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How Seabed Mapping Can Help Guide High-Seas Conservation

It took more than two decades of tireless hard work, but for those involved in the process, it was all worth it. On March 4, 2023, diplomats from almost two hundred governments agreed on the United Nations Treaty of the High Seas to protect the ocean, tackle environmental degradation, fight climate change, and prevent biodiversity loss.

Better known as the “High Seas Treaty” or “Biodiversity Beyond National Jurisdiction (BBNJ) Treaty,” the moment has been hailed by many, including Virginijus Sinkevičius, Commissioner for Environment, Oceans and Fisheries at the European Commission, as “a historic moment for our Oceans…With the agreement on the UN High Seas Treaty, we take a crucial step forward to preserve the marine life and biodiversity that are essential for us and the generations to come.”




Once formally adopted, the High Seas Treaty will become a legally binding instrument under the United Nations Convention on the Law of the Sea (UNCLOS), the international agreement that lays out the obligations and rights of countries undertaking any activity at sea. When brought into force in 1994, UNCLOS came with provisions for protecting, conserving, and managing the marine environment and marine life. However, those provisions have been criticised for being insufficient, particularly for marine life and habitats in the high seas, the part of the ocean that lies outside any country’s jurisdiction. The High Seas Treaty aims to readdress this balance.

The Treaty paves the way for several new mechanisms. A dedicated international high seas authority with an intergovernmental Conference of Parties as its executive, and a scientific and technical committee, will be established to enact the Treaty. It focuses on numerous principles and provisions, particularly those relating to the collection and sharing of marine genetic resources, environmental impact assessments, capacity-building and technology transfer, and the designation of marine protected areas and other area-based tools to protect high seas marine life and habitats.

Once adopted, the Treaty will not automatically result in marine protected areas. Rather, countries must work together to implement them. Even when all mechanisms are in place, one crucial question will remain. Where should marine protected areas be created in the high seas, so they are most effective? To answer this question, we need seabed mapping.




While en route from Seattle, Washington, to the Gulf of Alaska for a seabed survey in May 2023, the crew of the U.S research vessel Okeanos Explorer took the opportunity to map a known seamount just 645 kilometres off the coast of British Columbia, Canada. “Before our multibeam sonars pinged the seafloor here, the peak of the seamount was recorded at around 1,592 meters (5,223 feet) under the surface on older NOAA nautical charts,” Logan Kline, NOAA Ocean Exploration Knauss Fellow wrote on her ’Live From the Field’ expedition blog. “Now that we’ve collected more data, we know that the peak on this seamount exists at around 895 meters (2,936 feet) below the surface”. The Okeanos Explorer didn’t have the opportunity to map the whole seamount, so there is a chance it could be even taller.

Seamounts—active, dormant, or extinct underwater volcanoes—are a fascinating find for any seabed mapper. Their detection is also, of course, essential for safe navigation at sea. They are also a hotspot for myriad marine life. Some will pass their entire life on the slopes, in the nooks and crannies of a seamount. Some may be frequent visitors, some less so. Seamounts, and other seabed features, such as hydrothermal vents and ridges, are known biodiversity hotspots. Other subtler seabed features, such as furrows, sediment waves, landslide scars, and erosional troughs, also create a home for diverse marine life. Seabed mapping at high resolution is essential for finding the features that may support thriving communities in need of protection. The next part of the process is identifying and mapping the biological communities.

In May 2023, HSH Prince Albert II of Monaco announced that 24.9 percent of the seabed had been mapped. While there is still much work to be done to bring this number up, 24.9 percent is already orders of magnitude greater than the >1% of the deep sea that has been biologically sampled.

We can’t protect what we don’t know exists, nor can we wait until we have fully mapped the seafloor and the vast diversity of communities that thrive in the depths. The solution? Use the best available data and tools to predict where they may be.




April 2023 saw the launch of the joint Nippon Foundation – Nekton Ocean Census project, a ten-year mission which aims to identify 100,000 new marine species. The project is ambitious, but if previous large-scale missions are anything to go by, the knowledge gathered will be invaluable.

Over twenty years ago, the Census of Marine Life began a ten-year quest to assess the abundance, distribution, and diversity of marine life. That programme is now over, but it left lasting legacies. In 2020, some of those legacies led to the Challenger 150 initiative, a global cooperative for deep-sea biological research. “Challenger 150 is about a lot of things, but it’s fundamentally about collaborating on various aspects of deep-sea science,” says Professor Kerry Howell, head of the Deep Sea Conservation Research Unit at the Marine Institute (Plymouth University), and co-lead of the Challenger 150 UN Ocean Decade Programme.

Increasing the number of biological observations and samples in the deep sea is one of Challenger 150’s priorities. Another is to create predictions of where species are most likely to be. “The intention will be to take our standardised collected biological datasets and then use them with GEBCO outputs to generate basin-scale distribution models for key species and habitats,” Howell explains.

Species distribution models use environmental (and sometimes biological) factors, known as predictor variables, to predict where a species is most likely to be found. “We collect data on where species are in the deep sea, and then we look at the depth, the temperature, salinity, whatever data is available, understand the conditions it likes to live under. If we have data or where [the species] isn’t found, we can use that to look at the conditions it doesn’t like to live in,” explains Howell. “We then feed [that data] into the model and get out a prediction on how likely it is that our species will be found in a particular location.” For species that live on the seafloor, bathymetry “is one of the most important predictor variables in species distribution models,” says Howell.

Bathymetry provides several key pieces of information relevant to distribution modelling, often acting as a proxy for other factors that we don’t have direct measurements for. First and foremost, there is depth. “It’s not because depth is important, but because things that vary with depth are important, but they vary across depth in a consistent way,” explains Howell, highlighting temperature and light availability as factors that are important for marine life and that vary consistently with depth.

Then there are the other elements that come from bathymetric data. “Steep slopes tend to be rocky, non-sedimented areas. They also tend to have faster currents going over them,” says Howell as an example. “We’ll often derive bathymetric position index, which is a measure of whether you’re on a topographic high or in a topographic depression, or on a flat bit of seabed. These serve as a proxy for the things species like,” explains Howell. For example, Howell notes that depressions tend to collect organic material within them, which is important for deposit feeders, such as lugworms or sea cucumbers.

“I wouldn’t attempt distribution modelling for benthic species without bathymetry data, which is why I always say we can’t do our job without The Nippon Foundation-GEBCO Seabed 2030 Project doing their job.”




As part of the goal to map the entire seafloor by 2030, Seabed 2030 have set target resolutions for the mapping, which vary by depth (the deepest depths are coarser than the shallower depths due to current practical limitations in seabed mapping). For species distribution modelling, the push for high-resolution mapping data will help create more accurate predictions.

Where available, Howell prefers to use ship-mounted multibeam bathymetry data at scales of a few hundred metres for modelling purposes as they provide “ecologically relevant data…This sort of scale gives you useful models that you can make management decisions on,” Howell says, adding that people map for different reasons, so there isn’t one single scale that is fit for all purposes and for all scenarios.

For those areas that haven’t yet been mapped with multibeam, the bathymetry data is invariably much coarser. These data can still be used to create prediction maps, albeit at scales that may be less than ideal for management. Still, such data is far from useless. Coarse prediction maps are better than no maps. Coarse (and indeed finer scale) prediction maps can highlight areas in particular need of exploration.

Indeed, in an ideal world, decisions would be based on actual observations of what lies beneath the sea surface, “but that will take a lot of time. So, in the interim, why would you not use the best available scientific data, which are distribution models,” says Howell. Certainly, species distribution models may not be perfect, but as more seabed data becomes available and the number of biological observations increases, those distribution models will only get better.