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Article

Citizen Science on Maritime Traffic: Implications for European Eel Conservation

by
Lucía Rivas-Iglesias
1,
Eva Garcia-Vazquez
1,
Verónica Soto-López
2 and
Eduardo Dopico
3,*
1
Department of Functional Biology, University of Oviedo, C/Julián Clavería s/n, 33006 Oviedo, Spain
2
Department of Marine Science and Technology, University of Oviedo, Escuela Superior de Marina Civil, Campus de Gijón, C/Blanco de Garay s/n, 33203 Gijón, Spain
3
Department of Education Science, University of Oviedo, Campus Llamaquique, C/Aniceto sela s/n, 33505 Oviedo, Spain
*
Author to whom correspondence should be addressed.
Oceans 2025, 6(3), 50; https://doi.org/10.3390/oceans6030050
Submission received: 5 March 2025 / Revised: 14 July 2025 / Accepted: 31 July 2025 / Published: 13 August 2025
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Abstract

Maritime traffic accounts for more than 90% of world trade. Noise, pollution, and litter are its drawbacks, affecting especially vulnerable migratory fish. Here, a motivated team of citizen scientists analyzed maritime traffic from three estuaries of the south Bay of Biscay and three from the south of the Iberian Peninsula, where the European eel is critically endangered, during the season of the entrance of glass eels. More than 164,000 data points about ship types and positions were collected. The results showed that traffic differences between estuaries would explain, at least partially, the different eel conservation statuses. The participants appreciated learning about ships and nature conservation and acquiring an awareness of the real volume of shipping and its potential impacts. All the citizen scientists, new and experienced, would like to get involved in ocean research again.

1. Introduction

Maritime transport represents the principal means of international trade, with approximately 80% of the world’s goods transported by sea. The United Nations Conference on Trade and Development [1] has estimated the size of the world’s merchant fleet. Global maritime trade was transported on board 105,493 vessels of 100 gross tons (GT) and above in January 2023, with oil tankers, bulk carriers, and container ships accounting for 85% of the total capacity. The global shipping sector currently moves approximately 11 billion tonnes of cargo annually, with projections indicating a minimum increase of 240% by 2050 [2]. Despite the predominance of maritime transport in terms of its significance in maintaining global supply chains and its economic value within the nautical sector, a significant yet often disregarded component of this domain warrants attention: namely, smaller vessels. These vessels are defined as those with a length of less than 24 m (78.74 feet) and a 50-tonne internal volume measured in GT. The importance of these vessels lies both in their number, which is estimated to be 28,000,000 worldwide, and in their role in nearshore activities [3]. However, despite their abundance, smaller vessels are often underrepresented in global shipping assessments due to limited data availability. This expansion of maritime traffic can also give rise to concerns regarding pollution, safety, and marine conservation due to the environmental impact caused by the discharge of water used to stabilize ships, which often contains elevated levels of heavy metals such as mercury, lead, and cadmium. Proper ballast water management helps maintain the health of marine ecosystems [4]. On the other hand, fuel spills are considered to have a significant impact as they consist mainly of sulfur compounds, alkylphenols, and heavy metals [5].
Shipping has significant impacts on marine fish species. To give a few examples, the presence and movement of vessels changes the home range of Arctic cod compared with periods without maritime traffic [6]. In estuaries, boat movements cause a decrease in the abundance of mid-sized fish, attributable to the noise and the production of bubbles [7]. Motorboat traffic significantly reduces the call rate of different fish species, altering the complexity of the fish assemblages [8]. Likewise, commercial shipping negatively affects the communication of both Atlantic cod and haddock [9].
The European eel, Anguilla anguilla, has experienced a drastic reduction in its populations since the last decades of the 20th century and has been cataloged as a critically endangered species by the International Union for Conservation of Nature since 2008 [10,11,12]. This species is catadromous, which means that they reproduce in the ocean and migrate to grow in freshwater [13]. The European eel spawns in the Sargasso Sea and grows in European and North African continental waters (Figure 1).
The leptocephalus larvae, which are the early developmental stages of the eel (Figure 2), travel from the Sargasso Sea to the coasts of Europe and North Africa, enter the river estuaries, and run upstream [15,16]. They arrive in the estuaries in the second development stage, as transparent juveniles called glass eels. When juveniles enter the river and start running upstream, they acquire pigmentation and are called elvers. In the river, they settle as yellow eels (immature adult phase). After 5 to 25 years growing in continental waters, they start a silvering process, and as silver eels they migrate downstream and travel back to the Sargasso Sea to reproduce [17,18,19,20].
Perhaps the most vulnerable stage of A. anguilla is the glass eel phase, in which they face many stressors when arriving in the estuaries. There, they are exposed to an abrupt natural change in salinity, to a new ecosystem with parasites and predators, and to anthropogenic disturbances like river pollution, fishing, and shipping [21,22]. The status of the European eel differs across its distribution in European waters, depending on the particular region and the natural and anthropogenic disturbances they find therein. On the Iberian Peninsula, there is a difference between the north and the south coasts. In the north (south Bay of Biscay, Cantabrian Sea, Galicia) the populations are still fished when entering the rivers, although the exploitation of yellow and silver eels is forbidden [23]. In contrast, in the south, the species is in a very bad situation and its fishing has been banned in Andalusia since 2010. Overfishing was considered one of the main causes of the 98% decline in eel populations, as well as the reduction in eel habitats of 88% [24]. In response, the Regional Government of Andalusia adopted a 10-year moratorium on eel fishing, including the ban on the capture of all stages of European eel, both in inland and continental maritime waters, to recover the species. These measures were in addition to the Eel Management Plan of Andalusia, which consisted mainly of the prohibition of harvesting, but also the protection against predators, the transport of eels from inland waters to the sea, and their restocking through aquaculture. However, by 2020, the eel population had not yet recovered sufficiently to resume fishing, and the ban was extended for another decade [25]. But, for the protection and maintenance of the species, prohibition is not the only suitable measure. Fishery management and conservation requires taking into account not only the fish and their habitat, but also the people [26], from the fishermen associated with the resource [27] to the stakeholders interested in it. In this way, successful collaborative initiatives can be developed [28].
Maritime transport may contribute to the difference in the A. anguilla conservation status between European regions, not only because of the known pollution caused by vessels [29] but also because this species is sensitive to boat noises [30]. Large and medium estuaries shelter maritime ports whose increasing activity surely interferes with European eels during their most vulnerable stage, when they are about to experience the change from glass eels to elvers and must adapt to freshwater [31]. In the rivers of the north and south of the Iberian Peninsula, the entrance of glass eels occurs between the end of autumn and the end of winter, especially in a time window between December and February. During that window, dense maritime traffic could impact this critically endangered species in its most vulnerable stage as fragile glass eels. To monitor maritime traffic, we launched a citizen science strategy [32], that is, encouraging citizen participation in the gestation and development of a scientific project. Citizen involvement is essential, as it allows for a much broader record of data that would otherwise be difficult to obtain. This approach not only enhances scientific research but also environmental awareness and engagement among participants, strengthening the connection between society and marine conservation efforts.
Our study therefore focused on two main objectives: to determine whether maritime traffic could affect glass eels when they enter the estuaries in the north and south of the Iberian Peninsula (December to February run window), and if citizen science could be a good research resource to verify it. While we explore the possible links between vessel presence and eel conservation status, our primary aim is to showcase citizen science as an effective tool to monitor anthropogenic pressures in estuarine environments. On one hand, as the European eel is more affected in the south, we expected to find more intense traffic in southern estuaries during the season of the entrance of glass eels. On the other hand, we hope that the direct involvement in research of the recruited people will motivate them to get involved in new citizen science initiatives.

2. Materials and Methods

2.1. Ethics Statement

In accordance with the ethical principles of scientific research [33], non-discriminatory and culturally respectful procedures were followed in recruiting volunteers who later became citizen scientists. Likewise, this research has followed the European Code of Conduct for Ethical and Responsible Research [34], as well as Regulation (EU) 2016/679 of the European Parliament and of the Council, of 27 April 2016, regarding the protection of natural persons with regard to the processing of personal data. All participating citizens were informed in detail about the objective of this study, agreed to participate voluntarily without any financial compensation, and are aware of the results obtained.

2.2. Citizen Science Recruitment

The volunteers were recruited using the snowball methodology [35], starting in the Faculty of Biology and the Higher School of Civil Navy of the University of Oviedo. Our students, by and large, met the basic criteria of the study we intended to carry out (time and desire) and so we invited them to become volunteers while suggesting the recommendation of other possible participants who also met these criteria. Having been turned into citizen scientists [36], 21 participating volunteers aged between 23 and 66 years were trained to visualize maritime traffic online on the website https://www.marinetraffic.com [37] (accessed on 12 June 2024) and received instructions in writing about how to use the webpage and register data. They were also asked to take screenshots from that online application showing the number and type of vessels present during their records, and additional information to validate the recorded information if needed.

2.3. Estuaries Studied

Six estuaries were investigated in this study: those of the Nalón and the Sella rivers and the estuary of Avilés, in the region of Asturias in the Cantabrian coast, and those of the Odelouca (Algarve region), Guadiana, and Guadalhorce rivers (Andalusia region), in the south of the Iberian Peninsula (Figure 3). The main characteristics of each estuary are summarized in Table 1.
The status of the European eel in the two regions was estimated from the official data of the national management plan of A. anguilla in Spain [39]. The wetland area for the European eel in each region (pristine, as pre-industrial, and currently available), the estimated pristine escapement of the eels allowed to escape the fishery and spawn, and the current escapement are the variables displayed in the management plan. The details for the calculations of escapement are given in the management plan and correspond to the report of the EIFAC/ICES working group on eels [40]. The details of the rivers are not available for all the studied rivers.

2.4. Maritime Traffic Records

The protocol consisted of collecting data from the Maritime Traffic website mentioned above. It is a website that shows the real-time tracking of ships around the world and allows you to choose a region on the world map and observe all of the maritime traffic that occurs in a time interval and the type of ships that are sailing in that specific area. The website takes information from the Automatic Identification System (AIS), which is used in maritime navigation for the automatic exchange of information between different vessels or between vessels and land stations. It allows ships to transmit data such as their position, speed, heading, course, and other relevant details, using radio frequency signals. Since 31 May 2014, all fishing vessels over 15 m in length operating within the EU must be equipped with AIS. More information about this system can be found from the International Maritime Organization [41]. However, it is important to highlight that not all vessels are required to carry AIS transmitters. In particular, smaller vessels, such as recreational boats and artisanal fishing vessels under 15 m, are not equipped with AIS and therefore are not captured in this dataset. This limitation should be considered when interpreting the results derived from AIS-based maritime traffic data.
The project lasted from December to February to cover the main period of the entrance of glass eels into the studied rivers. The volunteers checked the webpage four times a day (8:00 AM, 12:00 PM, 16:00 PM, and 20:00 PM) and collected data about the number and type of vessels, among others. The citizen scientists were organized to register data on times and days compatible with their availability and preferences. The data were recorded in spreadsheets for further analysis.

2.5. Post-Activity Survey

After the observation period, the citizen scientists were asked to answer an online questionnaire with the following three questions (the first as a Likert scale question and the next two as dichotomous questions):
(1)
Between 0 as extremely bad and 10 as extremely good, how do you evaluate this citizen science experience?
(2)
Could you please describe briefly what was the most interesting part of this project for you?
(3)
After this experience, would you participate in other citizen science projects? (yes/no)
Socio-demographic data (age group as >30 or <30 years old; gender as woman, man, or non-binary; and education level as the highest degree earned) were also gathered.

2.6. Data Curation

The data in the spreadsheets were examined by the researchers and the format was homogenized whenever necessary (for example using the same system, comma or period, for decimal positions, etc.). In some cases, the names of the vessels monitored by citizen scientists were written in capital letters, and others were written in lowercase, or their descriptions did not exactly correspond to their real names. Furthermore, since there are many types of vessels, it was decided to unify their description by type (Table 2) to facilitate the use of the data.
During vessel monitoring and tracking, when a vessel did not move during the data collection time (4 h) it was counted only once for the final count.

2.7. Statistics

For quantitative data like the scores given by citizen scientists to the experience, first, the dataset normality was checked using the Shapiro–Wilk test. Since it was not met, non-parametric PERMANOVA tests with 9999 permutations and the Bray–Curtis distance were employed to compare the groups of participants (e.g., men versus women, secondary versus higher education, people over 30 years old versus people under 30 years old).
For qualitative data, such as the proportion of different types of vessels, a comparison between the north and south of the Iberian Peninsula was performed using contingency analysis. The quantitative comparison between the north and south regions for the maritime traffic was performed from the numbers of vessels in each estuary using an unpaired (independent) two-sample Student’s t-test, assuming unequal variances. The null hypothesis (H0) was that there is no difference in vessel numbers between the northern and southern estuaries; the alternative hypothesis (H1) was that there is a significant difference between the two regions. The comparison between the north and the south for the reduction in the European eel was based on the proportion of current versus pristine escapement in each region. The comparison was made with a z-test. The null hypothesis was that there is no difference in escapement reduction between the two regions. A p-value below 0.05 was considered statistically significant for all tests. Statistics were performed using the PAST free software version 4.17 [42].

3. Results

3.1. Citizen Science Performance and Volunteer Satisfaction

The 21 volunteers collected a total of 33.887 data points from the Bay of Biscay and 130.644 data points from the Mediterranean Sea, which were recorded daily from the 8 December 2023 to the 15 February 2024. There were no failures to monitor maritime traffic, and records were made even during weekends and the Christmas holidays.
The volunteers considered the activity satisfactory because the mean score was 8.36 (SD = 1.14 (Figure 4)). However, there were some observable differences between the groups of participants, e.g., men versus women, or individuals with higher education versus those of lower educational levels. The data did not meet normality, thus a non-parametric PERMANOVA test was employed. No significant effect of gender (F = 2.63, p = 0.124) or age (F = 0.358, p = 0.532) was found. In contrast, individuals of higher education scored the experience significantly higher than the rest (mean 8.59 with SD 0.93 versus 7.6 with SD 1.5, respectively; F = 3.975, p = 0.043).

3.2. Maritime Traffic Recorded in the Studied Estuaries

All of the information was taken from the webpage of Marine Traffic, such as the type, origin, destination, and course of each vessel, among others. The raw data collected [43] is part of a larger ongoing investigation. Maritime traffic was more intense in the south than in the north during the studied period (Figure 5), with a total of 3962 ships in the three estuaries of the Bay of Biscay (2521, 600, and 841 for the Avilés, Nalón and, Sella estuaries, respectively) and 11,256 in those of the south of the Iberian Peninsula (3002, 4452, and 3802 for the Guadalhorce, Guadiana, and Odelouca estuaries, respectively). The difference between the north and the south for the number of vessels per estuary was significant (t = 3.306, p = 0.029).
The types of vessels were also quite different (Table 3), with cargo being more abundant in the north and recreational and passenger vessels in the south. The difference between the two Iberian coasts (north versus south) was highly significant (Chi-square = 1693.4, 4 d.f., p < 0.001).
The state of the European eel in the two regions considered is summarized in Table 4. The reduction in eel escapement has been much more drastic in Andalusia than in Asturias, where the relative situation of the species is better, with around 37% of remaining escapement versus only 17% in Andalusia. The reduction in the species, using this proportion of current escapement versus the escapement estimated in pristine conditions as a proxy, was indeed significantly greater in the south than in the north (z = 84.65, p < 0.001).
The cumulative pressure of maritime traffic is illustrated in Figure 6, representing the vessel density across the estuaries during the period studied. The highest pressures are concentrated in routes passing through the Gulf of Gibraltar, aligning with the estuaries that also exhibit a higher proportion of commercial and fishing vessels.

4. Discussion

Although in the research activity developed, the participants with a higher educational level rated the experience significantly better than those with a lower level, we share the idea that the active participation of citizens in scientific activities contributes to the population’s scientific literacy [44]. It also serves to democratize science, making it accessible to everyone. The group of volunteers who turned into citizen scientists showed their satisfaction in carrying out this study. Having highly motivated citizens concerned about the protection of ecosystems and the desire to contribute to minimizing global change [45] helps to develop scientific projects from new perspectives [46,47]. Citizen science strategies also play an active and valid role in research on marine ecosystems [48]. Here, in the observation and monitoring of maritime traffic and the impact it causes on migratory aquatic species, specifically on the European eel, the contributions of the participating citizen scientists have been a key element in the approach, development, and results of the research. The value of citizen science strategies has already been significantly accredited [49,50,51], so we support the convenience of including citizens in scientific research whenever possible.
In this study, data was extracted from the Maritime Traffic website, which provides real-time AIS data. However, the results are based on discrete snapshots taken at four fixed times daily and specific sampling points, rather than continuous fine-scale AIS tracking. This sampling approach allowed manageable data collection through citizen science, though it does not capture the full temporal resolution of vessel movements.
The landscape of estuary maritime traffic revealed from the citizen science strategy developed in this study is very different in the north and the south of the Iberian Peninsula. In the south, the number of recorded vessels during the entrance of fragile glass eels in the estuaries was three times higher than in the north. This coincides with a worse conservation status of migratory European eels in the south measured by the respective reduction in eel escapement, which could be due, at least partially, to the impacts produced by the boat movements. The sensitivity of the species to the sound of ship engines while sailing would support this possibility, as eels exposed to ship noise alter their swimming and predator avoidance behaviors [52]. Other reasons may be ship-derived pollution like oil and chemical spills, antifoulants, garbage, sewage, and more [53], because the species is very sensitive to pollution [54].
What is evident is that migratory fish are especially affected by maritime traffic, which can alter not only their habitats but also the behavior of their species [55]. Noise pollution has been shown to alter the orientation and communication of species that use acoustic signals to navigate, feed, and avoid predators [56,57]. In areas with high densities of shipping, such as the Mediterranean Sea, migratory fish can suffer from collisions, especially in coastal areas and estuarine zones, where fish usually spend long periods of time during their life cycle [58,59]. Many studies have been conducted to monitor and estimate the impact of ship collisions with whale species [60], such as the case of the fin whale in the Mediterranean Sea [61]. Oil and chemical spills left by vessels produce toxic effects in the marine environment, affecting every living organism in the impacted area [62]. Coastal structures [63], harbor facilities, channels, and barriers are sources of pollution, but they can also act as obstacles for migratory routes [64]. The European eel depends on the connectivity between freshwater and marine ecosystems, and such interruptions may alter its life cycle [65,66]. Coastal areas and estuaries, used as spawning sites for migratory species, can be degraded or even destroyed during the construction of ports and dredges [67]. Finally, shipping activities are sources for the introduction of invasive species through ballast water, leading to modifications of the habitat and competition with the local marine species for habitat and food [68,69,70]. From these results, we can recommend some management measures to help the critically endangered European eel. Establishing corridors free of marine traffic in the estuaries could be proposed, especially in the south, where the pressure of maritime traffic is much higher. The corridors could be established during the migration season of glass eels to protect the species in this vulnerable stage.
Finally, this study was focused on the European eel because it is critically endangered, thus we have chosen its season of arrival in the estuaries from the sea as the time window for the analysis. Indeed, many other migratory species could benefit from the establishment of corridors during migration seasons, in any direction (river–sea or sea–river, as in this case). Examples of important migratory fish in the studied regions could be the threatened sea lamprey (Petromyzon marinus) in both regions, the vulnerable anadromous Atlantic salmon (Salmo salar L.) in the north, and the critically endangered European sea sturgeon (Acipenser sturio) in the south.

5. Conclusions

This study highlights the role of citizen science in monitoring maritime traffic and its potential impact on migratory fishes, particularly the European eel, known for its long migration route. Our findings reveal significant differences in maritime traffic between the north and south of the Iberian Peninsula, with a higher vessel volume in the south, coinciding with a worse conservation status of the European eel. Maritime traffic produces noise pollution, habitat disruption, ship-derived contaminants, and physical barriers for migratory fishes. Given these impacts, we recommend the establishment of marine traffic-free corridors in estuaries during the migration season of glass eels to support conservation efforts given its critical status.
More broadly, this study illustrates how citizen science can serve as an effective approach to detect and monitor anthropogenic pressures in estuarine ecosystems. By engaging local communities in systematic observations, we were able to gather valuable spatiotemporal data that can support future research. While we used the case of the European eel as a focal point, the methodology presented here can be applied to other conservation and environmental monitoring challenges. Future research should focus on directly studying the biological responses of eels to maritime traffic, such as behavioral changes, physiological stress, and long-term population impacts.

Author Contributions

Conceptualization, L.R.-I., V.S.-L. and E.G.-V.; methodology, L.R.-I., V.S.-L., E.G.-V. and E.D.; software, L.R.-I. and V.S.-L.; validation, E.G.-V. and V.S.-L.; formal analysis, L.R.-I., V.S.-L. and E.G.-V.; investigation, L.R.-I., V.S.-L., E.G.-V. and E.D.; resources, E.G.-V. and V.S.-L.; data curation, L.R.-I., V.S.-L. and E.G.-V.; writing—original draft preparation, L.R.-I., V.S.-L., E.G.-V. and E.D.; writing—review and editing, L.R.-I., V.S.-L., E.G.-V. and E.D.; visualization, L.R.-I., V.S.-L., E.G.-V. and E.D.; supervision, E.G.-V. and V.S.-L.; project administration, E.G.-V. and V.S.-L.; funding acquisition, E.G.-V. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Spanish Ministry of Science, Innovation and Universities Grants PID2022-138523OB-100 and FCT-23-19037, and by the Government of Asturias region Grant GRU-GIC-24-051.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study. Also, written informed consent was obtained from the individuals cited for publication of this article.

Data Availability Statement

The raw data are available in the public EUDAT repository with the DOI https://doi.org/10.23728/b2share.8d8f33e4fcb640abb2269ec61ad7213c (accessed 29 October 2024).

Acknowledgments

Special thanks to the volunteers who enthusiastically and kindly wished to become citizen scientists and participate in this research project. We also express our gratitude to Aida Dopico Garcia for the review and editing of the entire manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Map with the route followed by Anguilla anguilla that grows in Iberian rivers, showing the spawning site (Sargasso Sea), the maritime traffic occurring on 24 May 2024, and the migration route the species follows between Iberian rivers and the Sargasso Sea (blue arrows). This self-made map has been generated from the website https://globalmaritimetraffic.org/ [14] (accessed on 11 August 2024).
Figure 1. Map with the route followed by Anguilla anguilla that grows in Iberian rivers, showing the spawning site (Sargasso Sea), the maritime traffic occurring on 24 May 2024, and the migration route the species follows between Iberian rivers and the Sargasso Sea (blue arrows). This self-made map has been generated from the website https://globalmaritimetraffic.org/ [14] (accessed on 11 August 2024).
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Figure 2. Life cycle of the European eel Anguilla anguilla.
Figure 2. Life cycle of the European eel Anguilla anguilla.
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Figure 3. Map with the locations of the six estuaries analyzed: those of the Nalón and the Sella rivers and the estuary of Avilés, in the region of Asturias, Spain, and those of the Odelouca, in Portugal, Guadiana, on the Portugal–Spain border, and Guadalhorce rivers, in Málaga, Spain (Andalusia region). This self-made map has been generated from the website https://earth.google.es/ [38] (accessed on 23 January 2025).
Figure 3. Map with the locations of the six estuaries analyzed: those of the Nalón and the Sella rivers and the estuary of Avilés, in the region of Asturias, Spain, and those of the Odelouca, in Portugal, Guadiana, on the Portugal–Spain border, and Guadalhorce rivers, in Málaga, Spain (Andalusia region). This self-made map has been generated from the website https://earth.google.es/ [38] (accessed on 23 January 2025).
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Figure 4. Evaluation of the citizen science experience by the participants, with a mean score (SD as capped bars) over a maximum of 10 as extremely good. Data are presented by age, gender, and education level.
Figure 4. Evaluation of the citizen science experience by the participants, with a mean score (SD as capped bars) over a maximum of 10 as extremely good. Data are presented by age, gender, and education level.
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Figure 5. Proportion of types of vessels (cargo, fishing, special craft and sailing, passengers, and naval craft) for the studied estuaries. The difference in sizes of the graphs responds to the abundance of maritime traffic per estuary.
Figure 5. Proportion of types of vessels (cargo, fishing, special craft and sailing, passengers, and naval craft) for the studied estuaries. The difference in sizes of the graphs responds to the abundance of maritime traffic per estuary.
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Figure 6. Cumulative pressure scores of the maritime traffic in the Iberian Peninsula during December (a), January (b), and February (c). The color scale ranges from blue (low pressure) to red (high pressure). The values range from 0 to 100+, representing relative cumulative pressure scores. This map has been generated from the website https://globalmaritimetraffic.org/ [14] (accessed on 11 August 2024).
Figure 6. Cumulative pressure scores of the maritime traffic in the Iberian Peninsula during December (a), January (b), and February (c). The color scale ranges from blue (low pressure) to red (high pressure). The values range from 0 to 100+, representing relative cumulative pressure scores. This map has been generated from the website https://globalmaritimetraffic.org/ [14] (accessed on 11 August 2024).
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Table 1. Estuaries considered. The location coordinates, river length, and number and type of ports (commercial, fishing, marina) are provided.
Table 1. Estuaries considered. The location coordinates, river length, and number and type of ports (commercial, fishing, marina) are provided.
EstuaryCoordinatesRiver Length (km)Number and Type of Ports
Nalón43°33′53″ N
006°04′36″ W		140.8Two fishing ports
Sella43°28′02″ N
005°03′51″ W		66A fishing port and a marina
Ria of Avilés43°35′34″ N
005°56′08″ W		22.1A fishing port and a marina
Odelouca37°10′38″ N
008°29′07″ W		92.5A marina
Guadiana39°07′54″ N
003°43′59″ W		865Two fishing ports and three marina ports
Guadalhorce36°39′58″ N
004°27′18″ W		154A fishing, commercial, and marina port
Table 2. Types of vessels and their nomenclature.
Table 2. Types of vessels and their nomenclature.
NomenclatureVessel Type
Bull carrier; Oil/Chemical tanker; Container; Crude oil tanker; LPG tanker; Ro-Ro/Passenger ship; General cargo; Cargo vessel; Chemical vessel; Container cargo; Container ship; Container vessel; Vehicles carrierMEs (Merchant vessels)
Trawler; Fishing; Fishing vesselFIs (Fishing vessels)
Special craft; Sailing vessel; Recreational craft; Yacht; Firefighting vessel; SARSCs (Special Craft vessels)
PassengerPAs (Passenger vessels)
Naval craft; Maritime opsNCs (Naval vessels)
Table 3. Proportion of different vessel types in each Iberian coast examined. N, total number of vessels recorded.
Table 3. Proportion of different vessel types in each Iberian coast examined. N, total number of vessels recorded.
Iberian CoastType of Vessel
SouthNorth
0.0540.255Cargo
0.3040.136Fishing boat
0.5790.609Special craft + sailing + recreational
0.0580Passenger vessel
0.0060Naval craft
11,2563962N
Table 4. State of the European eel in the studied regions. Wetland area, pristine escapement, and current escapement of A. anguilla in Asturias and Andalusia. The escapement percentage (current versus pristine) is indicated. Data was taken from the Spanish management plan of European eel (Government of Spain).
Table 4. State of the European eel in the studied regions. Wetland area, pristine escapement, and current escapement of A. anguilla in Asturias and Andalusia. The escapement percentage (current versus pristine) is indicated. Data was taken from the Spanish management plan of European eel (Government of Spain).
AndalusiaAsturias
Wetland area, pristine (ha)186,757.02306.6
Wetland area, current (ha)61,335.01635.1
Pristine escapement (kg)3,735,14046,132.2
Current escapement (kg)626,15016,513.3
Current/pristine escapement (%)16.8%35.8%
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Rivas-Iglesias, L.; Garcia-Vazquez, E.; Soto-López, V.; Dopico, E. Citizen Science on Maritime Traffic: Implications for European Eel Conservation. Oceans 2025, 6, 50. https://doi.org/10.3390/oceans6030050

AMA Style

Rivas-Iglesias L, Garcia-Vazquez E, Soto-López V, Dopico E. Citizen Science on Maritime Traffic: Implications for European Eel Conservation. Oceans. 2025; 6(3):50. https://doi.org/10.3390/oceans6030050

Chicago/Turabian Style

Rivas-Iglesias, Lucía, Eva Garcia-Vazquez, Verónica Soto-López, and Eduardo Dopico. 2025. "Citizen Science on Maritime Traffic: Implications for European Eel Conservation" Oceans 6, no. 3: 50. https://doi.org/10.3390/oceans6030050

APA Style

Rivas-Iglesias, L., Garcia-Vazquez, E., Soto-López, V., & Dopico, E. (2025). Citizen Science on Maritime Traffic: Implications for European Eel Conservation. Oceans, 6(3), 50. https://doi.org/10.3390/oceans6030050

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