3D ocean assessments reveal that fisheries reach deep but marine protection remains shallow

Domain: earth_science
Published: 2024-05-21
Editorial outcome: minor_revision

Abstract
The wave of new global conservation targets, the conclusion of the High Seas Treaty negotiations, and the expansion of extractive use into the deep sea call for a paradigm shift in ocean conservation. The current reductionist 2D representation of the ocean to set targets and measure impacts will fail at achieving effective biodiversity conservation. Here, we develop a framework that overlays depth realms onto marine ecoregions to conduct the first three-dimensional spatial analysis of global marine conservation achievements and fisheries footprint. Our novel approach reveals conservation gaps of mesophotic, rariphotic, and abyssal depths and an underrepresentation of high protection levels across all depths. In contrast, the 3D footprint of fisheries covers all depths, with benthic fishing occurring down to the lower bathyal and mesopelagic fishing peaking in areas overlying abyssal depths. Additionally, conservation efforts are biased towards areas where the lowest fishing pressures occur, compromising the effectiveness of the marine conservation network. These spatial mismatches emphasize the need to shift towards 3D thinking to achieve ocean sustainability.

Introduction
Global conservation efforts are about to significantly expand as the United Nations (UN) Convention on Biological Diversity (CBD)’s Kunming-Montreal Global Biodiversity Framework (GBF) has set the course to cover 30% of land and ocean with area-based conservation tools by 20301. In addition, the GBF recognizes that both protected areas and other effective area-based conservation measures (OECMs) can contribute towards area-based conservation targets. OECMs are geographically defined areas that, unlike protected areas, do not have biodiversity conservation as a primary objective, but still achieve biodiversity benefits from their management2. In addition, a legally binding instrument under the UN Convention on the Law of the Sea to protect and sustainably use marine biological diversity in areas beyond national jurisdiction (BBNJ), otherwise known as the High Seas Treaty, has just been concluded. These agreements bring considerable opportunities for marine conservation by increasing coverage targets, by diversifying the types of governance regimes and sectors that can contribute to area-based conservation, and by vastly extending areas that can be conserved. However, they also create new challenges for conservation planning, such as designing area-based conservation tools suited for off-shore, deep, and vertically complex areas3,4, as well as mindfully incorporating OECMs that are often vertically zoned in the conservation network2. Realizing the potential of these agreements requires a shift from a reductionist two-dimensional (2D) representation of the ocean to a three-dimensional (3D) representation of ecosystems, human use, and impacts5–7. This shift is essential to avoid compounding on the weaknesses of the current conservation network, which already fails at achieving ecological representation8, high levels of protection9, and at abating human impacts10.

The ocean is inherently three-dimensional. Unlike on land, life in the oceans spans over a considerable vertical range from the surface to the seafloor, with an average depth of 3800 m. However, apart from recent model-based prioritization studies11–13, assessments of human use14,15 and of conservation achievements8,16 remain two-dimensional. Although the vertical stratification of marine life and human use has long been recognized, multiple factors have led to the persistence of 2D representations. The historical predominance of terrestrial conservation and of land-use management have shaped marine conservation and marine spatial planning, with human use and UN CBD conservation targets mostly allocated in 2D. This approach has remained mostly unchallenged because human activities, scientific research, and conservation have historically been constrained to shallow marine environments where vertical structure is simple17. Besides, the fragmented nature of ocean governance, with multiple sector- and area-specific regimes, hampers a holistic three-dimensional management of the ocean18.

Distinct scientific groups have previously raised awareness on the fact that deep marine ecosystems, such as the mesopelagic, deep reefs, and seamounts, are under increasing human pressures and require dedicated conservation efforts19–21. However, a three-dimensional framework to identify conservation gaps and priority areas across depths is still missing. In particular, while fisheries are the main driver of marine biodiversity erosion22, global assessments of fisheries’ footprint remain two-dimensional14,23–25 and fail to inform on which depths are being targeted26–28. This represents a critical knowledge gap to inform fisheries management and marine conservation because the sensitivity of ecosystems to fishing pressure varies greatly with depth29. Global mapping of marine cumulative impacts14,30 have been instrumental in guiding marine policies by demonstrating the extent and acceleration of the human footprint on the ocean. There is now a need for 3D mapping of the human footprint across space and depth to guide global conservation policy.

Here, we develop a novel mapping framework by overlaying benthic and pelagic depth realms, which captures main ecological units across depths, onto commonly used 2D marine ecoregions31,32. Using this mapping framework, we assess for the first time the 3D ecological representativeness of the global ocean conservation network and conduct the first global assessment of the depth distribution of fishing effort. We then test whether marine protected areas (MPAs) and OECMs are appropriately sited to provide protection to areas under high fishing pressure across both space and depth. Based on our results, we identify conservation gaps, conservation priorities, and provide recommendations on how to account for specificities linked to the three-dimensionality of the ocean in the global conservation agenda.

Results
Uneven conservation effort across depth
Based on the vertical zonation of marine species, habitats, and environmental conditions33–35, we identified eight benthic and four pelagic realms that represent ecological units across depths (Fig. 1).

We found that the distribution of protection coverage (MPAs and OECMs) is uneven across depth realms (Figs. 2 and S3) and ecoregions (Fig. 3). The euphotic (0 to −30 m) is the best protected depth realm, combining the second largest protection coverage (15%, Fig. 2B), the second largest coverage of Ia and Ib protected area categories of the International Union for Conservation of Nature (IUCN) (1.2%), which tend to more strictly regulate human use (see Table S1 for details on IUCN categories), and the most widespread protection across ecoregions (Fig. 3 and S5). By contrast, the abyssal realm has the smallest extent of protection coverage (5.8%) and the smallest coverage of Ia and Ib IUCN categories (0.6%). The BBNJ treaty now provides the legislative framework to increase abyssal protection coverage as 75% of this depth realm occurs in areas beyond national jurisdiction (Fig. 2D). When considering depth realms predominantly occurring within economic exclusive zones (EEZs), lower mesophotic and rariphotic realms are the least protected globally (Fig. 2B) as well as across most of the world’s coastal ecoregions (extending 200 nautical miles off-shore, Fig. 3).

Across all depths, the majority of protection coverage falls under IUCN category VI or unknown (Fig. 2B), which correspond to the lowest levels of protection from human use36. Most 3D realms are covered by less than 1% of Ia and Ib IUCN categories (0.7% as a global average) and one-third by less than 0.1% (Fig. 3), which correspond to the highest levels of protection. The greatest coverage of Ia and Ib IUCN categories is found in the hadal realm (3%), in the Eastern-Indo Pacific (10%), and in polar ecoregions (Arctic and Southern Ocean, 1–2%).

Distribution of fishing activities across space and bathymetry
We assessed the 3D distribution of fishing footprint by overlaying the spatial distribution of fishing activities reported by the Global Fishing Watch (GFW33) with the highest resolution bathymetric map of the ocean37. We found that both fishing pressure and fishing gears are highly structured by bathymetry (Fig. 2A). Areas overlying euphotic to upper bathyal depths experience above average fishing pressure dominated by trawlers, while areas overlying lower bathyal to hadal depths experience lower fishing pressure dominated by drifting longline fisheries (Fig. 2A). Average fishing pressure (hour km−2 year−1, Fig. 2A) and total fishing effort (hours year−1, Fig. 4) are highest in the euphotic. Fishing pressure continuously decreases in areas overlying greater depths, with a sharp six-fold decrease in areas deeper than 1500 m (upper bathyal). However, total fishing effort is as high in areas overlying abyssal depths as in areas overlying mesophotic depths. In ecoregions where average fishing pressure is the highest (Temperate Northern Atlantic and Pacific, Temperate South America), average fishing pressure remains high from areas overlying euphotic to upper bathyal depths, while in off-shore ecoregions and in some coastal ecoregions (e.g., Southern Africa, Australasia) average fishing pressure peaks in areas overlying rariphotic to bathyal depths (Fig. 4).

Although bathymetry alone is insufficient to determine the depths targeted by fishing activities, it can inform on the broader depth range likely impacted by fishing pressure. These indirect impacts occur through vertical connectivity processes, such as migration of organisms, top-down trophic controls, or nutrient transfers38–40; and through by-catch, entanglements, anchoring, fishing debris, or ship collisions41. Concerns are now being raised that mesopelagic fisheries could even affect carbon sequestration in deep-sea sediments by altering the ocean’s biological carbon pump42. As such, in data-poor contexts, relying on the bathymetric distribution of fishing activities can be a first entry point to assess the 3D distribution of fishing impacts.

Elucidating the three-dimensional distribution of fishing activities
The disaggregation level of fishing gears reported in the GFW datasets allows to distinguish between pelagic and benthic fisheries for 55% of the total fishing hours reported from 2018 to 2020. Depths targeted by benthic activities can be determined with accuracy as they match the bathymetry of the fishing location. For pelagic fishing activities, we determined depths targeted based on the typical depth range of the fishing gear reported by the GFW and the bathymetry at the fishing location (Fig. 1, Table S3). We found that benthic fishing effort was greatest in the euphotic and mesophotic (>107 hours year−1) but remained important down to the upper bathyal (2 × 106 hours year−1) and occurred down to the lower bathyal (Fig. 4). Most pelagic activities occurred over lower bathyal to abyssal depths and corresponded to mid-water trawls and drifting longlines.

We found that the 3D footprint of fisheries extends across most depths in most ecoregions of the world. In particular, we found that 37% of total fishing effort overlies depths greater than 300 m and thus directly or indirectly impacts deep marine ecosystems (Fig. 4). This is the result of decades of fishing down the deep as shallow and coastal fish stocks have been depleted from overfishing26–28,43,44. Unfortunately, in addition to being unprofitable if not heavily subsidized45,46, deep fisheries are often unsustainable29,47,48, with high rates of by-catch and long-lasting impact on habitats49,50. Some regions have taken action to limit the depth of fishing activities (e.g., trawling ban below 800 m in European waters), but more depth regulations are needed to ensure sustainable fishing practices27.

Our study is the first attempt to characterize the 3D distribution of fishing activities at the global scale and reflects the limited available knowledge to characterize the 3D fishing footprint. Importantly, about 45% of fishing activities reported in the GFW database do not discriminate pelagic and benthic activities (Fig. 4). Alternatively, datasets that distinguish pelagic and benthic fishing activities, such as those produced by some Regional Fisheries Management Organizations, provide catch data pooled by large spatial units, which also prevents from determining the depth distribution of fishing activities. Systematically distinguishing between pelagic and benthic fishing and increasing the precision of the spatial information associated with catch data would constitute important steps forward to improve our understanding of the depths targeted by fisheries. Our results underestimate fishing pressure overlying euphotic to rariphotic depths because the GFW database only documents vessels with automatic identification systems, which does not capture most small-scale fisheries, especially in the Caribbean, South-West Pacific, and Indian Ocean where catches are systematically underreported23,25.

Mismatched distribution of fishing and conservation efforts
We evaluated whether protection coverage across 3D realms is appropriately sited to mitigate fishing pressure by testing whether MPAs and OECMs are implemented in highly fished realms. We found that the protection coverage of 3D realms (log transformed) was negatively correlated with fishing pressure (Fig. 5), indicating a large bias of ocean conservation towards least impacted areas. This negative correlation was significant when considering coverage by all MPAs and OECMs (p = 0.021, R2 = −0.22), and when considering coverage by only MPAs of Ia/Ib IUCN categories (p < 0.001, R2 = −0.33).

We defined four profiles of conservation priority (Fig. 6b) based on the fishing pressure (below or above median) and protection coverage of 3D realms (behind or past halfway progress from 2020 to 2030 targets). We found that highest conservation priority areas, i.e., areas with low protection coverage and high fishing pressure, mostly occur in the mesophotic, rariphotic, and upper bathyal realms across all ecoregions of the world (Fig. 6a, b). Lowest conservation priority areas, i.e., areas that combine high conservation coverage and low fishing pressure, mostly occur at lower bathyal and abyssal depths in coastal ecoregions. Implementing future MPAs or OECMs in such low use and widely represented areas would decrease the net ecological benefits achievable by these conservation tools. If areas of low fishing pressure still need to be targeted to minimize impacts on fisheries, then targeting 3D realms that suffer from conservation representation gaps should be the priority. Such 3D realms mostly occur in lower bathyal and abyssal depths in off-shore ecoregions and will require conservation action in the high seas (Fig. 6b). Implementing and actively managing MPAs of high protection levels in any 3D realm would provide important conservation benefits, as 90% of 3D realms have still not reached 5% of high protection coverage and 47% cumulate low coverage with high fishing pressure (Fig. 5), therefore falling under the highest priority category (Fig. 6b).

Methods
Definition of three-dimensional marine realms
We obtained a 3D zonation of the ocean by overlaying a 2D zonation of marine ecoregions (e.g., Temperate Northern Atlantic, Tropical Eastern Pacific) with a depth zonation of the main benthic and pelagic realms (e.g., epipelagic, mesopelagic). To define a 2D zonation of marine ecoregions (latitude and longitude), we used the global map of pelagic and coastal realms as described in Spalding et al. (2012, 2007)31,32. Realms (hereafter ecoregions) provide the largest spatial unit with coherent biota at high taxonomic levels resulting from shared environmental conditions and evolutionary history32. This makes ecoregions relevant units to assess biodiversity representation. Ecoregions are divided into 11 coastal ecoregions and four “pelagic” ecoregions (Fig. S1). Coastal ecoregions extend to 200 nautical miles (370 km) offshore or to the 200-m isobath where the later occurs further. As such, coastal ecoregions cover all waters shallower than 200 m, but also areas of bathyal and abyssal depths when the later occur within 200 nautical miles from shore. “Pelagic” ecoregions cover off-shelf pelagic waters, including waters beyond national jurisdiction. Because all ecoregions actually include both pelagic and benthic ecosystems, we referred to “pelagic” ecoregions as “off-shore” ecoregions hereafter to avoid confusion with the distinction between the benthos versus the water column. We used the ecoregions vector layer from the UN-WCMC Ocean Data Viewer77 with a precision of 0.01 degrees.

We defined the zonation of benthic depth realms based on the description of ecological depth zones in the literature33–35,78 as follows: euphotic (0–30 m), upper mesophotic (30–60 m), lower mesophotic (60–150 m), rariphotic (150–300 m), upper bathyal (300–1000 m), lower bathyal (1000–3500 m), abyssal (3500–6000 m), and hadal (below 6000 m). Similarly, we defined the pelagic depth realms as follows: epipelagic (0–200 m), mesopelagic (200–1000 m), bathypelagic (1000–3500 m), abyssopelagic (3500–6000 m), and hadopelagic (below 6000 m).

Three-dimensional distribution of MPAs and OECMs
We used the World Database on Protected Areas (WDPA79), the most comprehensive source on designated protected areas, to build our global map of MPAs80. Similarly, we used the World Database on Other Effective Conservation Measures79 to build our global map of OECMs. We followed the methodology recommended in Thomas et al.80 to process the WDPA vector layer in a way that generates reliable information on the area and protection level of MPAs. Only MPAs for which spatial boundaries were known were included in the analysis. Although circular buffers have been used in the past to include MPAs for which size but not shape is known (e.g., Spalding et al.81, we chose not to do so to avoid false information on the bathymetric coverage of MPAs82. Terrestrial parts of MPAs were excluded by clipping MPA boundaries with a terrestrial land vector (Natural Earth version 5.1.1, 10-m resolution). The MPA vector layer was simplified to a resolution of 0.01 degree to save memory consumption and computation time.

To account for the MPAs' level of protection70 we used the management categories defined by the International Union for Conservation of Nature (IUCN)83 from the WDPA (Table S1). Although the IUCN categories and the level of protection as defined by the MPA Guide do not have perfect correspondence36, the IUCN management categories reflect a gradient from exclusive biodiversity protection (Ia) to integrated human use and extraction (VI), which we used here as a proxy for levels of protection. IUCN categories reported as “Not Applicable”, “Not Reported” or “Not Assigned” were merged into a unique level of protection categorized as “Unknown”.

MPAs resulting from different designation processes can spatially overlap. To avoid double-counting MPA coverage that protect the same area, we only kept the designation providing the highest level of protection for a given area. To do so, we created a unique vector layer for each IUCN level of protection by extracting the corresponding polygons from the original vector layer and merging all polygons. We then subtracted the vector layer of the highest level of protection (Ia) from the vector layer of the second highest level of protection (Ib). We then merged vector layers of Ia and Ib MPAs and subtracted it from the vector layer of the following highest level of protection (II), and so on. Finally, we merged the vector layers obtained, resulting in non-overlapping MPA polygons of the highest level of protection for a given area.

We used bathymetric data from the GEBCO raster layer37 to assess the depth distribution of protection coverage. The depth distribution of MPAs and OECMs was obtained by extracting values from the bathymetric raster for each MPA and OECM polygon and summing the area of cells corresponding to the same depth realm.

This layer used a polar projection (EPSG:4326) and thus the area covered by each cell size varied with latitude. The area of each raster cell was calculated using the following formula:

cell area = cell height × cell width (1)

The height of a cell is constant and equal to:

cell height = resolution in degrees × minutes per degree × meters per minute

with resolution in degrees = 0.004166; minutes per degree = 60’ and meters per minute = 1852 m. This gives a cell height of 463 m.

The width of a cell is equal to:

cell width = earth perimeter(latitude) / nb of cells (2)

with nb of cells = 86,400.

The perimeter of the Earth at a given latitude was calculated as:

earth perimeter(latitude) = 2πR × cos(latitude × π / 180) (3)

with R = 6378 km.

To verify our calculations, we performed a second cell size calculation using the cellSize() function from {terra} and compared the matrix of values obtained from both methods. Results were identical and we chose to keep our formula-based calculation method because of shorter processing time.

The depth realms protected by MPAs or OECMs were determined by the bathymetry of protected cells. The benthic depth realm protected by an MPA or OECM cell corresponded to the bathymetry of that cell, and the pelagic depth realms protected corresponded to all realms occurring between the surface and the seafloor. For example, if a protected cell had a bathymetry of 3000 m, it was assumed to protect the upper bathyal (benthic realm) and the epipelagic, mesopelagic, and bathypelagic (pelagic realms).

We calculated the proportion of benthic protection existing for each benthic realm i as follow:

% benthic protected i = (benthic area protected i / total benthic area i) × 100 (4)

We performed the same calculation for pelagic depth zones.

Three-dimensional distribution of fishing pressure
For the fishing data, we used the most recent (2.0) version of fleet daily fishing activity15 from Global Fishing Watch (GFW) at the highest available resolution (0.01 degree). GFW collects data from publicly available automatic identification system (AIS) and vessel monitoring systems operated by governments. While only 2% of all fishing vessels carry AIS (mostly large, commercial vessels), those vessels are responsible for 50% of the fishing in economic exclusive zones (EEZ) and 80% of the fishing in the high seas15. This dataset was chosen over the FAO global fishing catch dataset because fishing pressure on marine ecosystems is better captured by fishing effort (hours km−2) than catch (ton km−2) data. We analyzed fishing data from the three most recent years available on the GFW as of the 20th May 2022: 2018 to 2020. We found a strong correlation between the number of fishing hours by gear type and bathymetry across these three years (tau = 0.96, p-value < 10−16) demonstrating that results were stable across years. In our figures, we presented values from the 2019 dataset. The inter-annual variability is represented as a 95% confidence interval in Fig. 4. Files tracking the intensity (fishing hours cell−1) and location (latitude and longitude) of daily fleet activities in 2019 were combined into a dataset of 205,656,988 fishing events. Data files were converted to vector shapefiles using spatial coordinates of fishing activities (see Fig. S2) and fishing activities were then attributed to ecoregions and bathymetric ranges. Information on vessels’ gear type was joined to this dataset using the Maritime Mobile Service Identity (MMSI), a unique identification number for vessels.

We assessed the distribution of fishing pressure across depth realms using two approaches: an approach that estimates the broad impacts of fishing activities across depths (hereafter “depth impacted”), and an approach that estimates the depth directly targeted by fishing activities (hereafter “depth targeted”). We considered as impacted by fishing activities all depth realms occurring in the vertical column of that activity, from the surface to the seabed. This assumption is based on empirical and model-based evidence that disrupting one part of the surface-to-seabed continuum has cascading effects on the rest of the continuum because of vertical connectivity processes. Such cascading vertical impacts have been demonstrated between ecosystems as distant as the epipelagic and abyssal benthos84,85.

To determine the depth realms impacted by fishing activities, we used the bathymetric value at the location of fishing activities and determined the benthic and pelagic realms present in that surface-to-seabed column. As such, only one benthic realm can be impacted by each fishing activity, but several pelagic realms can be impacted at once. We calculated the fishing pressure (hours km−2) impacting each benthic depth realm by summing the total hours of fishing activities impacting that benthic depth realm divided by the spatial extent of that depth realm (Fig. 2). Similarly, we calculated the fishing pressure (hours km−2) in each 3D realm (Fig. 4) by summing the total hours of fishing activities impacting a given benthic depth realm within a given ecoregion and dividing it by the spatial extent of that 3D realm (km2).

To determine the depth realms targeted by fishing activities, we relied of the depth range of fishing gears associated with each fishing activity. This method was only achievable for gear types that discriminate pelagic and benthic activities (Table S2). We considered that benthic activities targeted the benthic depth realm corresponding to the bathymetry of the fishing location. We considered that pelagic activities only had a direct impact on pelagic realms within the depth range of the fishing gear used, and within the depth range (i.e., the bathymetry) of the location fished. For example, a pelagic fishing gear with a depth range of 30–350 m operating at a location of 400 m depth was considered to target both the epipelagic (0–200 m) and mesopelagic (200–1000 m) realms, but if the same vessel operated at a location of 150 m, it was considered to only target the epipelagic. To determine the depth range of pelagic gears, we reviewed technical descriptions in published and gray literature (e.g., NOAA, MSC). We checked the information collected by consulting fisheries experts. The depth range of each fishing gear obtained from this literature review is summarized in Table S3.

Three gear types used in the GFW did not discriminate benthic and pelagic activities: “purse seines”, “trawlers” and “fishing”, which represented 62% of the total fishing hours registered. To increase our ability to discriminate benthic and pelagic activities, we contacted managers of the GFW database to access further details on registered trawler vessels, the gear type combining the most unspecified (pelagic vs. benthic) fishing hours. This additional data allowed us to further distinguish between bottom and midwater trawlers and assign an additional 17% of the total fishing hours to benthic or pelagic activities, bringing the total proportion of fishing activities for which the impacted depth could be determined from 38% to 55%. The remaining 45% of fishing hours were categorized as targeting an “unspecified” depth (Fig. 4).

Definition of conservation priority profiles
Relation between protection coverage and fishing pressure was tested using a linear regression model (Pearson method) from the {ggplot} function suite ‘ggpubr’.

Conservation priority profiles were defined based on the fishing pressure and protection coverage occurring within each 3D realm. Four categories of fishing pressure were defined using the quartiles of fishing pressure (hour km−2 year−1) calculated in section 2.3 for 3D realms. Four categories of protection coverage were defined based on the progress toward the achievement of conservation targets. This was calculated first using the CBD target of 30% of total protection coverage by 2030, and then using the target of 10% of high protection coverage by 2030 (e.g., ref. 67). For the first assessment, we distributed 3D realms among four categories of protection coverage: 0–10%; 10–20%, 20–30% and >30%. For the second assessment, we distributed 3D realms among four categories of IUCN Ia/Ib category coverage: 0–2.5%, 2.5–5%, 5–10%, and >10%. For both assessments, we attributed a score to each 3D realm from 1 to 16 reflecting their position in these 4×4 categories (Fig. 5A). We then simplified these 4×4 categories into 2×2 categories using as thresholds the median value of fishing pressure and 20% of total protection (resp. 5% of Ia/Ib protection coverage), which correspond to halfway progress from 2020 to 2030 global conservation targets. The four resulting categories defined different conservation priority profiles for 3D realms: “highest priority” for above median fishing and below halfway completion of conservation targets; “lowest priority” for the opposite scenario; “fills conservation gaps” for below median fishing and below halfway completion of conservation targets and “mitigates fishing pressure” for the opposite scenario.

Software, R packages, and scripts
We carried out all vector and raster operations using the {sf}86 and {terra}87 packages under R Core Team (2021)88. Figures were created using {ggplot2}89 and {tidyr}90, and edited using Illustrator®. QGIS® was used for the preliminary visualization of data and production of Supplementary figures.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript by Jacquemont and colleagues is a very well written summary of the results of an\nanalysis that has not been done before. In short, the compare the areas covered by marine protected\nareas with the world's footprint of fisheries. Their most important finding (from my perspective) is that\n\"the protection coverage of 3D realms (log transformed) was negatively correlated with fishing\npressure (Figure 5), indicating a large bias of ocean conservation towards least impacted areas\"\n(page 8). This is a conclusion that needs to be highlighted everywhere in the manuscript. I would at least\nedit the abstract to make it more clear, and I strongly suggest the authors to highlight this whenever\nthey give interviews about this paper when it's published.\nThe paper does highlight the fact that biologically important areas (mesophotic and rariphotic) are\nheavily impacted and under protected. This is another important finding that may trigger higher\nprotection of those depths. So the article is timely and its publication is needed.\nI don't particularly like the focus on the high seas, as I think the impacts there are still too small and\nthe area is too large, so I would tone that down a bit. But that's just my personal take, so do\nwith it what you will.\nA point that I do think should explicitly be made, perhaps in the conclusions section, is that protecting\nmostly high seas to reach the (completely arbitrary in my view) 30% is a big mistake. And that's\nwhere we are heading.\nI caught one misspelling, UICN (should be IUCN) in figure 5. Other than that, congratulations on a\ngreat manuscript. The analyses all look fine to me, and there is not much else you can do with the\ndata at hand.", "reviewer_2": "The premise and purpose of the paper are excellent. The main idea is that ocean conservation has\ntraditionally been 2 D but needs to be conceived in 3D to protect the ocean, in particular deep waters.\nThe title with its focus on depth of fisheries is part of the story but maybe not the full one. Please\nclarify more clearly why consider protecting waters below 1500 m where most fishing ends. Fishing is\nonly one of multiple uses and stressors that affect deep-ocean ecosystems.\nThe paper has many excellent features that highlight the disconnect between fishing and current\nocean protection. The findings will provide important baseline information for spatial planning to\nachieve 30x30, including in areas beyond national jurisdiction. However, many of the analyses seem\ncomplicated and sometimes non-intuitive. In some cases the terminology used does not accurately\nrepresent the concept (detailed below). The regional designations of coastal and offshore ecoregions\nare confusing and somehow perpetuate the false idea that EEZs don’t host much of the deep sea. If\ncoastal ecoregions cover only continental shelves (which traditionally extend to 200 m depth ) how is\nany actually bathyal or abyssal? Or do they extend 200 miles from shore?\nGeneral Consideration. I find it troublesome to design protection priorities based on current/recent\nfishing effort without mentioning climate change. You acknowledge that fish may change depth with\nclimate but they also will migrate horizontally. At the very least there should be a mention of how\nclimate change-induced redistribution of species (e.g., will low-m and high- use areas remain so?) will\naffect your prioritization and whether there is a way to build this in to planning.\nBelow are considerations and suggestions for clarification.\nSummary\nLine 20-21 this terminology makes no sense – mesopelagic fishing peaking in areas of abyssal depths.\nChange to ‘in areas overlying abyssal depths’.\nLine 30 – can you give some examples of OECMs – are you considering VMEs? APEIs? PSSIs? Or are\nthese on the IUCN categories? Please clarify for those not familiar with the concept.\nLine 33 These agreements also bring new opportunities (not just challenges) – and for purposes of\nthis paper it is better to highlight these.\nLine 41-49. Two points to consider.\n1. It is important to point out that life does not exist very far above the surface on land (maybe 100\nm? 1 km?) but life exists for thousands of meters above the seafloor with an average depth of the\nocean at 3.8 km. This means that most of the habitable volume on the planet is in the (deep) ocean.\n2. UNCLOS has divided international waters into two regimes – the Area (seafloor) managed for\nminerals and the High Seas (water column) managed for fisheries. BBNJ tackles all the rest.\nLine 51 deep sea is only hyphenated when used as a double adjective (e.g. deep-sea fishing)\nFurther, you cannot list deep sea as an ecosystem parallel to mesopelagic reefs or deep coral reefs\n(which I would argue are the same thing). Do you mean deep-sea sediment? Seamounts?\nCanyons? Hydrothermal vents? Methane seeps? Abyssal plains? There are many different deep-sea ecosystems\npresent.\nLine 67 do you mean avoid or minimize fisheries impacts? Or mitigate in the sense of recovery?\nFigure 1. Where is the hadopelagic? This is a valid zone that appears in most textbooks. All\ntrenches have a significant water column.\nLine 91-2. Please replace ‘most’ with a percentage. Are you saying most of the abyssal area is in\nABNJ? Note that 52% of all EEZ area has a seafloor between 2000 and 6000 m and much of this is\nabyssal. So this statement can be misleading.\nLine 94 Use of the term twilight zone for lower mesophotic and rariphotic (60-300 m?) is probably\nincorrect. Standard usage of this term by biological oceanographers refers to the twilight zone as 200-\n1000 m (see Wikipedia). I suggest not using this term.\nFigure 2. This figure has a number of problems.\n-I cannot see vertical dashed lines referred to in the legend.\n- I do not understand the meaning of distance of depth realm values to benchmarks or how to\ninterpret the lollipops. What forms the benchmark?…\n-Most importantly I really think that section D has the legend reversed. As shown you have most of\nthe shallower areas in ABNJ and the deeper areas in the EEZ. Is this correct?\nIUCN Categories – Line 88. The first mention of IUCN is on line 88. You need to both write out the full\nname of the organization – then give the abbreviation. Please explain the categories in the text with\nreference to the table before you start using them. I had no Idea what Ia, Ib, IV etc. were and didn’t\nfind this information until I got to the methods.\nFig. 3 - Legend – what is the bottom of the scale assuming the first color is 0-1. 30 to ?? or label >\n30. Something is wrong with the white areas in this and other figures. Please clarify how far offshore\nthe coastal ecoregions go – is this 200 miles? Is offshore beyond 200 mi? Or determined another way?\nI find this terminology very confusing.\nLine 126 – replace higher with ‘upper’ bathyal… higher bathyal depths would refer to a larger number\nbut I don't think that is what you mean.\nLine 132 Phrasing is confusing – fishing is as high in areas of abyssal depths makes no sense when\nyou say there is no fishing at abyssal depths. All references to this should say ‘in areas overlying\nabyssal seafloor.’\nLine 138 and 144 – ‘Bathymetric distribution’ is not the right term. Refer to depth of seafloor\nunderlying the fishing effort.\nLine 142. Do you mean that mesopelagic fisheries have the potential to alter the carbon cycle? I would\nbe very surprised if there is actual demonstration that this has already occurred.\nLine 160. Note that deep-sea biologists generally consider the deep sea to start below 2000 m It\nwould be great to know what % of fishing effort occurs at depths > 200 m.\nLine 167 – I do not think your study is the first to characterize depths of global fisheries. See Fig. 1 in\nMorato et al. 2006 (Fish and Fisheries 7: 24-34). This is based on catch but does a good job of\nillustrating trends in depth. Also Watson and Morato 2013\nhttps://doi.org/10.1016/j.fishres.2012.12.004\nLine 169 to 170. Change to do not discriminate between..\nLine 170-72. Note that the FAOs RFMOs exist separately for demersal fisheries and for pelagic (mostly\ntuna) fisheries in international waters. Thus management of fisheries and the catch records are\ndistinct for benthic and pelagic in international waters. You did not use their data sets but many\npapers do.\nLine 178 – is drilling about oil and gas? Please be more specific.\nFigure. 5\n-Change UICN to IUCN in the heading top the left panel.\n-Can you explain why protection is on the x axis and fishing is on the y axis? If you considered fishing\nactivity dependent on amount of protection this would make sense… but later in the paper you say this\nis not the case. I think that discussion needs to be moved up to where you first introduce the negative\ncorrelation in Fig. 5. (normally expected) . Since you are trying to argue that high fishing pressure\nshould drive protection I would reverse the axes.\n-Please give R2 values with the P. The liness don’t look like they explain a great deal of the\nvariance.\nFigure 6 assumes static fishing pressure and does not acknowledge other pressures that might occur\nin bathyal and abyssal waters such as from seabed mining or carbon dioxide disposal technologies.\nLine 250 and 253 – the dichotomy between twilight and deep is not appropriate. Typically Twilight is\n200-1000 m and deep is below 200 m so one is a subset of the other.\nLine 261-2 This is an important point. A perfect example is the Cross Chapter Box on\nBiodiversity Hotspots in the IPCC Special Report on Ocean and Cryosphere under climate change. None of the\nhotspots identified occur in the open deep sea.\nLine 265. Recognize the deep sea is not fully mapped with respect to bathymetry and mention the\nSeabed 2030 program goal to fully map the seafloor.\nLine 268 – not just depth shifts but also horizontal.\nLine 296-8. This statement does not apply to hydrothermal vents and seeps where reliance is not on\nsurface production.\nLine 304 - define residual conservation\nLine 308 – Area-based conservation implies 2D. Do we need a new term?\nLine 320-22. I agree that this is important for ABNJ but remember that 75% of EEZs are in deep water\n(>200 m) and this is where the largest fishing pressure is.\nLine 345 – really should include hadopelagic. If you look up papers in google scholar you will see that\nthis zone (water in trenches) is a real thing with much research.\nLine 361 – Introduce Table S1 near the start of the paper.\nLine 416 to 418. If you are only tracking 50% of fishing in EEZs what sort of fishing are you missing…\nis there a particular bias? Can you compare your data set to catch depths?\nFigure S1. The colors are generally hard to decipher, especially the very dark color does not\ndistinguish ocean from continents.\nFigure S2. Suggest adjusting the slide color scale so more of the fishing activity is visible.\nFigure S3. Where is the hadopelagic?\nFig. S4. This is very confusing… How can abyssal sites be such a small percent of most realms. If the\nfirst 12 columns are for coastal waters and the last for offshore waters this needs to be labeled and\nexplain the zones. But it seems even then that abyssal systems are underrepresented. Throughout the\npaper I have found these designations confusing.\nFigure S5. What are the left and right panels? Same data with different color scales?\nTable S1. Clarify fishing status\nTable S2. Dredge fishing entry has a typo\nTable S3 why list hadal before abyssal? A. Are you sure there is no abyssal fishing? B.\nWhy no hadopelagic?", "reviewer_author_response": "Response to reviewers\nReviewer #1\nReviewer #1: The manuscript by Jacquemont and colleagues is a very well written summary of the\nresults of an analysis that has not been done before.\nReply: We deeply thank the reviewer for his/her appreciation of our work, and for pointing out its novelty\nand clarity.\nReviewer #1: In short, they compare the areas covered by marine protected areas with the world's\nfootprint of fisheries. Their most important finding (from my perspective) is that \"the protection coverage\nof 3D realms (log transformed) was negatively correlated with fishing pressure (Figure 5), indicating a\nlarge bias of ocean conservation towards least impacted areas\" (page 8). This is a conclusion that needs to\nbe highlighted everywhere in the manuscript. I would at least edit the abstract to make it more clear, and I\nstrongly suggest the authors to highlight this whenever they give interviews about this paper when it's\npublished.\nReply: We thank the reviewer to help us identify key messages. We have now modified the abstract\naccordingly and will keep that in mind when communicating on our research. The new sentence in the\nabstract reads as: “Importantly, we found that conservation effort is heavily biased towards areas where\nleast fishing pressures occur, compromising the effectiveness of the marine conservation network\nglobally.” (line 22-23)\nReviewer #1: The paper does highlight the fact that biologically important areas (mesophotic and\nrariphotic) are heavily impacted and under protected. This is another important finding that may trigger\nhigher protection of those depths. So the article is timely and its publication is needed.\nReply: We thank again the reviewer for his appreciation of our study.\nReviewer #1: I don't particularly like the focus on the high seas, as I think the impacts there are still too\nsmall and the area is too large, so I would tone that down a bit. But that's just my personal take, so do\nwith it what you will. A point that I do think should explicitly be made, perhaps in the conclusions\nsection, is that protecting mostly high seas to reach the (completely arbitrary in my view) 30% is a big\nmistake. And that's where we are heading.\nReply: While we believe that emphasizing the importance of our framework and findings in the context\nof the recent BBNJ agreement is important, we agree that improving the conservation status within\nnational jurisdictions is equally important and that protecting the high seas should not be used to deviate\nfrom national targets within National Biodiversity Strategy Action Plans. We have now rephrased the\nconclusion to emphasize the importance of conservation in EEZs, and tone down our focus on the high\nseas alone, as suggested: “Such considerations are extremely important for national conservation\nstrategies, as 75% of the world’s EEZs consist of deep ecosystems while concentrating the highest levels\nof fishing pressure. In parallel, the recent conclusion of the High Seas treaty offers a unique opportunity\nto build upcoming conservation efforts on a revised framework that accounts for the complex and\nintricately connected three-dimensional ocean space.” (line 353-355)\nReviewer #1: I caught one misspelling, UICN (should be IUCN) in figure 5. Other than that,\ncongratulations on a great manuscript. The analyses all look fine to me, and there is not much else you\ncan do with the data at hand.\nReply: Thank you for catching this mistake. It has now been rectified.\nReviewer #2\nReviewer #2: The premise and purpose of the paper are excellent. The main idea is that ocean conservation has\ntraditionally been 2D but needs to be conceived in 3D to protect the ocean, in particular deep waters.\nReply: We deeply thank the reviewers for his strong appreciation of our work.\nReviewer #2: The title with its focus on depth of fisheries is part of the story but maybe not the full one.\nPlease clarify more clearly why consider protecting waters below 1500 m where most fishing ends.\nFishing is only one of multiple uses and stressors that affect deep-ocean ecosystems.\nReply: We agree that other stressors and use affect the deep ocean, but as they are not assessed in this\nstudy, we believe that it is more adequate to conserve a title that reflects our study’s focus. We chose to\nfocus on fisheries as they are considered the greatest direct anthropogenic threat to marine ecosystems\n(IPBES, 2019), and because they represent the threat that area-based conservation tools most commonly\nregulate. The main argument to protect waters below 1,500 m is twofold. First, due to the vertical\nconnectivity across the water column, epipelagic fishing in > 1,500m deep waters will affect indirectly the\nfunctioning of these deep water pelagic and benthic systems. Second, fishing activities are targeting\ndeeper and deeper areas, hence protecting 3D areas before fishing occurs is an important strategy for\nbiodiversity conservation. These arguments are explained in the manuscript:\n- Line 158-160: “These indirect impacts occur through vertical connectivity processes, such as\nmigration of organisms, top-down trophic controls or nutrient transfers 38–40; and through by-\ncatch, entanglements, anchoring, fishing debris or ship collisions 41.”\n- Line 327-333: “This assumes that impacts from human use remain compartmentalized to the\ndepths where they occur, which overlooks numerous connectivity processes across depths. The\ncomplex energy, nutrient and population exchanges from the epipelagic to the benthos 75,76 imply\nthat disturbing one depth realm will likely have cascading effects on any other depth of that\nsystem 40. This is true for shallow but also for most deep ecosystems, which almost exclusively\nrely on the biomass and productivity originating from epi- and mesopelagic realms 6,38.”\nReviewer #2: The paper has many excellent features that highlight the disconnect between fishing and\ncurrent ocean protection. The findings will provide important baseline information for spatial planning to\nachieve 30x30, including in areas beyond national jurisdiction.\nReply: We thank the reviewer for pointing out the implications of our work, which is what guided us.\nReviewer #2: However, many of the analyses seem complicated and sometimes non-intuitive. In some\ncases the terminology used does not accurately represent the concept (detailed below). The regional\ndesignations of coastal and offshore ecoregions are confusing and somehow perpetuate the false idea that\nEEZs don’t host much of the deep sea. If coastal ecoregions cover only continental shelves (which\ntraditionally extend to 200 m depth) how is any actually bathyal or abyssal? Or do they extend 200 miles\nfrom shore?\nReply: We agree that this terminology can lead to confusions, and that it was not explained clearly\nenough in the original manuscript. Coastal ecoregions as defined by Spalding et al., (2007) extend indeed\nto 200 nautical miles offshores, or to the 200m isobath if the later occurs further. This is why coastal\necoregions include bathyal and abyssal depths, although the area of abyssal depths is very small in coastal\necoregions (see Figure S4). We have now added a clear description of the boundaries of coastal\necoregions:\n- in the Method section “Ecoregions are divided into 11 coastal ecoregions and four “pelagic”\necoregions (Fig. S1). Coastal ecoregions extend to 200 nautical miles (370 km) offshore or to the 200-m\nisobath where the later occurs further. As such, coastal ecoregions cover all waters shallower than 200\nm, but also areas of bathyal and abyssal depths when the later occur within 200 nautical miles from\nshore.” (lines 367-371)\n- at the first mention of coastal ecoregion in the main text: “…as well as across most of the world’s\ncoastal ecoregions (extending 200 nautical miles offshore, Figure 3).” (lines 110-111)\n- in Figure 3, 4 and 6., the text “within 200 nautical miles” and “beyond 200 nautical miles” was added to\ndescribe coastal vs. offshore ecoregions.\nReviewer #2: General Consideration. I find it troublesome to design protection priorities based on\ncurrent/recent fishing effort without mentioning climate change. You acknowledge that fish may change\ndepth with climate but they also will migrate horizontally. At the very least there should be a mention of\nhow climate change-induced redistribution of species (e.g., will low-m and high- use areas remain so?)\nwill affect your prioritization and whether there is a way to build this in to planning.\nReply: We thank the reviewer for highlighting this important consideration. Because the spatial units (3D\necoregions) we used for our analyses are extremely large, we believe that most climate-induced shifts in\nspecies distribution and in turn in fishing effort distribution would not affect our findings. Even if species\nmigrated by several degrees of latitude, and of tens of meters of depth, they would largely remain in the\nsame 3D ecoregions. However, this would be an important consideration when applying our framework to\nlocal contexts, for which a finer spatial resolution would likely be adopted. We have now added the\nfollowing paragraph in our manuscript to address these points: “Furthermore, climate-induced shifts in\nspecies distributions (Pinsky et al., 2020) and in turn in fishing effort distribution (Palacio Abrantes et\nal., 2022; Cheung et al., 2010) should be accounted for to ensure that protection is targeted towards\nareas of high priority now and under future climate conditions. While species and fishing effort\nredistribution are unlikely to alter the findings of this study given the large spatial extent of 3D\necoregions, this consideration should be reckoned by studies applying this framework at a finer spatial\nresolution.” (lines 254-259). The citations we have added in this paragraph are the following:\nCheung, William WL, Vicky WY Lam, Jorge L. Sarmiento, Kelly Kearney, R. E. G. Watson, Dirk Zeller, and\nDaniel Pauly. \"Large‐scale redistribution of maximum fisheries catch potential in the global ocean under climate\nchange.\" Global Change Biology 16, no. 1 (2010): 24-35.\nPalacios‐Abrantes, Juliano, Thomas L. Frölicher, Gabriel Reygondeau, U. Rashid Sumaila, Alessandro Tagliabue,\nColette CC Wabnitz, and William WL Cheung. \"Timing and magnitude of climate‐driven range shifts in\ntransboundary fish stocks challenge their management.\" Global change biology 28, no. 7 (2022): 2312-2326\nPinsky, Malin L., Rebecca L. Selden, and Zoë J. Kitchel. \"Climate-driven shifts in marine species ranges: Scaling\nfrom organisms to communities.\" Annual review of marine science 12 (2020): 153-179.\nReviewer #2: Below are considerations and suggestions for clarification.\nSummary\nLine 20-21 this terminology makes no sense – mesopelagic fishing peaking in areas of abyssal depths.\nChange to ‘in areas overlying abyssal depths’.\nReply: We modified the abstract as suggested.\nReviewer #2: Line 30 – can you give some examples of OECMs – are you considering VMEs? APEIs?\nPSSIs? Or are these on the IUCN categories? Please clarify for those not familiar with the concept.\nReply: We have not considered these area-based management tools, or any other, as potential OECMs.\nWe have only worked on OECMs already declared by countries and reported in the World Database on\nOECMs, as reviewed in Claudet et al., (2022): “Avoiding the misuse of other effective area-based\nconservation measures in the wake of the blue economy” One Earth 5: 969-974. We have now added a\ndefinition of OECM at the beginning of the introduction “OECMs are geographically defined areas that,\nunlike protected areas, do not have biodiversity conservation as a primary objective, but still achieve\nbiodiversity benefits from their management, such as bottom-contact fishery closures.” (lines 35-37)\nReviewer #2: Line 33 These agreements also bring new opportunities (not just challenges) – and for\npurposes of this paper it is better to highlight these.\nReply: We fully agree that highlighting opportunities is a more powerful approach than only highlighting\nchallenges. We have now added this sentence: “These agreements bring considerable opportunities for\nmarine conservation, by vastly extending areas that can be conserved and by diversifying the types of\ngovernance and sectors that can contribute to conservation.” (lines 39-42)\nWe also replaced: “Addressing these challenges requires (...)” by “Realizing the potential of these\nagreements requires (...)” (line 45).\nReviewer #2: Line 41-49. Two points to consider.\n1. It is important to point out that life does not exist very far above the surface on land (maybe 100 m?\n1 km?) but life exists for thousands of meters above the seafloor with an average depth of the ocean at 3.8\nkm. This means that most of the habitable volume on the planet is in the (deep) ocean.\n2. UNCLOS has divided international waters into two regimes – the Area (seafloor) managed for minerals\nand the High Seas (water column) managed for fisheries. BBNJ tackles all the rest.\nReply: Thank you for these considerations.\n1. We have now addressed this point by adding this sentence: “Unlike on land, life in the ocean\nspans over a considerable vertical range from the surface to the seafloor, with an average depth\nof 3,800 m.” (lines 51-52)\n2. We added this sentence to highlight challenges linked to the sectoral driven governance of the\nocean: “Besides, the fragmented nature of ocean governance, with multiple sector- and\narea-specific regimes, hampers a holistic three-dimensional management of the ocean.”\n(lines 61-62)\nReviewer #2: Line 51 deep sea is only hyphenated when used as a double adjective (e.g. deep-sea\nfishing)\nReply: Thanks. We have corrected the hyphenation of “deep sea” accordingly.\nReviewer #2: Further, you cannot list deep sea as an ecosystem parallel to mesopelagic reefs or deep\ncoral reefs (which I would argue are the same thing). Do you mean deep-sea sediment? Seamounts?\nCanyons? Hydrothermal vents? Methane seeps? Abyssal plains? There are many different deep-sea ecosystems\npresent.\nReply: We thank the reviewer for this point out, we had mistakenly written “mesopelagic reefs”\ninstead of “the mesopelagic”, and we also agree that we cannot list the deep sea as an ecosystem parallel\nto deep reefs. We have now rephrased accordingly : “...deep marine ecosystems, such as the mesopelagic,\ndeep coral reefs, and seamounts, are under increasing human pressures…” (line 64).\nReviewer #2: Line 67 do you mean avoid or minimize fisheries impacts? Or mitigate in the sense of\nrecovery?\nReply: We rephrased to more adequately describe our goal: “We then test whether marine protected\nareas (MPAs) and OECMs are appropriately sited to provide protection to areas under highest fishing\npressure.” (lines 80)\nReviewer #2: Figure 1. Where is the hadopelagic? This is a valid zone that appears in most textbooks. All\ntrenches have a significant water column.\nReply: We have now added the hadopelagic pelagic realm in Figure 1.\nReviewer #2: Line 91-2. Please replace ‘most’ with a percentage. Are you saying most of the abyssal area is in\nABNJ? Note that 52% of all EEZ area has a seafloor between 2000 and 6000 m and much of this is\nabyssal. So this statement can be misleading.\nReply: Yes, most of the abyssal area is in the ABNJ. We have replaced “most” with “75%”. (line 107)\nReviewer #2: Line 94 Use of the term twilight zone for lower mesophotic and rariphotic (60-300 m?) is\nprobably incorrect. Standard usage of this term by biological oceanographers refers to the twilight zone as\n200-1000 m (see Wikipedia). I suggest not using this term.\nReply: The term “twilight zone” has been used on and off by the mesophotic research community, but we\nagree that it is not ideal given it is also used by biological oceanographers to refer to the pelagic zone at\n200-1000 m. We have removed this term throughout the manuscript and replaced it by “mesophotic and\nrariphotic”.\nReviewer #2: Figure 2. This figure has a number of problems.\n- I cannot see vertical dashed lines referred to in the legend.\n- I do not understand the meaning of distance of depth realm values to benchmarks or how to interpret the\nlollipops. What forms the benchmark?…\n-Most importantly I really think that section D has the legend reversed. As shown you have most of the\nshallower areas in ABNJ and the deeper areas in the EEZ. Is this correct?\nReply:\n- There are four vertical dashed lines, one in panel A at x=0.2, and three in panel B at x=0.7, x=10\nand x=30. We believe that they are dark enough to be easily readable, and wonder if a formatting\nissue occurred during submission.\n- the legend in section D was indeed reversed, we thank the reviewer very much for spotting this\nmistake. We have now rectified this error.\n- we have rephrased the legend of Figure 2 to explain more clearly how to interpret lollipops and\nbenchmarks. Benchmark values correspond to the vertical dashed lines in the figure, standing for\n2020 and 2030 CBD targets, global average high protection coverage, and global average fishing\npressure. Green and red lollipops indicate positive and negative “status” of depth realms in regard\nto fishing and conservation averages or targets, i.e., negative if experiencing above average\nfishing pressure or below average protection coverage. The legend of Figure 2 now reads as\nfollow: “The four vertical dashed lines represent from left to right: average fishing pressure\nacross depths, average coverage of high protection (MPAs of Ia and Ib IUCN categories) across\ndepths, and the 2020 and 2030 CBD coverage targets. Red and hollow, or green and filled\nlollipops indicate (i) whether fishing pressure in each depth realm is above or below average\nfishing pressure across depths, respectively; and (ii) whether the current protection coverage of\ndepth realms is behind or ahead of the average coverage of high protection and of the 2020 CBD\ntarget.” (lines 120-123)\nReviewer #2: IUCN Categories – Line 88. The first mention of IUCN is on line 88. You need to both\nwrite out the full name of the organization – then give the abbreviation. Please explain the categories in\nthe text with reference to the table before you start using them. I had no Idea what Ia, Ib, IV etc. were and\ndidn’t find this information until I got to the methods.\nReply: We have added the full name of the organization at its first mention, and a reference to Table S1\nin that same sentence: “(see Table S1 for details on IUCN categories)” (line 103). Throughout the text,\nwe now specify that categories Ia and Ib “tend to more strictly regulate human use” (line 103).\nReviewer #2: Fig. 3 - Legend – what is the bottom of the scale assuming the first color is 0-1. 30 to ?? or\nlabel > 30. Something is wrong with the white areas in this and other figures. Please clarify how far\noffshore the coastal ecoregions go – is this 200 miles? Is offshore beyond 200 mi? Or determined another\nway? I find this terminology very confusing.\nReply: We have modified the scale labels to indicate >30 as suggested in Figure 3, and have performed a\nsimilar modification in Figure 4. We have now added in Figure 3,4, and 6 text that clarifies the\nboundaries of coastal vs. offshore ecoregions.\nReviewer #2: Line 126 – replace higher with ‘upper’ bathyal… higher bathyal depths would refer to a\nlarger number but I don't think that is what you mean.\nReply: We thank the reviewer for pointing out this mistake, we replaced ‘higher” with “upper”.\nReviewer #2: Line 132 Phrasing is confusing – fishing is as high in areas of abyssal depths makes no sense\nwhen you say there is no fishing at abyssal depths. All references to this should say ‘in areas overlying\nabyssal seafloor.’\nReply: We have now applied this suggestion throughout this paragraph.\nReviewer #2: Line 138 and 144 – ‘Bathymetric distribution’ is not the right term. Refer to depth of\nseafloor underlying the fishing effort.\nReply: We have now removed this formulation throughout this paragraph, including in paragraph titles.\nTitles now read as “Distribution of fishing activities across space and bathymetry” instead of\n“Bathymetric distribution of fishing activities”; and “Elucidating the three-dimensional distribution of\nfishing activities” instead of “From bathymetric to three-dimensional distribution of fishing activities”.\nReviewer #2: Line 142. Do you mean that mesopelagic fisheries have the potential to alter the carbon\ncycle? I would be very surprised if there is actual demonstration that this has already occurred.\nReply: After re-examining the literature, we toned down our statement to: “Concerns are now being\nraised that mesopelagic fisheries could even affect carbon sequestration in deep-sea sediments by\naltering the ocean’s biological carbon pump” (lines 160-162).\nReviewer #2: Line 160. Note that deep-sea biologists generally consider the deep sea to start below 2000\nm It would be great to know what % of fishing effort occurs at depths > 200 m.\nReply: We have run a new analysis to determine the % of fishing effort occurring below 200 m (37%)\nand now include this result (lines 177-178).\nReviewer #2: Line 167 – I do not think your study is the first to characterize depths of global fisheries.\nSee Fig. 1 in Morato et al. 2006 (Fish and Fisheries 7: 24-34). This is based on catch but does a good job\nof illustrating trends in depth. Also Watson and Morato\n2013 https://doi.org/10.1016/j.fishres.2012.12.004\nReply: Yes, we acknowledge the work conducted by Morato and colleagues, and have cited both these\npapers in our manuscript. We agree that the original sentence is incorrect, and have changed it to : “Our\nstudy is the first attempt to characterize the 3D distribution of fishing activities” (line 185).\nReviewer #2: Line 169 to 170. Change to do not discriminate between..\nReply: We have modified this sentence accordingly, as well as any other occurrence of this formulation\nthroughout the manuscript.\nReviewer #2: Line 170-72. Note that the FAOs RFMOs exist separately for demersal fisheries and for\npelagic (mostly tuna) fisheries in international waters. Thus management of fisheries and the catch\nrecords are distinct for benthic and pelagic in international waters. You did not use their data sets but\nmany papers do.\nReply: We thank the reviewer for bringing this point to our attention. Unfortunately, FAOs RFMOs\ndatasets are not spatialized (usually present total catch values across large management units, with no\ncoordinates associated with fishing activities), so while the distinction between pelagic and demersal\nfisheries is useful, depth cannot be determined. This is why we did not use these datasets (nor the Sea\nAround Us datasets) for this analysis.\nWe have expanded our original sentence to reflect these challenges: “Importantly, about 45% of fishing\nactivities reported in the GFW database do not discriminate pelagic and benthic activities (Fig. 4).\nAlternatively, datasets that distinguish pelagic and benthic fishing activities, such as those produced by\nRegional Fisheries Management Organizations, provide catch data across large spatial units, which also\nprevents from determining the depth distribution of fishing activities. Systematically distinguishing\nbetween pelagic and benthic activities and increasing the precision of the spatial information associated\nwith catch data would constitute important steps forward to improve our understanding of the depths\ntargeted by fisheries.” (lines 187-194)\nReviewer #2: Line 178 – is drilling about oil and gas? Please be more specific.\nReply: Yes, oil, gas, and natural gas liquids. We have now specified “hydrocarbon drilling” (line 253).\nReviewer #2: Figure. 5\n- Change UICN to IUCN in the heading top the left panel.\n- Can you explain why protection is on the x axis and fishing is on the y axis? If you considered fishing\nactivity dependent on amount of protection this would make sense… but later in the paper you say this is\nnot the case. I think that discussion needs to be moved up to where you first introduce the negative\ncorrelation in Fig. 5. (normally expected). Since you are trying to argue that high fishing pressure\nshould drive protection I would reverse the axes.\nReply: We have rectified the misspelling of IUCN, and inverted axes in Figure 5 and in the legend of\nFigure 6 as suggested.\nReviewer #2: -Please give R2 values with the P. The lines don’t look like they explain a great deal of the\nvariance.\nReply: We have now added R2 values along with p-values.\nReviewer #2: Figure 6 assumes static fishing pressure and does not acknowledge other pressures that\nmight occur in bathyal and abyssal waters such as from seabed mining or carbon dioxide disposal\ntechnologies.\nReply: We restricted the scope of this study to protection coverage and fishing pressure, as fishing is\nrecognized as the greatest direct anthropogenic threat to marine biodiversity (IPBES, 2019), and because\nthey are one of the threats that marine conservation tools are most readily able to mitigate. We state\nexplicitly in the title of our study and in the title of figures that we only consider fishing pressure. We\nhave now also added two sentences recognizing that other pressures exist and should be accounted for to\noperationalize our framework: “Here, we restricted our 3D conservation prioritization to two variables:\nprotection coverage and fishing pressure. While fishing pressure is considered as the main direct\nanthropogenic threat to marine life, other human pressures could be considered to translate our\nframework into actionable recommendations, especially given the projected rapid expansion of offshore\nrenewable energies, hydrocarbon drilling and deep-sea mining.” (lines 249-254)\nReviewer #2: Line 250 and 253 – the dichotomy between twilight and deep is not appropriate. Typically\nTwilight is 200-1000 m and deep is below 200 m so one is a subset of the other.\nReply: As stated above, this term has been entirely removed from our manuscript.\nReviewer #2: Line 261-2 This is an important point. A perfect example is the Cross Chapter Box on\nBiodiversity Hotspots in the IPCC Special Report on Ocean and Cryosphere under climate change. None\nof the hotspots identified occur in the open deep sea.\nReply: We thank the reviewer for this relevant example to support our point. We have now added this\nexample in our manuscript line 296.\nReviewer #2: Line 265. Recognize the deep sea is not fully mapped with respect to bathymetry and\nmention the Seabed 2030 program goal to fully map the seafloor.\nReply: We have now added “relying on well-described geophysical features such as depth, which is\nunderway to be fully mapped by 2030,... ” (lines 297), as well as a reference to the Seabed 2030 program\nin that sentence (Mayer et al., 2018. \"The Nippon Foundation—GEBCO seabed 2030 project: The quest\nto see the world’s oceans completely mapped by 2030.\" Geosciences 8).\nReviewer #2: Line 268 – not just depth shifts but also horizontal.\nReply: We only mention vertical shifts in this sentence because we focus specifically on processes for\nwhich depth representation can provide a “climate-smart” advantage, and this is not as clearly the case for\nhorizontal shifts. However, we now mention horizontal shifts in species distribution and fishing effort in\nour discussion of potential impacts of climate change to our prioritization result (lines 254-259).\nReviewer #2: Line 296-8. This statement does not apply to hydrothermal vents and seeps where reliance\nis not on surface production.\nReply: We have changed the phrasing to “...for most deep ecosystems, which almost exclusively rely on\nthe biomass and productivity originating from the epi- and mesopelagic realms” to account for the fact\nthat hydrothermal vents and seeps do not rely on surface production. (line 330)\nReviewer #2: Line 304 - define residual conservation\nReply: We define residual conservation at its first mention: “it is rather the symptom of residual\nconservation by which protected areas are placed where they least interfere with human use” (line 312-\n313).\nReviewer #2: Line 308 – Area-based conservation implies 2D. Do we need a new term?\nReply: Because we advocate for seafloor to surface conservation strategies, we believe that the term\n“area-based conservation” is still relevant. We fear that volume-based conservation might incentivize\nvertically zoned protection. However, complementing spatial indicators with depth indicators could be a\nrelevant shift to improve ecological representation. We have now added these sentences: “Second,\nindicators used to track the ecological representativeness of marine conservation networks should\ninclude a depth dimension in addition to commonly used 2D units, such as ecoregions 16. The 3D\necoregion typology (depth realm x ecoregion) developed in this study could serve as the framework to set\ngoals and track progress towards 3D ecological representativeness. The number of depth realms\nconsidered and their depth limits could be further adjusted at the regional scale to account for local\necological specificities.” (lines 303-308)\nReviewer #2: Line 320-22. I agree that this is important for ABNJ but remember that 75% of EEZs are in\ndeep water (>200 m) and this is where the largest fishing pressure is.\nReply: We have revised our conclusion to incorporate this important consideration: “In the wake of a\nglobal push for more and better ocean conservation to reach Kunming-Montreal GBF targets, the full\nthree-dimensional range of marine biodiversity needs to be represented in proposed conservation\nnetworks. Such considerations are extremely relevant for national conservation strategies, as 75% of\nthe world’s EEZs consist of deep ecosystems while concentrating the highest levels of fishing pressure.\nIn parallel, the recent conclusion of the High Seas treaty offers a unique opportunity to build\nupcoming conservation efforts on a revised framework that accounts for the complex and intricately\nconnected three-dimensional ocean space.” (lines 353-355).\nReviewer #2: Line 345 – really should include hadopelagic. If you look up papers in google scholar you\nwill see that this zone (water in trenches) is a real thing with much research.\nReply: We have added as suggested “hadopelagic (below 6000 m)” to the pelagic realms and modified\nthe depth range of the abyssopelagic to “3500-6000 m”. (line 383)\nReviewer #2: Line 361 – Introduce Table S1 near the start of the paper.\nReply: Table S1 is now introduced L104.\nReviewer #2: Line 416 to 418. If you are only tracking 50% of fishing in EEZs what sort of fishing are\nyou missing… is there a particular bias? Can you compare your data set to catch depths?\nReply: We recognize biases due to incompleteness of fishing activity datasets, and describe it line194-\n198: “Our results underestimate fishing pressure overlying euphotic to the rariphotic depths because the\nGFW database only documents vessels with automatic identification systems, which does not capture\nmost tropical small-scale fisheries, especially in the Caribbean, South-West Pacific and Indian Ocean\nwhere catches are systematically underreported 22,24.” Unfortunately, catch data suffers from similar\nlimitations. A lot of the world’s small-scale fisheries, especially in tropical areas, are simply unreported.\nReviewer #2: Figure S1. The colors are generally hard to decipher, especially the very dark color does\nnot distinguish ocean from continents.\nReply: We have changed the color scale to allow for an easier identification of ecoregions, and switched\ncontinents to a white coloring.\nReviewer #2: Figure S2. Suggest adjusting the slide color scale so more of the fishing activity is visible.\nReply: We have adapted our slide color scale and the spatial grid to make fishing activities more visible.\nReviewer #2: Figure S3. Where is the hadopelagic?\nReply: We have now re-analyzed data taking into account the hadopelagic zone, and present the full\nresult in the new Figure S3.\nReviewer #2: Fig. S4. This is very confusing… How can abyssal sites be such a small percent of most\nrealms. If the first 12 columns are for coastal waters and the last for offshore waters this needs to be\nlabeled and explain the zones. But it seems even then that abyssal systems are underrepresented.\nThroughout the paper I have found these designations confusing.\nReply: We have now labeled coastal and offshore ecoregions as suggested. Area of depth realms were\nlog-transformed in this figure, which is why abyssal systems might seem underrepresented.\nReviewer #2: Figure S5. What are the left and right panels? Same data with different color scales?\nReply: The left panel is for total coverage by all IUCN categories and OECMs, and the right panel is for\nhigh levels of protection only (Ia/Ib IUCN categories). We had forgotten to add this important\ninformation in the legend, and have now added it.\nReviewer #2: Table S1. Clarify fishing status\nReply: IUCN categories do not have specific guidelines regarding fishing regulations. This is why IUCN\ncategories cannot be perfectly linked to levels of protection as defined by the MPA guide. As explained in\nthe paper, IUCN categories Ia/Ib tend to correspond to higher levels of protection with stricter fishing\nregulations, while other categories tend to have relaxed to no fishing regulations.\nReviewer #2: Table S2. Dredge fishing entry has a typo\nReply: Thank you, the typo has been rectified.\nReviewer #2: Table S3 why list hadal before abyssal? A. Are you sure there is no abyssal fishing? B.\nWhy no hadopelagic?\nReply: Abyssal should be before hadal, we corrected this mistake. After a thorough search on current\nfishing depths and discussion with fishing experts, the lower limit of fishing activities currently occurs at\naround ~ 3000 m for the deepest bottom trawlers. So to the best of our knowledge, no fishing occurs in\nthe abyssal, and if so it would be extremely rare activities. We now have added “hadopelagic” in Table\nS3B, although no pelagic fishing currently occurs that deep.\nReviewers' Comments:\nReviewer #1:\nRemarks to the Author:\nThe authors conducted a very thorough review of their manuscript. It reads even better now, and is\nmore focused. They followed all of my suggestions, and I have no further comments.\nReviewer #2:\nRemarks to the Author:\nI have reviewed the author rebuttal and revised ms and found that the authors have thoroughly and\ncarefully addressed all of the concerns, mistakes, and opportunities pointed out in my original review.\nI thank them - they now have a very valuable contribution.\nThere are a very minor few points that remain to consider:\nFig. 2 caption. Lollipop explanation still confusing – perhaps separate the explanation for Panels A\nand B.\nLine 178 is this correct \"we found that 37% of total fishing effort overlies depths greater than 300 m\"?\nor do you mean 200 m? as stated in rebuttal letter. Either is ok - but please check what you have is\ncorrect and not a typo.\nUse of the term High Seas Treaty (in abstract and elsewhere) is misleading, although many use this\nterminology. ‘high seas’ is the UNCLOS term for the ocean water column in areas beyond national\njurisdiction – but the treaty referred to also includes the seafloor (the Area). I think ‘BBNJ Agreement’\nis more suitable – but the authors prefer High Seas treaty they should at least define this more clearly\nsomewhere. This might seem like a small point but I have already seen state representatives\nmisinterpret the treaty coverage (to not include the seafloor) based on the term 'high seas treaty'.\nAbstract - to be more accurate I suggest you say conclusion of the treaty NEGOTIATIONS rather than\nconclusion of the high seas treaty (it didn't conclude).\nAlso the authors may be interested in this interactive app which show how much of each EEZ occurs at\nwhat water depths.\nhttps://bit.ly/DeepSeaEEZ . There are quite a few major fishing countries that have A LOT of abyssal\nwaters in their EEZs (Peru, Japan, Philippines etc.)\nREVIEWERS' COMMENTS\nReviewer #1 (Remarks to the Author):\nThe authors conducted a very thorough review of their manuscript. It reads even better now, and is more focused.\nThey followed all of my suggestions, and I have no further comments.\nREPLY: We thank Reviewer 1 for their appreciation of our revision.\nReviewer #2 (Remarks to the Author):\nI have reviewed the author rebuttal and revised ms and found that the authors have thoroughly and carefully\naddressed all of the concerns, mistakes, and opportunities pointed out in my original review. I thank them - they now\nhave a very valuable contribution.\nREPLY: We thank Reviewer 2 for their appreciation of our revision.\nThere are a very minor few points that remain to consider:\nFig. 2 caption. Lollipop explanation still confusing – perhaps separate the explanation for Panels A and B.\nREPLY: The explanation of lollipop interpretation has been separated for panels A and B as suggested. The legend\nnow reads: “Figure 2. Distribution of fishing pressure and conservation efforts across depth realms. (A) Average\nfishing pressure by fishing gear across depth realms. Lollipops indicate whether fishing pressure in each depth\nrealm is above (red lollipops) or below (green lollipops) global average fishing pressure. (B) Protection\ncoverage of MPAs (by IUCN categories) and OECMs across depth realms. Lollipops indicate whether the current\nprotection coverage of depth realms is behind (red lollipops) or ahead (green lollipops) of the average\ncoverage of high protection and of the 2020 CBD target.”\nLine 178 is this correct \"we found that 37% of total fishing effort overlies depths greater than 300 m\"? or do you mean\n200 m? as stated in rebuttal letter. Either is ok - but please check what you have is correct and not a typo.\nREPLY: We did mean 300 m indeed. We thank the reviewer for pointing this out.\nUse of the term High Seas Treaty (in abstract and elsewhere) is misleading, although many use this terminology.\n‘high seas’ is the UNCLOS term for the ocean water column in areas beyond national jurisdiction – but the treaty\nreferred to also includes the seafloor (the Area). I think ‘BBNJ Agreement’ is more suitable – but the authors prefer\nHigh Seas treaty they should at least define this more clearly somewhere. This might seem like a small point but I\nhave already seen state representatives misinterpret the treaty coverage (to not include the seafloor) based on the\nterm 'high seas treaty'.\nREPLY: To avoid any confusion, we now added in the introduction: “a legally binding instrument under the UN\nConvention on the Law of the Sea to protect and sustainably use marine biological diversity in areas beyond national\njurisdiction (BBNJ), otherwise known as the High Seas Treaty” L35-37\nAbstract - to be more accurate I suggest you say conclusion of the treaty NEGOTIATIONS rather than\nconclusion of the high seas treaty (it didn't conclude).\nReply: We added “negotiations” L2 as suggested.\nAlso the authors may be interested in this interactive app which show how much of each EEZ occurs at what water\ndepths.\nhttps://bit.ly/DeepSeaEEZ . There are quite a few major fishing countries that have A LOT of abyssal waters in their\nEEZs (Peru, Japan, Philippines etc.)\nReply: Thank you for sharing this resource."}, "author_response": ""}]

Decision letter