher-value product, they’re in perfect form as very high-price point fish,” says Constantine. “But also, the non-target species that come up can be put back to be part of the ecosystem again.”
FloMo is successfully used in some New Zealand fisheries. The World Wildlife Fund is advocating for it to be approved for use in the United Kingdom, European Union and United States.
Ban especially destructive aspects of bottom trawling
If there’s one place to stop bottom trawling entirely, it’s on seamounts: underwater mountains where many unique communities form and slow-growing species live. “Often they’re in colder water, and things that live in colder waters tend to live longer, they have slower breeding cycles – like the deep-sea corals, which take an extremely long time to form, but they support a lot of biodiversity,” says Constantine. “There’s this huge richness that builds up around seamounts and researchers are always discovering new species.”
That richness includes fish, including commercially valuable species such as orange roughy. But bottom trawling irreparably damages these fragile habitats, harming the corals and other life there. These places may never recover; Constantine says they’re so poorly studied that we don’t know what’s there before it’s gone. “The orange roughy fishery is a good example of the vulnerabilities of these habitats and species and why they should be left alone,” says Constantine. Due to overfishing, several deep-sea orange roughy stocks have collapsed, and have yet to recover their former abundance.
There are strong arguments for banning bottom trawling from seamounts entirely. New Zealand’s continued bottom trawling has attracted international scrutiny. It is the only fleet on the South Pacific high seas actively bottom trawling, “New Zealand is currently the only country that continues this – which comes with a reputational risk,” says Constantine.
Avoid the seabed entirely
The seabed is the biggest store of carbon on the planet, and it’s in our interests to keep it there. We don’t want it to end up as carbon dioxide in the atmosphere, where it causes climate change, or in seawater, where it causes ocean acidification.
But scouring the seabed with an old-fashioned trawl net can release some of that long-term, locked-up carbon. It also churns up sediment, which can smother species that feed by filtering water, like shellfish. The solution: avoid the sea floor.
“There’s bottom trawling that hits the bottom, and a lot of bottom trawling doesn’t anymore,” says Constantine. “It fishes just above the seabed – because the fish are there, yet it’s classified as bottom trawling.”
It’s now possible for sensors on a trawl net to move the net when an obstruction is detected ahead, so the net doesn’t drag along the seabed, destroying marine life and their habitat.
Ideally, we would be able to drop ‘bottom’ from trawling altogether – by specialising in these non-contact forms of the technology. “We shouldn’t be touching the seabed,” says Constantine. “We really shouldn’t.”
Fishing doesn’t have to be stuck in the past
“Trawling on the seafloor is a big impact,” says Simon Thrush, a professor of marine science at the University of Auckland. “If we could transition towards other forms of fishing that were less impactful but also produced a higher-quality product – that would keep fish on the table and the industry in action.”
It requires public and political will. “For all the talk that we’re hearing from our government right now, we want to be technology driven, we want innovation,” says Constantine. “We’ve actually got a number of fishers who want to try these innovations, and researchers who want to bring in new kinds of technologies and trial them here, and we can’t do it with our outdated laws and severe lack of funding and support for innovation in ocean research.”
Constantine envisages a better form of fishing – one that doesn’t indiscriminately catch marine life but targets the right type and size of fish in demand. Imagine, she says, that “every trip that goes out catches exactly the optimal price point fish species or size – and then when we have that in hand, we know that we’ve got exactly what we need, and it’s in such great condition that we’re going to get a higher value.”
It also involves putting the ocean at the centre of the conversation, she says – something that’s been missing from the debate so far. “How do we make sure we have habitat and fish stocks thriving, not just the target species, but biodiversity thriving, because that’s important – it builds in resilience and we know that biodiversity is critical to a healthy planet.”
The world is facing unprecedented environmental challenges. Planetary Solutions, an initiative of the Sustainability Hub at Waipapa Taumata Rau, University of Auckland, and Newsroom, explores these issues – and the practical ways we can all be part of the solution.
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