Abstract
Oil and gas are among the most important non-renewable energy sources globally, and recent technological advancements have accelerated offshore exploration, especially in Africa. Countries like Nigeria, Sudan, Algeria, and Egypt are major players, with Algeria, Nigeria, and Egypt among the top ten nations with substantial liquefied natural gas (LNG) capacities. West Africa, once underrepresented in the sector, has gained prominence with the 2016 discovery of the Greater Tortue Ahmeyim (GTA) reserve, located between the maritime borders of Senegal and Mauritania. The emergence of this new sector could significantly alter the region's approach to managing its marine resource. The GTA project unfolds in four stages exploration, construction, exploitation, and decommissioning all of which pose environmental risks. These include habitat destruction, pollution from discharges, noise, species displacement or death, light pollution, and the degradation of nesting, feeding, and breeding grounds. Sessile species are particularly vulnerable. However, there is a less studied dimension of the implications of this new sector. The development of these phases requires the displacement of other activities, particularly fishing, leading to knock-on effects that also warrant consideration. The complexity introduced by this emerging marine sector necessitates a holistic assessment of its implications for the region's present and future development. Integrated Ecosystem Assessment (IEA) are widely used to inform ecosystem-based management (EBM). Using the ODEMM (Options for Delivering Ecosystem-Based Marine Management) approach, the study identifies the interconnections between sectors, environmental pressures, and ecological components. A modification of the ODEMM framework, distinct from previous applications (focusing on a single sector), was made during our analysis to better highlight the effects of the GTA project in our study area. Results showed that this new sector has several impacts on ecological components, increasing certain existing pressures and introducing new ones. Despite these negative impacts, positive effects, such as the use of platforms as artificial coral reefs, were also observed.
1 Introduction
Since the 1950s, there has been a steady increase in global energy consumption () driven by the high use in urbanization and industrialization, which has led by to the rapid depletion of onshore reserves (Shukla and Karki, 2016). Faced with this situation and knowing that about 80% of global energy comes from fossil fuels, with nearly 80% of these fuels being oil and gas (), the oil and gas industries are seeking new reserves in the ocean particularly in deep and ultra-deep waters (; Shukla and Karki, 2016). More than 7,000 offshore oil and gas platforms have been built in 53 countries around the world with over 150,000 kilometers of underwater installations (e.g., pipelines; ; Patin, 2018; Techera and Chandler, 2015). Among these, 40 countries produce significant quantities of offshore oil and gas (Parente et al., 2006). However, the need for new non-renewable energy reserves and the shift from onshore to offshore research are accelerating the peak oil and gas phenomenon first described in 1956 by Marion King Hubbert. This term means that oil and gas production reach its maximum (high point) before beginning to decline toward zero due to the depletion of reserves.
In recent years, the search for new reserves of non-renewable offshore energy has expanded in Africa, particularly in its western region (Vaghi, 2014). A significant offshore gas reserve, known as Greater Tortue Ahmeyim (GTA) was discovered in 2016 at the maritime border between Senegal and Mauritania ().
The GTA project features the deepest underwater infrastructure in Africa and an agreement for the equitable sharing of tasks and revenues was signed by the governments of both countries in December 2018 (). The exploitation and export of this gas reserve, initially planned for 2022, started on the 31th of December, 2024 due to several delays including the covid 19 pandemic.
Senegal and Mauritania are part of the Canary Current Large Marine Ecosystem (CCLME) region, one of the largest eastern boundary upwelling ecosystems in the world (; ; ; Osemwegie et al., 2022). The CCLME spans the exclusive economic zones (EEZs) from Morocco to Guinea, including the archipelagos of Cabo Verde and the Canary Islands ().
This area has a very high level of primary production () and contain various types of habitats such as coral reefs, canyons, knolls, seamounts, estuaries and mangrove forests (). Several cold water reefs of Lophelia (Desmophyllum pertusum) are located between 430 and 648 meters (; Moctar et al., 2024; Ramos et al., 2017) one of which is near the pipeline corridor of GTA project. Wetlands (estuary and mangrove forest) are also found in the lower delta of the Senegal river with 1,000 hectares of mangrove forests as well as a small area in the south of Mauritania (; ; Taïbi et al., 2014). In addition to their roles as floods protector and blue carbon reserves, these mangrove forests are a source of income for the local population primarily for women through activities such as oyster collection and processing (Sarr et al., 2016). A protected marine area known as the Saint-Louis MPA (Sarr et al., 2016) is also located in this region just a few kilometers from the hub floating liquefied naturel gas (FLNG).
The CCLME serves as a migration route for several species of marine mammals, seabirds and reptiles. For instance, marine mammals such as Delphinus delphis, Physeter macrocephalus, Balaenoptera edeni, Balaenoptera musculus have been observed in this region (; ; ; ; Samba Bilal et al., 2023) and reptiles such as green turtles (Chelonia mydas) which migrate from the Bijagós Archipelago (Guinea-Bissau) to northern Mauritania (Patrício et al., 2022). In this part of north-west African, and thanks to the national parks of Djoudj (Senegal) and Diawling (Mauritania), several species of birds mainly migratory can be found particularly during the period from November to March (Thiao, 2009). Among them we can mention Anas acuta, Limosa limosa, Phoenicopterus minor, Pelecanus onocrotalus, Dendrocygna viduata (; ).
Several small pelagic fish such as Madeiran sardinella (Sardinella maderensis), round sardinella (Sardinella aurita), cunene horse mackerel (Trachurus trecae), anchovy (Engraulis encrasicolus), bonga shad (Ethmalosa fimbriata) and sardine (Sardina pilchardus) also inhabit the CCLME area [; , ; Sarre et al., 2024]. The stocks of some of these species expand, contract and migrate influenced by the upwelling phenomenon ().
More precisely, the two regions of these two countries where the GTA project is operating are Saint-Louis located on the northern coast of Senegal 400 kilometers north of the capital Dakar () and Trarza located in the southwest of Mauritania (Mohamed, 2012).
In Saint-Louis, fishing (particularly artisanal fishing) is one of the main sectors for local population with landings of 627.650 tons valued at 143 billion FCFA from 2012 to 2022 and an average of 1,444 motorized canoes recorded (). Sardinella spp. are the most captured species () and represent a key resource for the local coastal communities, supporting thousands of livelihoods, including fish processing and related activities (; Thiao, 2009; Thiaw et al., 2017). Others activities are practiced also near the Senegal river such as agriculture (Maillard, 2018; ). In Mauritania, the round sardinella, cunene horse mackerel, chub mackerel (Scomber japonicus), and sardine were the dominant small pelagic species in the catches in 2017, constituting 21 percent, 19 percent, 15 percent, and 20 percent respectively of the total catch of small pelagic [].
The operation of this gas sector consist of four phases: (i) exploration: activities to search for oil and gas using seismic waves (ii) construction: all construction activities for production following the discovery of oil and gas reserves such as drilling wells, laying pipelines, setting up floating production storage and offloading (FPSO) and constructing breakwaters (iii) exploitation: the entire duration of oil and gas production and transportation and (iiii) decommissioning: all dismantling activities once the operation is completed. Offshore gas production is not without consequences for the local population and the marine ecosystem through the release of organic matter, contaminants (Neff, 2002), noise () or catastrophic accidents and the GTA will certainly not be an exception.
This article has three objectives: list (1) all the pressures generated and all the ecological components affected by the GTA project during its four phases, (2) to assess the impact risk of those pressure-ecological component linkage chain and (3) to show how the introduction of this new sector will produce changes in the existing pressures from other sectors.
2 Method
2.1 Study area
2.1.1 Regions
Saint-Louis (Senegal) and Trarza (Mauritania) are the regions in these two countries most concerned with the GTA project (Figure 1).
Figure 1
Saint-Louis is located 400 kilometers north of Dakar with an area of 19,241 square kilometers and a population of 1,204,863. Trarza is located in the southwest of Mauritania with an area of 67,800 square kilometers and a population of 311,261. Ndiago is the commune of Trarza located about 10 kilometers from the floating liquefied natural gas (FLNG) hub.
Before the arrival of the GTA project, several human activity sectors were present in this region including agriculture, fishing, aquaculture, shipping, land-based industry and coastal infrastructure. However, fishing was the main sector practiced by a large portion of the population.
This subregion is characterized by different types of seabeds such as muddy, rocky, sandy and sandy-silty.
2.1.2 Greater tortue ahmeyim (GTA)
The GTA project consists of three main facilities: (1) Wells located about 120 kilometers (-17.746 E; 16.356 N) from the Senegalese-Mauritanian coast at a depth of 2,850 meters, (2) an FPSO located 80 kilometers (−16.883 E; 16.069 N) from the wells at a depth about 120 meters deep and (3) a hub FLNG located 10 kilometers (−16.603 E; 16.065 N) from the coast and at a depth of 30 meters. These facilities are connected by a subsea network of more than 300 kilometers of pipelines and umbilical cables. For safety purposes, each facility is equipped with an exclusion zone with a radius of 500 meters.
Based on the above, we defined our study area as a quadrilateral bounded by the following coordinates: (−16.3°E; 16.5°N), (−16.4°E, 15.8°N), (−18.1°E, 16.0°N), and (−17.8°E, 16.8°N). This area includes the northern Senegalese maritime area (Saint-Louis) and the southern Mauritanian area (Trarza-Ndiago; Figure 1). Our choice is based on the fact that the pressures arising from the GTA project are unlikely to extend beyond this area. Even if some pressures exceed the indicated boundaries, their impacts will be minimal as most of them will mix with water and be diluted as they move away from the area where they are produced (Neff et al., 2011; Smith et al., 1994; Strømgren et al., 1995).
2.2 Methodology
For this work, we used the ODEMM method (Options for Delivering Ecosystem-based Marine Management) which involves building a framework of links or connections based on the DPSIR logic (Driver-Pressure-State-Impact-Response) for a given area (; ; Pedreschi et al., 2023).
This method consists of three steps: (1) identifying the different types of sectors in the study area, (2) listing all the pressures generated by each sector which helps identify their threats, and (3) identifying all the ecological characteristics or components that will be affected by these pressures (; Pedreschi et al., 2023; Skein et al., 2022). A scoring system is then applied based on three criteria: spatial overlap, frequency, and degree of impact.
Here are the definitions of the three criteria listed above (; Pedreschi et al., 2023; Piet et al., 2014; Skein et al., 2022) adapted from Robinson et al. (2013):
Spatial overlap refers to the spatial overlap between a pressure type and an ecological component based on five points: no overlap, site, local, widespread patchy and widespread even.
Frequency refers to the temporal overlap between a pressure type and an ecological component in terms of month based on four points: rare, occasional, common and persistent.
Degree of impact refers to the severity of an interaction between a pressure type and an ecological component. It can be low, chronic or acute.
All these categories have an assessment number that produces the impact risk and more detailed explanation can be found in Annex 1.
In our case study, the ODEMM framework was slightly modified to address the specific characteristics of the gas sector. Specifically, we added two pressures: flaring and light, that are not included in the standard ODEMM framework.
2.3 Data collection
The data collection was done in three steps:
Expert Consultation: experts from institutions such as the Oceanographic Research Center of Dakar-Thiaroye (CRODT), the Mauritanian Institute of Oceanographic Research and Fisheries (IMROP), Cheikh Anta Diop University of Dakar (UCAD), BACoMaB (Banc d'Arguin and Coastal and Marine Biodiversity Trust Fund) and the Instituto Español de Oceanografía (IEO-CSIC) reviewed the standard ODEMM list of pressures and ecosystem components and made modifications where necessary.
Literature Review: relevant scientific literature, reports, and environmental assessments were analyzed to identify existing data on pressures and their impacts on marine ecosystems.
Stakeholder Interviews: structured interviews were conducted with key stakeholders, including local fishermen and British Petroleum (BP) employees, to gain insights into the expected and observed impacts of the GTA project.
All questions asked during our interviews focused on the nature of the impact of the GTA project, the potential pressures that would be generated, the areas affected and their intensity, as well as the species and habitats impacted.
2.4 Data analyses
Our analysis was carried out in three steps: (i) firstly, we conducted an ODEMM for all sectors present in our study area before the GTA project (ii) then we applied the same method but considered offshore gas as the sole sector (iii) and finally we conducted another ODEMM combining all sectors (those present before the GTA project and oil and gas sector).
For step (ii), we separated the analysis into four phases to obtain clearer and more precise results: exploration, construction, exploitation and decommissioning. All ecological pressures and components were considered during the analysis. However, depending on the phase some pressures may be absent (e.g., flaring, which occurs in the construction and exploitation phases but not in the exploration and decommissioning phases). The analyses were then carried out using Rstudio software.
The modification of the ODEMM framework introduced in step (ii) allows for a clearer and more precise assessment in our analysis, specifically highlighting the effects of the GTA project in our study area across the different phases mentioned above. It also enables us to evaluate the influence of the GTA project on pre-existing activities by combining the different sectors involved.
2.5 Construction of sector–pressure–ecosystem linkage chain and score calculation according to ODEMM
The selection of sectors, pressures, and ecological components was not random but was validated through expert consensus from each region and supported by scientific literature, impact assessment reports, and interview data. In cases of disagreement, discussions were conducted until a common agreement was reached among the experts. Together with these experts, we first listed all sectors considered to be present in the study area, then identified the pressures generated by these sectors, and finally determined the ecological components impacted.
The most impactful sector is identified as the one that generates the greatest number of pressures and whose pressures have the highest impact on ecological components.
It is important to note that a single pressure can be generated by several sectors, and its overall intensity depends on how many times it is produced across sectors and the magnitude of its impact on ecological components. The same logic applies to ecological components: one or several components can be affected by multiple pressures originating from different sectors.
The impact risk is first calculated for each individual linkage chain by multiplying the values of the different score categories. Then, for the same sector, the impact risks from different linkage chains (for the same pressure or ecological components) are summed. Finally, the same summation procedure is applied across all sectors.
In summary, summed impact risks are used to obtain pressure-level totals, ecological component rankings, sector rankings, and to weight the flows in the Sankey diagrams.
For both the original ODEMM method and our modified application (focused on one sector at a time), the aggregation logic described above remains the same.
Reproducibility and Modifications to the Script
The R script used is based on the original ODEMM method script published in the reference article (Pedreschi et al., 2019).
The primary difference between the two R scripts lies in sector filtering. In the multi-sector script, no filtering is applied, and all sectors present in the dataset are included in the Sankey diagram. In the single-sector script, an implicit or explicit filter is applied to include only the sector of interest. The same procedure is used to generate both the ranking tables and the Sankey diagrams, but note that for the analysis, the Excel file is saved in CSV format for the Sankey diagrams and in XLSX format for the ranking tables.
No other changes were made to the original ODEMM methodology, and all steps strictly follow the logic of the published method.
3 Results
3.1 All sectors before GTA
We identified 7 sectors generating 18 pressures and impacting 23 ecological components. A complete list can be found in Annex 2. Industrial fishing is the sector with the greatest impact being responsible for several pressures that affect almost all ecological components. It is followed by shipping, artisanal fishing, agriculture, coastal infrastructure, land-based industry and aquaculture, all of which also show strong interconnections (Figure 2).
Figure 2
Regarding pressures, litter has the greatest impact on the ecological components. This pressure is produced by all seven sectors in significant quantities. Next, we have contaminating compounds primarily produced by shipping and agriculture followed species extraction, by catch and abrasion which are largely driven by industrial fishing, all of which are also significant.
Reptiles are the most affected ecological component, followed by seabirds and marine mammals. These three are largely affected by pressures such as litter, contaminating compounds and bycatch. Saltmarshes, demersal and pelagic species are also significantly affected. We also observed that in terms of ecological components, species groups are more impacted than habitats.
3.2 ODEMM for the gas sector
In the second step, we focused solely on the gas sector which has four phases. Depending on the phase, the number of pressures may vary and two new pressures absent in the all sectors are noted here such as non-living resources and flaring. Likewise, several pressures noted in the all sectors ODEMM are absent during this step (e.g., bycatch, species extraction). The number of ecological components remains unchanged.
3.2.1 Exploration
During this period, we considered noise as the only significant pressure, which is why we didn't create a sankey diagram. Marine mammals are the most impacted ecological component due to the seismic waves.
3.2.2 Construction
This phase (Figure 3) presents the greatest number of pressures (13). The top five pressures include noise which is the greatest pressure. It is produced throughout our study area during the drilling of wells, laying of pipelines, anchoring of the FPSO and construction of the breakwater which rises from the seabed and is made up of 21 blocks, each 33 m high. Noise is also generated by ships and helicopters used for routine activities or for transporting personnel. It is followed respectively by siltation/smothering caused by contact between human activities and seabed, sealing due to habitat loss from the breakwater construction and death of sessile species, abrasion from well perforation and dredging and contaminating compounds from accidentals hydrocarbon spills and wastewater discharge. Flaring, invasive species and incidental loss are much less important pressures.
Figure 3
Marine mammals are the most affected ecological component due to the strong presence of noise pressure followed by shallow sediment which is the most impacted habitat. The breakwater to protect the FLNG hub from bad weather is constructed at this level at a depth of 30 m, along with the installation of piles for anchoring the FLNG hub. Next, we identified reptiles, demersal and deep-sea species, given that the majority of activities in this phase occur on or near the seabed. Pelagic species, littoral sediment, mangroves and saltmarshes are the least impacted.
3.2.3 Exploitation
We identified 11 pressures during this phase (Figure 4): contaminating compounds is by far the pressure with the greatest impact affecting almost all ecological components. It is generated by the discharge of gray water as well as the accidental loss of hydrocarbons at the wells, FPSO and FLNG hub. This is followed respectively by noise produced by installation machines, gas tankers and ships during routine activities; light from the FPSO and the FLNG hub which can affect seabirds and reptiles specially at night; wave exposure which will only be modified by the breakwater and litter produced by the accidental loss of work materials and discharges from personnel residing on the FPSO or FLNG hub. Flaring is the pressure with the least impact because it is rarely produced and only in cases of necessity.
Figure 4
Reptiles and seabirds are the most impacted species particularly by contaminating compounds which can accumulate and be harmful in the long term, noise leading to displacement, light which poses a risk of collision or disorientation and wave exposure which causes the loss of nesting sites through erosion. This is followed by littoral sediment which is the most impacted habitat. In this phase we noted that pelagic species are more affected than demersal species. Except the littoral sediment, species are once again more impacted than habitats.
3.2.4 Decommissioning
The results of this phase are somewhat similar to those of the construction phase in terms of pressures with 10 pressures identified (Figure 5). Noise is the pressure with the greatest impact, producing the same effects as listed above, followed by siltation/smothering caused by the removal of facilities, abrasion from well closure and the removal of FLNG hub piles, contaminating compounds from produced water and wave exposure due to its action in the littoral. Incidental loss is the pressure with the least impact as the number of ships will decrease and the speed of ships used for decommissioning will be moderate.
Figure 5
Shallow sediment is the ecological components most affected primarily by abrasion pressure followed by reptiles and seabirds. We also noted that species living on or near the bottom are most affected than pelagic species.
3.3 ODEMM combination
For the final step, we aimed to understand which pressures would be increased or decreased by the arrival of the new gas sector in combination with the pre-existing sectors. We chose the same three phases as in the gas sector (construction, exploitation and decommissioning phase) because the exploration phase had only one significant pressure (noise).
3.3.1 All sectors plus construction phase (first combination)
We combined all existing sectors before the GTA project (Figure 2) with its construction phase (Figure 3).
We observed that the gas sector ranked fifth ahead of coastal infrastructure, land-based industry and aquaculture (Figure 6) with a strong production of noise, siltation/smothering, sealing and abrasion.
Figure 6
Regarding pressures, the five top pressures are respectively litter, contaminating compounds, noise, species extraction and abrasion with considerable effects on the ecological components. The effects of these pressures are the same as those previously described.
Reptiles, seabirds and marine mammals are respectively the most impacted ecological components. Likewise demersal species are more affected than pelagic species.
3.3.2 All sectors plus exploitation phase (second combination)
We combined all existing sectors before the GTA project (Figure 2) with the exploitation phase (Figure 4).
The gas sector ranks 7th just ahead aquaculture sector (Figure 7) with a strong production of contaminating compounds pressures.
Figure 7
Litter, contaminating compounds, species extraction, bycatch and abrasion are the five greatest pressures. These pressures present a strong impact on the ecological component.
Reptiles and seabirds are respectively the most impacted ecological components specially by litter (primarily produced by industrial fishing sector) as well as contaminating compounds bycatch and incidental loss. Next, marine mammals are largely impacted by litter and incidental loss. Demersal fish and saltmarshes/estuaries occupy the 4th and 5th positions respectively.
3.3.3 All sectors plus decommissioning phase (third combination)
Here, we combined all existing sectors before the GTA project (Figure 2) with its decommissioning phase (Figure 5). Our first observation is that these results are similar to the second combination meaning they are not many changes between these two phases.
The gas sector ranks 7th just above aquaculture, similar to the second combination (Figure 8) with a strong production of noise pressures.
Figure 8
Litter, contaminating compounds, species extraction, abrasion and bycatch are the five greatest pressures. These pressures present a strong impact on the ecological component.
Reptiles and seabirds are respectively the most impacted ecological components followed by marine mammals which are largely affected by litter and incidental loss. Demersal fish and saltmarshes/estuaries occupy the 4th and 5th positions respectively.
3.3.4 Comparison (between all sectors and each of the GTA phases)
Our case study has demonstrated that, with the exception of non-living resources and flaring, all other pressures generated by the GTA project were pre-existing and have since intensified in magnitude.
During the operation of this new sector (GTA) and depending on these different phases, noise and contaminating compounds pressures are by far the greatest pressure with reptiles, seabirds, marine mammals and shallow and littoral sediment being the most affected ecological components. The addition of already existing pressures, along with the appearance of new ones has led to changes in the pressures from certain already existing sectors.
Here, we make a comparison between the ODEMM of all sectors and each of the GTA phases (note that when we compare pressures or ecological components, the first number represents the position in all sectors and the second represents the position in the corresponding combination phase). We can see that:
The first combination, which included all existing sectors and construction phase, shows the influence of the GTA which occupies the 5th position. Some pressures caught our attention such as noise the main pressure which moved from position 8 to 3; siltation/smothering which moved from position 9 to 8; non-living resources a pressure specific to GTA project at position 13 and barriers which moved from position 16 to 14. For the ecological components, the impact increased on shallow sediment which moved from position 13 to 11 and deep sea elasmobranch which moved from position 20 to 17.
The GTA project drops to the 7th position in the second combination (all sectors and exploitation phase) with some changes in pressures and ecological components. Noise moved from position 8 to 6, wave exposure moved from 17 to 13, barriers moved from 16 to 14 and invasive species moved from 18 to 16. We also noted that except for shipping, he GTA project produces the greatest quantity of contaminating compounds. For the ecological components, two changes were noted: littoral sediment moved from position 12 to 11 and deep sea elasmobranch moved from position 20 to 19.
In the third combination (all sectors and decommissioning phase), the GTA project rises again to occupy the 7th position with a major change for abrasion which moved from 5th to 4th position. Then we have noise which moved from position 8 to 6, siltation/smothering which moved from position 9 to 8, wave exposure moved from 17 to 13, barriers moved from 16 to 14. For the ecological components, two changes were noted: shallow sediment moved from position 13 to 11 and deep sea elasmobranch moved from position 20 to 18.
4 Discussion
The use of ODEMM approach as an IEA tool offers several advantages including the availability of code for data analysis and a body of literature explaining the steps to follow for proper implementation. It, however, presented some issues during in our particular experience. These included the misunderstanding of certain terms and disagreements regarding some definitions during our interviews (Pedreschi et al., 2019). Some experts criticized the evaluation or grading method, which they consider to be subjective (Pedreschi et al., 2023). In addition, in our case study, we had noted pressures that were not present in the list of pressures in ODEMM, such as flaring.
Before the gas sector, fishing (both industrial and artisanal), shipping and agriculture were the main sectors impacting the marine environment in the region. The arrival of the GTA introduced new pressures and increased existing ones, but it also caused a redistribution of pressures, particularly due to the establishment of an exclusion zone, which can have some positive collateral impacts.
The GTA project has several impacts on the ecological components. Noise is present throughout all phases of operation especially during the exploration phase (seismic research). In certain cases, it can be recorded up to 4 000 kilometers from the vessel (Nieukirk et al., 2012) due to the easy propagation of sound in water (Moore et al., 2012; Richardson et al., 2013). It is the highest pressure introduced by this sector in every phase, except during the operation phase, where it ranks second after contaminating compounds. Noise can cause various types of behavior disturbances depending on the species (). For marine mammals which are most affected, sound is crucial for their survival, for communication, feeding research and avoiding predators (; Moore et al., 2012). Depending on the distance from the noise source, this pressure can cause serious damage to their ears often leading to their indirect death. For other species (e.g., turtles, seabirds, fishes), noise affects behavior such as temporary or permanent displacement, changes in swimming direction (Patin, 2018) or startle reactions in certain fish.
Contaminating compounds, the greatest pressure during the exploitation phase, can accumulate in the organism of species () and can be dangerous depending on the quantity absorbed. Under the effect of currents and waves this can affect reefs located in the buffer zone of the pipelines as well as mangroves and estuaries near the area. Species living in or around the facilities will be more impacted.
Abrasion and siltation/smothering present during the construction and decommissioning phases can cause suffocation or displacement of species. Platforms in this sector attract with artificial light several species such as fish () and seabirds (; Reed et al., 1985; Tasker et al., 1986; Wiese et al., 2001) which have been shown to sometimes even be incinerated by flaring (; Ronconi et al., 2015; Wiese et al., 2001) or suffer injury or death due to disorientation or collision (; ) during the night. This artificial light as in the case of the FLNG hub can also cause disorientation in turtles returning to their nests on sandy beaches (Longcore and Rich, 2004).
At the well level (deep sea), we do not have data, but based on the available literature, several negative impacts can be expected. This area hosts various benthic ecosystems, with sponges being a representative example and during the construction phase, the release of contaminants from drilling waste, gas leaks, and spills may occur (Rana, 2008), and such pollution can lead to severe reductions in the organisms living in or around these habitats (; Olsgard and Gray, 1995). In addition to species-level impacts, several forms of seabed disturbance may also be observed (; ; Vad et al., 2018).
The new offshore gas sector competes for space with the other existing sectors. Fishing, which is the main activity in this region (), is the most affected in the GTA area (including precautionary zones) due to the loss of fishing zone and the attraction of certain species around the GTA facilities. These installations are generally located in areas of great importance for (artisanal) fishing (Patin, 2018) as it is the case with the FLNG hub, which is situated in a very productive zone for artisanal fishermen called the Diattara reef. The ban to fish around the facilities (exclusion zone with a radius of 500 meters; ) forces fishermen to travel farther than usual to fish, resulting in higher fuel consumption and a reduced catch rate. Women involved in fish processing saw their incomes decline. These combined effects on artisanal fishermen and women processors generate a negative economic impact for both Senegal and Mauritania and affect the livelihoods of local communities. The GTA project, by being partly responsible for the scarcity of fishery products, has also contributed to unemployment and could inevitably lead to the clandestine migration of the most affected people toward Europe (; ). After the end of this production, several installations will remain in place, posing a threat to the fishing and shipping sectors (Patin, 2018).
However, during the operation of this new sector, these installations will serve as artificial reefs (; Stachowitsch et al., 2002; Techera and Chandler, 2015; van Elden et al., 2019) for several species leading to a large concentration of fish around these facilities (; ; Love et al., 2005) which will be protected from fishing. Also at the end of the operation the installations can continue to function as artificial reefs if the rigs-to-reefs approach is used which involves transforming the facilities into artificial reefs instead of removing them and bringing them back to the coast () as seen in the Louisiana artificial reef program (LARP; ) or in the nearby Chinguetti oil field, discovered in 2001 offshore Mauritania at a depth of 800 meters (Smith et al., 2004). Here (Chinguetti), to reduce collision risk with large fishing trawlers, a buffer zone around the FPSO with radius of app 6 km was established. They also secured an agent from the coast guard present at all times on the platform and the pilot vessel (Prigent et al., 2005). Ten years later, ROV (Remotely operated Vehicle) images in the Tamxat-Banda mounds complex revelaed living Maderpora regrowth corresponding to a decade of improved surveillance in the area around the FPSO ().
Thanks to their facilities and exclusion zones, the offshore gas sector could help reduce the pressure on fishing in the concerned zone (van Elden et al., 2019). In addition, in the GTA, the buffer zone is ecologically justified because it protects sensitive habitats, such as cold-water coral reefs, and ensures the sustainability of fish stocks. Bilateral management has already been implemented: Senegal and Mauritania have deployed coast guards aboard surveillance vessels to monitor the buffer zone, preventing illegal and artisanal fishing and regulating vessel traffic that may pose environmental or safety risks.
5 Conclusion
Nature is under pressure from human activities, both on land and in the ocean. In recent years the expansion of the offshore gas sector in the sea home to highly sensitive and vital ecosystems has triggered the need for effective measures to protect the environment. Perceived as a driver of development, this sector can benefit the population but, in most cases, it has a negative impact on the ecological components and other sectors operating in or around the area of operation. The ODEMM approach allowed us to understand the interconnections among sectors, pressures and ecological components, identifying the greatest pressures, the most affected ecological components and the impact of this new sector on the existing ones. All this information will enable decision-makers to implement effective management strategies.
Beyond the implementation of various protection measures, new strategies are necessary to ensure effective ecosystem-based management (EBM). We first recommend ensuring real-time availability of meteorological conditions, in order to better protect infrastructures. Secondly, regular maintenance of wells and pipelines should be ensured, along with the capacity to respond swiftly and effectively to any gas leak. Most importantly, coordination between the two countries must be strengthened. With regard to fishing, particularly artisanal fisheries, we recommend expanding the buffer zone, as was done in Chinguetti, and negotiating shared fishing grounds across the Senegal-Mauritania border.
Dialogue between the government, the GTA operator, and representatives of the various sectors affected by the project would be beneficial for identifying the challenges encountered and the solutions implemented. Given that the GTA project is expected to end within 20 years, we recommend allocating a portion of the revenues to implement ecosystem-based management in the region that ensures the three pillars of environmental, economic and social sustainability.
Statements
Data availability statement
The original contributions presented in the study are publicly available, further inquiries can be directed to the corresponding author/s. The csv data have been deposited in the Digital.CSIC repository, details are available at Seck et al. (2026), GTA IEA (ODEMM) data, http://hdl.handle.net/10261/421665 (deposited 4 March 2026), https://doi.org/10.20350/digitalCSIC/18169.
Ethics statement
Ethical review and approval was not required for the study on human participants in accordance with the local legislation and institutional requirements. Written informed consent from the participants was not required to participate in this study in accordance with the national legislation and the institutional requirements.
Author contributions
MS: Methodology, Supervision, Writing – review & editing, Investigation, Conceptualization, Data curation, Writing – original draft, Formal analysis, Software. BM: Validation, Writing – review & editing. BB: Investigation, Validation, Writing – original draft. SK: Data curation, Investigation, Validation, Writing – original draft. ML: Conceptualization, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing.
Funding
The author(s) declared that financial support was received for this work and/or its publication. This work was supported by the WAGAS and Mission Atlantic projects and by AECID (Spanish cooperation). Data collection: in situ interviews and team workshops were supported by the WAGAS (Trade-offs assessment between the gas, fishing and conservation sectors off West Africa) project (Call: iCOOP23 (CSIC). Ref: COOPB23053). MS acknowledges financial support from the Mission Atlantic project (Call: H2020-BG-2019-2, topic: BG-08-2018-2019 - All Atlantic Ocean Research Alliance Flagship. Project ID: 862428). BM (Mauritania) and BB (Senegal) visited IEO in 2024 (6 months) and 2024-25 (9 months) respectively thanks to the AECID fellowship programme: Convocatoria de becas MEC-AECID para ciudadanos de países de América Latina, África y Asia, programa Africa-MED INVESTIGA.
Conflict of interest
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declared that generative AI was not used in the creation of this manuscript.
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Publisher’s note
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Supplementary material
The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/focsu.2026.1702958/full#supplementary-material
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Summary
Keywords
Greater Tortue Ahmeyim (GTA), integrated ecosystem assessment (IEA), ecosystem-based management (EBM), option for delivering ecosystem-based marine management (ODEMM), ecological components, artificial coral reefs
Citation
Seck MN, M'Bengue B, Baldé BS, Kloff S and Llope M (2026) Offshore gas in West Africa as a driver of change: an assessment of impacts and redistribution of pressures. Front. Ocean Sustain. 4:1702958. doi: 10.3389/focsu.2026.1702958
Received
10 September 2025
Revised
13 February 2026
Accepted
16 February 2026
Published
01 April 2026
Volume
4 - 2026
Edited by
Luminita Lazar, National Institute for Marine Research and Development Grigore Antipa (INCDM), Romania
Reviewed by
Erik Cordes, Temple University, United States
Egemen Aras, Bursa Technical University, Türkiye
Updates
Copyright
© 2026 Seck, M'Bengue, Baldé, Kloff and Llope.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Marcos Llope, marcos.llope@ieo.csic.es
Disclaimer
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.