Research

INTRODUCTION

The Mediterranean Sea is threatened by a variety of human-related stressors (Halpern et al. 2008, 2015). These include pollution and nutrient loads (Piroddi et al. 2017), habitat and biodiversity loss (Coll et al. 2016), the introduction of invasive species (Galil et al. 2014), and climate change (Lejeusne et al. 2010, Zittis et al. 2019). According to the FAO (2020), unsustainable overfishing also significantly impacts the Mediterranean Sea. The decline in fish stocks is alarming. The effects are strongly felt across the dependent socioeconomic sectors, such as the small-scale fishery (SSF) sector, which accounts for 80% of the Mediterranean fishing fleet (Said et al. 2018, FAO 2020). Small-scale fisheries are defined as those “traditional fisheries involving fishing households (as opposed to commercial companies), using relatively small amounts of capital and energy, relatively small fishing vessels (if any), making short fishing trips, close to shore, mainly for local consumption,” and represent an iconic example of the intricate links between people and nature (FAOTEDTER 2007–2016, as cited in Thiault et al. 2017).

In Spain, the SSF sector constitutes an important segment of the national fishing fleet and holds considerable historical, cultural, economic, and social value (Pascual-Fernández et al. 2020). Spanish Mediterranean fishing is a multi-species fishery involving nearly 29% of the Spanish national fleet and is focused on fish of high commercial value. Over 55% of vessels in this fleet are small-scale (< 12 m length), and the most common gear are trammel nets, long lines, and gill nets (Herrera-Racionero et al. 2019, Pascual-Fernández et al. 2020). Nonetheless, SSF in this country faces a diversity of challenges. This sector not only remains susceptible to the historical and ongoing pressures that impact the Mediterranean basin but also grapples with economic globalization and intense competition from large-scale fishing fleets and recreational fisheries (Pascual-Fernández et al. 2020). Urban development and tourism also affect coastal and harbor areas, thereby influencing marine ecological processes and potentially encroaching upon areas that were predominantly utilized by SSF in the past (Pascual-Fernández et al. 2020).

Among the Spanish regions bordering the Mediterranean, Catalonia holds a prominent position in terms of its significance within the SSF sector. In this region, SSF represents a substantial economic industry (Pascual-Fernández et al. 2020) and embraces important traditional and cultural heritage (Carbonell 2014). Particularly, Barcelona, the main city of Catalonia, has a robust fishing tradition and currently serves as a pivotal socioeconomic sector not only for the city but also for the wider Catalan region and the nation of Spain (Carbonell 2014). However, following the heavy industrialization processes and environmental deterioration during the first decades of the 21st century, the SSF sector of Barcelona has undergone rapid alteration and an overall decrease in the number of SSF vessels and active fishers. This was mainly due to a more competitive relationship with more industrialized and technologically advanced vessels (e.g., bottom trawlers and purse seines) and recreational fishermen with significant repercussions on certain species of fish and the marine environment (Peñuelas et al. 2021). As a result, the SSF sector in this region has experienced a continuous decline since the 1980s up to the present day, facing a profound crisis that poses a serious risk of eroding the local maritime heritage (Carbonell 2014, Pascual-Fernández et al. 2020). The need for management and conservation strategies that account for social-ecological processes is increasingly evident (Berkes et al. 2000, 2003). Local ecological knowledge (LEK), also referred to as indigenous and traditional ecological knowledge (IEK or TEK), is gaining recognition as a crucial complementary source of information. LEK encompasses knowledge, practices, and beliefs about ecological relationships developed through extensive personal observation and interaction with local ecosystems, which are then shared among resource users (Charnley et al. 2007). Its integration into management frameworks is essential for effectively preserving ecosystem services and biodiversity (Aswani et al. 2018, Evangelista et al. 2024). Although a hybrid approach that combines scientific and local ecological knowledge is generally recommended, it becomes even more critical in contexts where scientific data are limited (Huntington 2000).

When it comes to fisheries, for example, the Mediterranean Sea is classified as a “data-poor” region because of its limited number of empirically assessed stocks and the little biological (i.e., fishery-independent) data available (Payne et al. 2008, Demirel et al. 2020), limiting our understanding of ecological trends (Daw 2010). This limitation highlights the importance of incorporating alternative sources of knowledge, such as local ecological knowledge (Leitao et al. 2020). Fishers have been an additional source of information in scientific research because they have a broad knowledge of a range of ecological and biological aspects of the resources they exploit (Silvano et al. 2006, Silvano and Valbo-Jørgensen 2008, Coll et al. 2014, Leitao et al. 2020). Recent studies show how fishers’ ecological knowledge (FEK) has played a central role in the assessment of past environmental conditions, including historical baselines (McQuatters-Gollop et al. 2019, Pita et al. 2020), long-term changes in marine ecosystems’ structure (Viegas et al. 2016), fish catches (Fortibuoni et al. 2010, Beaudreau and Levin 2014, Coll et al. 2014, Martins et al. 2018), benthic diversity (Azzurro et al. 2011, Bastari et al. 2017), and species’ ecology and behavior (Gaspare et al. 2015, Veneroni and Fernandes 2021), providing evidence of their understanding of biological and ecological characteristics and trends in marine ecosystems (Thurstan et al. 2016, Sáenz-Arroyo and Revollo-Fernández 2016). Furthermore, an increasing body of research examining the incorporation of FEK into the management of fisheries indicates that fishers can provide reliable insights regarding the processes of fisheries management (Silvano et al. 2006, Zukowski et al. 2011). Notably, in some cases, the utilization of FEK has led fishers to actively participate in conservation initiatives and decision-making processes, thereby enhancing their societal and political role (Shackeroff and Campbell 2007, Veneroni and Fernandes 2021).

Nevertheless, the use of FEK for scientific purposes implies the consideration of psychological issues, including memory biases and altered perceptions (Daw 2010), as well as diverse beliefs related to historical and present environmental conditions, which may reflect cross-generational gaps (Zapelini et al. 2020). FEK can therefore be affected by the so-called “shifting baseline syndrome” (SBS), defined as a psychological and sociological phenomenon under which the perception of “normal” environmental conditions is slowly but persistently downgrading with time (Pauly 1995, Fortibuoni et al. 2017, Soga and Gaston 2018, Jones et al. 2020). This phenomenon is growing among the fishing community worldwide (Giglio et al. 2015, Ulman and Pauly 2016).

As a psycho-social phenomenon, SBS is not limited to fisherfolk or local community members but occurs among researchers and policy makers. This manifests when they perceive less change because they are not aware of, fail to recall accurately, or have not known because of intergenerational changes what the environment was like in the past (Soga and Gaston 2018). Therefore, SBS can be observed among fishery or marine scientists who accept the stock size, species composition, or coral cover percentage existing at the commencement of their careers as the standard baseline, as exposed by Pauly in 1995 and more recently examined by Muldrow et al. (2020). The two mechanisms by which SBS occurs are (1) generational amnesia, or (2) personal amnesia (Jones et al. 2020). Generational amnesia refers to the unperceived loss of knowledge between generations. It occurs because of a lack of intergenerational communication, which prevents an accurate perception of current and past conditions (Kahn and Friedman 1995). Personal amnesia pertains to individuals who possess an accurate perception of current circumstances but cannot recall previous conditions. As a result, individuals tend to recall past circumstances as if they were comparable to current ones (Papworth et al. 2009). Conversely, there may exist a tendency to remember past situations more vividly than recent ones (Simons and Rensink 2005). Hence, before employing FEK to complement or foster scientific knowledge, it is advisable to conduct an assessment to determine the occurrence of SBS. This way, it becomes feasible to ascertain whether the local community’s perception of past and present environmental conditions is accurate or distorted by time and/or by generational differences.

To empirically assess the presence of SBS two criteria are to be met: (1) biological changes must be present in the system and (2) perceived changes must be consistent with biological data (Papworth et al. 2009, Ulman and Pauly 2016, Guerrero-Gatica et al. 2019). In the context of fisheries, a growing number of studies have assessed the occurrence of SBS among fishers in various regions across the world (Giglio et al. 2015, Fortibuoni et al. 2016, Ulman and Pauly 2016). These studies emphasize the importance of employing participatory approaches for continued data gathering and the construction of management measures in conjunction with the fishers. In the Spanish context, recent studies conducted in the fishery community in Murcia (SW Mediterranean), found no evidence of SBS, suggesting that fishers’ perceptions could serve as valuable information both for the study of social-ecological system dynamics and for the empowerment of communities (Leitao et al. 2020). Although previous works in the Catalonia region focused on the role of maritime heritage in implementing adaptive measures along the north coast of Barcelona (Carbonell 2014) and examining fishing practices along the south coast of Barcelona (Maynou et al. 2011), no research has yet explored the presence of SBS in the city.

In this study, we investigate whether SBS occur in the fishery sector of Barcelona. To achieve this, we contrasted fishery-independent abundance data from fish stock assessments, which were compiled by combining data from the General Fisheries Commission for the Mediterranean (GFCM) and the Spanish Institute of Oceanography (Instituto Español de Oceanografia-Consejo Superior de Investigaciones Científicas; IEO-CSIC), with data gathered through semi-structured interviews that captured the fishermen’s perceptions of quantitative changes in marine species abundance taken place over the past decades. We proposed that, despite the city of Barcelona and its harbor having experienced heavy urban and social-ecological transformations in recent decades, owing to the solid historical and cultural fishing heritage in this community, FEK has been transmitted through generations and SBS does not occur in this fishery.

METHODS

Study area

This research was primarily conducted within the old port area (Port Vell) of Barcelona (Spain). The city of Barcelona is endowed with four distinct ports, with three serving as central hubs for industrial activities because they have multiple terminals catering to different types of cargo shipping and cruise operations, and one fishing port that is Port Vell, renowned as the historic port of the city. We focused on the historic Port Vell because of its ancient fishing traditions and heritage (Fig. 1C). In the Barcelonian culture, and particularly in the neighborhood of Barceloneta, the traditional fishery district, Port Vell is recognized to hold the strongest sociocultural memory associated with the fishing industry, especially the SSF sector.

According to “Cofradía de Pescadores de Barcelona,” the fishers’ organization regulating the fishery activities and fishers’ rights on the territory of Barcelona, the port counts a total of 308 active fishers and a fishing fleet made up of 10 trawling vessels, 11 purse seine vessels, one boat performing trammel net fishing, and one boat performing long line fishing. The fleet is characterized by boats that do not exceed 27 m in length and 850 horsepower, and small crew sizes. The average crew is 4 to 5 people for trawlers, 14 people for seiners, and 2 to 3 people for small-gear boats. The average trip length consists of 10h/day for a maximum of 263 days per year. The Barcelona fishery includes both small-fishery gear vessels (e.g., longlines, trammel nets) and more technologically advanced vessels (e.g., trawlers, purse seiners), with the latter being the primary fishing activity. Consequently, perceptions are largely shaped by fishermen involved in these semi-industrial fisheries.

Data collection

Semi-structured interviews

We organized data collection in two stages. The first stage took place from March to May 2021. During this period, we prepared for the fieldwork and got detailed information on the fishers’ community of Port Vell by conducting four online in-depth interviews with local experts on the fishery in Barceloneta. We performed background interviews with three women and one man who were involved in a wide range of activities related to the fishery sector of Barcelona (see Appendix I). The first interviewee was an artist who carried out photographic projects with the fishers’ community of Barceloneta. The second interviewee was a boat owner whose family had been involved in fishery for generations before her. The third interviewee was involved in the revalorization of local cuisine and food security initiatives. The fourth interviewee was a researcher who works in the Spanish fishery sector. The respondents offered diverse perspectives, enabling us to establish a comprehensive social-ecological understanding of the fishery sector in Barcelona. These included the potential impacts affecting the SSF sector, the challenges that it encounters, and the adaptation strategies being implemented by the fishermen. Further, the interviewees also provided phone contacts of local fishers that allowed us to engage with the fishers’ community directly.

The second stage took place in May and June 2021 and consisted of 20 semi-structured interviews (SSIs) with fishers of the Port of Barcelona. We used the help of previously interviewed fishers as intermediaries to meet and interview new fishers, a sampling technique called “snowball sampling” (Naderifar et al. 2017, Martins et al. 2018). The snowball method permitted recruiting new contacts at the end of each interview. We carefully selected participants to ensure representation of all fishing techniques practiced in the Barcelona port. These included trawling, purse seining, longlining, and trammel net fishing. Our sample comprised 20 fishermen, with 8 involved in bottom trawling, 8 involved in purse seining, 2 involved in longlining, and 2 in trammel net fishing. Interviewees were all men because no fisherwomen were present in Barceloneta harbor at the time of the data collection. Participants were primarily Spanish, with one exception from Morocco. The age range of the interviewees spanned from 26 to 86 years, consisting of 10% of fishermen below the age of 40, 70% aged between 40 and 60, and 30% aged over 60. All involved fishers started fishing between the ages of 16 and 18 years old. Most fishermen interviewed (19 out of 20) reported having a fishing experience ranging between 20 and 40 years.

Most of the interviews took place at Port Vell, which is restricted to authorized people. Thus, an official authorization was released to allow us to physically conduct interviews with local fishers. At the time of conducting the interviews, certain COVID-19-related restrictions were in effect, such as limitations on the number of people permitted to enter the port. As a result, on a few occasions, the interviews were conducted in alternative locations near the port that were familiar to local fishers, such as fishers’ bars or the fish market.

The SSI were built based on the procedure described by the Fisheries Protocol of the Local Indicators of Climate Change Impacts (LICCI) project led by the Institute of Environmental Science and Technology (ICTA) at the Universitat Autònoma de Barcelona (UAB; Reyes-García et al. 2021). The methodological approach followed the recommended guidelines for ethical and technical procedures (Bunce 2000) including random or snowball sampling techniques to interview most of the fishing community members, fish photographs with common and scientific names, and local species guides to better identify the species we followed in the present study to present a coherent overview of the long-term changes in fish abundance and to minimize the occurrence of bias during data collection. Yet, few studies have been able to use all such methods simultaneously (Hardt 2009, Usseglio et al. 2016). SSI is a standard ethnographic method for gathering information and can use both an open-ended and close-ended (yes or no questions) format (Clifford et al. 2016, Adeoye-Olatunde and Olenik 2021).

The interviews included 45 questions and were organized in three sections designed to obtain (1) fishers’ personal information, i.e., age, years involved in the fishery, (2) fishers’ opinions about the drivers of changes affecting the marine environment and fish stocks, and (3) fishers’ perceptions of quantitative changes measured in terms of tonnage percentage variation, of 50 commercially important marine species in the Catalan Sea (see Appendices 2, 3, and 4). These assessments covered a time frame that captured both past and present fish stock conditions. During the interviews, the words “past” and “present” were used to help the interviewees recall historical information about “how it was” (from the time fishermen can recall) and make comparisons with “how it is” nowadays. All the fishermen interviewed consistently indicated the early 1990s as the period representing past conditions, while the present conditions discussed in the interviews pertained to the year 2021, when the interviews were conducted. Therefore, in this paper, we use the words “past” and “present” to refer to these time frames.

The average duration of the interviews was approximately one hour. Also, we did not record SSIs and anonymized all data to enable people to speak more freely without the fear that their voices would be misused. All information given by the fishers was treated anonymously and is protected under the Organic Law 15/1999 from 13 December about Personal Data Protection in Spain.

Building the biological dataset

After the initial selection of 50 marine species (Appendix 4), our analysis narrowed down to six species: European hake (Merluccius merluccius), Norway lobster (Nephrops norvegicus), Red shrimp (Aristeus antennatus), Red mullet (Mullus barbatus), European anchovy (Engrauils encrasicolus), European pilchard (Sardina pilchardus). We selected these species for two reasons: (1) scientific data were available only on these species, and (2) they are the most commercially relevant in Catalonia (see Appendix 4), thus fishers readily tend to notice changes in their abundance and location.

It is important to note that the selected species exhibit distinct ecological behaviors, categorized as either pelagic or benthic. Consequently, different fish-stock assessment methodologies are employed for their stock assessment. Pelagic species in the Mediterranean Sea are typically assessed using acoustic surveys, such as the MEDiterranean-International Acoustic Survey (MEDIAS; Giannoulaki et al. 2021), whereas bottom trawl surveys, like the International Bottom Trawl Survey in the Mediterranean (MEDITS), are utilized for assessing benthic species (Bertrand et al. 2002, Spedicato et al. 2019). To contrast the fishers’ perception of quantitative changes in marine species abundance with scientific information, we utilized fish stock assessment data, requested from scientists of the IEO-CSIC, for this study, as well as the open-source GFCM fish stock assessment data (Giráldez et al. 2017, Torres et al. 2017). The two datasets used in this study covered the period from 1994 (when MEDIAS and MEDITS surveys commenced) to 2021 and currently represent the only available sources of quantitative information for evaluating the changes in abundance of the six marine species under investigation (Payne et al. 2008, Demirel et al. 2020). Stock assessment data for benthic species (M. merluccius, N. norvegicus, A. antennatus, and M. barbatus) were obtained from the IEO-CSIC dataset, based on the MEDITS survey. Data for commercially important pelagic species (E. encrasicolus and S. pilchardus) were sourced from the open-access GFCM dataset, derived from the MEDIAS survey (Giráldez et al. 2017, Torres et al. 2017). We combined the IEO-CSIC and the GFCM datasets into an integrated biological dataset (hereafter referred to as “biological dataset”) to obtain complete coverage of the six species under investigation and encompassed the target historical period spanning from 1994 to 2021, aligning with the past and present references indicated by the fishermen.

Data processing and analysis

Assessing fishermen’s perception of change in species abundance and their level of agreement

In order to evaluate the perceptions of fishermen regarding shifts in the abundance of marine species over time, we asked them to indicate the perceived percentage change in the abundance in their catch (measured in tons) of six specific species between present and past conditions. The provided percentage changes were then categorized into five distinct groups to capture potential trends: (i) decrease by > 0–50%, (ii) decrease by > 50–100%, (iii) increase by > 0–50%, (iv) increase by > 50–100%, (v) no change (Table 1). Then we created a ranking by calculating the proportion of the fishermen who gave the same answer. The categorization of the percentage of responses was necessary to (1) ensure that the perception of change was overall consistent across fishermen (i.e., > 50% of participants sharing the same perception) and (2) build a consistent dataset derived from the interviews to compare against biological data.

Evaluating changes in abundance within the biological dataset

The biological dataset spans the period from 1994 to 2021. To align with the temporal conditions identified by the fishermen as “past” and “present,” we designated 1994–2000 as represent past conditions and 2015–2021 to reflect present-day conditions within the dataset.

We derived averaged values that most effectively captured historical and current conditions by computing the percentage difference in species abundance (measured in metric tons) between those two time series periods only: the average of the earliest (corresponding to the stock assessment surveys conducted between 1994 and 2000) and the most recent (corresponding to the stock assessment surveys conducted between 2015 and 2021) data points. Hence, we created a historical reference (1994–2000) and a contemporary reference (2015–2021) for the biological dataset, aligning with the conditions specified by the fishermen for both the past and present. These two temporal references were chosen in order to compare the variation in mean biomass between the same time period in the fishermen’s perception and the biological data.

Assessment of the shifting baseline syndrome

To determine the occurrence of SBS we contrasted the percentage change in species abundance between the two chosen periods, as obtained from both the reports provided by the fishermen and the biological dataset. This comparison was performed by utilizing a Kruskal-Wallis test, which was executed using the kruskal.test function in R. We specifically chose this non-parametric test for three reasons: (1) the data exhibited an asymmetrical distribution, (2) there were relatively few observations per fishing gear type (i.e., long line and trammel net), and (3) because it allowed comparing the median, which is less affected by anomalous values compared to the mean. All the analyses were performed using R (RStudio version 4.2.2).

RESULTS

Assessing changes in marine species abundance over time

Fishers’ agreement

We found that 32% of fishermen perceived a moderate decrease (< 0–50%) compared to historical conditions, while 26% perceived a high decrease (< 50–100%) in marine abundance over the investigated historical period. The category “no changes” was cited by 29% of fishermen, while only a small number (13%) of fishermen perceived a moderate increase (> 0–50%). No fishermen perceived an increase higher than 50% (high increase) or experienced no catches in the species selected (Fig. 2). Specifically, for E. encrasicolus the most frequently cited category was “50–100% decrease” (60%) followed by “0–50% decrease” (40%); for S. pilchardus the most frequently cited categories were both “0–50% decrease” and “50–100% decrease,” followed by “no change” (14%); for M. merluccius the most frequently cited categories were “0–50% decrease” and “50–100% decrease,” with same percentage (50%); for M. barbatus the most frequently cited categories were “0–50% decrease” and “no change,” with same percentage (50%). Whereas for A. antennatus and N. norvegicus, the interviews also revealed that certain marine species have experienced an increase in their catch volumes over the years, albeit with less agreement among the fishermen. For these species frequently cited categories were “no change” (63%), followed by “0–50% increase” (25%) and “0–50% decrease” (13%, see Appendix 5, Fig. S1).

Fishers’ perception of changes in target species

Fishermen reported a general decline in the abundance of target species (measured in tons) when comparing current conditions to the past, reflecting reduced availability in recent times. On average, they noted declines of 47% for E. encrasicolus, 37% for S. pilchardus, 58% for M. merluccius, and 13% for M. barbatus. Conversely, for A. antennatus and N. norvegicus, fishermen observed an increase in abundance, estimating rises of 5% and 8%, respectively. Additionally, our findings indicate that a majority of fishermen (58%), in each fishing gear group, perceived a decline in the abundance of marine species compared to past conditions and that most of the responses belonged to the category of change “moderate decrease.”

In addition, increasing marine pollution, stemming from domestic, transportation, industrial, and agricultural sources, along with escalating land and sea use changes driven by coastal urbanization and the expansion of industrial facilities (e.g., the airport and commercial port of Barcelona), emerged as the primary drivers of change identified by local fishermen (more than 50% of the fishing community in agreement). Overfishing, climate change, and invading alien species were also considered as potential drivers of change, although there was less consensus among the fishermen (agreement among the fishing community of 20–35%). Conversely, the observed increasing trends in A. antennatus and N. norvegicus were ascribed to a heightened focus on targeting these specific species, especially in the last few decades.

Changes in abundance from species stock assessment

The examination of the estimated biomass derived from the biological dataset on fish stock assessment over time revealed significant fluctuations in species abundance (see Appendix 5, Fig. S2). A comparison between historical (1994–2000) and present (2015–2021) conditions indicates changes in abundance trends for the studied species (Table 2). Specifically, S. pilchardus experienced a 69% decrease, while E. encrasicolus saw an increase of more than 100%. M. merluccius decreased by 21%, whereas M. barbatus exhibited more than 100% increase. Additionally, A. antennatus and N. norvegicus both showed increases of 34% and 11%, respectively, when present conditions are compared to past conditions (Table 2).

Contrasting changes between fishermen’s perception and biological data.

Overall, the fishermen’s perception shows similar trends for some species and contrasting trends for others when compared to the stock assessment data. The comparison between the observed changes in the five investigated marine species’ abundance as perceived by the fishermen and as estimated based on the biological dataset is shown in Figure 3.

In accordance with the biological dataset, fishermen perceived a decreasing abundance trend for M. merluccius and S. pilchardus and an increasing trend, albeit much lower if compared to biological data, for A. antennatus and N. norvegicus over the selected historical period (Fig. 3). However, E. encrasicolus and M. barbatus were perceived to be decreasing by the fishermen, while the biological data showed an increasing trend in abundance (Fig. 3). Nevertheless, results from the Kruskal-Wallis rank-sum test conducted on the overall investigated species indicated an absence of significant differences in the fishermen’s perception of quantitative changes in abundance over the selected historical period (p = 0.41).

DISCUSSION

The present work provides new insights into the capacity of Barcelona’s semi-industrial fishing community to detect and monitor shifts in the abundance of commercially relevant marine species’ populations. Overall, our results show no significant differences between the fishers’ perception and the biological data, suggesting that SBS is not noticeably occurring in this fishery. Nevertheless, findings also indicate a disparity between fishermen’s perceptions and the biological dataset for some of the assessed species. Specifically, although fishermen’s perceptions aligned closely with the observed changes in abundance for four species over the past three decades, contrasting results were reported for two species. Our results contrast with previous studies that revealed the presence of SBS in other fishing communities worldwide (Pauly 1995, Ainsworth et al. 2008, Pinnegar and Engelhard 2008, Bender et al. 2014, Giglio et al. 2015, Ulman and Pauly 2016, Zapelini et al. 2020) but are in line with works performed on the Mediterranean coasts of Spain, which also showed that fishers’ perceptions are in accordance with other quantitative information such as landings (Leitao et al. 2020) and stock assessment (Bastari et al. 2022) confirming the important role of FEK for fisheries assessments.

Fishermen were able to detect declining trends in some of the investigated marine species’ populations (i.e., S. pilchardus and M. merluccius), which according to them were driven by the current multi-lateral anthropogenic impacts including increased marine pollution and coastal transformations, as strongly stressed by previous studies in the region (Carbonell 2014). Particularly, the 1990s and 2000s are described by fishermen as a historic period in which Barcelona experienced one of its greatest industrialization moments due to the Olympic Games of 1992, as well as the port and airport enlargement projects following commercial and tourism expansion. Fishermen also observed increasing trends in the abundance of target species, specifically A. antennatus and N. norvegicus, attributing this to a rise in catches driven by market demand for these species in recent decades. This aligns with the rising trend in landings observed in the Catalan Sea (Carbonell et al. 1999, Maynou 2008). This observation aligns with findings from stock assessments, which classified the two shrimp stocks as “low overfished,” that is, their current state of the stock (in biomass) arises from the application of excessive fishing pressure in previous years (Esteban 2020a, 2020b). Nevertheless, it appears that the increasing catches do not significantly affect the overall abundance of these species, possibly because of strong fluctuation patterns, as observed for A. antennatus in the Catalan Sea (Maynou 2008). This could be linked to a higher nutrient availability following increased occurrences of oceanographic dynamics in specific regions of the Catalan Sea (Cartes et al. 2008, López-Jurado et al. 2008) or to the generally high environmental variability in marine ecological processes within the region, yet to be fully understood (Maynou 2008).

However, for two of the species, the European anchovy (E. encrasicolus) and the red mullet (M. barbatus), biological data and fishers’ perceptions reflected opposing tendencies. According to fishermen, these species are decreasing, whereas according to biological data, they have noticeably increased over the last decades (Bastari et al. 2022); contradicting results between fishers’ perceptions and available data for M. barbatus in the Ebro Delta Region in Spain were also reported. In particular, although earlier studies found that fishers’ perceptions align predominantly with the scientific information regarding the increase in M. barbatus stock biomass, some participants in these studies also indicated a decreasing trend, which might be attributed to varying local trends and natural distribution of this species (Tserpes et al. 2019). For instance, the genetic distribution of M. barbatus was observed to be highly structured, resembling a meta-population with independent, self-recruiting sub-populations connected to some extent (STECF 2023).

One explanation regarding contrasting results between FEK and scientific data is that, in some cases, the geographical scale used can vary, and changes in local distribution cannot be captured by biological data (Bastari et al. 2022). FEK typically concentrates on smaller, localized areas, such as fishers’ fishing grounds, whereas scientific assessment often adopts a broader perspective covering larger scales. In our study, fishermen’s perceptions of changes are limited to their fishing areas, spanning approximately from Tarragona to Badalona, covering about 100 km. In contrast, the scientific stock assessment was based on a wider area (FAO geographical sub-area 6), stretching from Sagunto (Valencia) to Cap de Creus (Girona), covering approximately 500 km, because of scientific surveys being conducted at the GSA level. This difference in the size of reference areas may lead to scientific assessments potentially overlooking fluctuations in local abundance trends, and observations that fishermen may have made and reported during the interviews.

A further explanation for the observed mismatch between fishermen’s perception and biological data, is that individuals can be an indication of the emergence of personal amnesia, which occurs when individuals do not have an accurate perception either of the past or current day (Papworth et al. 2009). Although we did not find statistically significant differences between fishermen’s perceptions and biological data overall, the observed discrepancies regarding historical and current quantitative changes in some species’ abundance, coupled with the demographic disparity between younger fishermen (under 40 years old, 10% of those interviewed) and older fishermen (over 40 years old, 90% of those interviewed), are ground for concerns. These trends might lead to a gradual erosion of fishermen’s perceptions of normal environmental conditions and increase the risk of SBS in the long term. We suggest that future studies focusing on single species could be undertaken because they have the potential to offer higher resolution information regarding fishermen’s perceptions as well as help mitigate additional biases, such as variations in fishermen’s priorities for capturing specific species for commercial purposes.

The general environmental degradation conditions that the Mediterranean Sea is currently facing require urgent international, national, and local conservation strategies (Halpern et al. 2008, 2015, FAO 2020). It has been argued that the management system implemented in the Mediterranean region might be too slow and probably inadequate to protect biodiversity and secure fishery resources for future generations (Colloca et al. 2017). Such conservation commitments should include a thorough understanding of historical and current environmental conditions and the participation and implication of a diversity of social actors (Shackeroff and Campbell 2007). Given the current stock assessment data deficiency for the Mediterranean, it is advisable to incorporate complementary sources of knowledge, including local ecological knowledge (e.g., FEK) and local communities, in the decision-making process for effective fishery management. Moreover, integrating FEK is not solely advantageous for the scientific community but also serves as a means to empower communities in decision making regarding the natural resources they traditionally utilize and are often excluded from. Therefore, it is not merely about incorporating knowledge but also about integrating communities and legitimizing their knowledge (Silvano and Valbo-Jørgensen 2008, Zukowski et al. 2011, McQuatters-Gollop et al. 2019, Leitao et al. 2020). In our study, we did not find significant evidence of SBS, although we did observe divergent trends in two of the species stocks. We emphasize the potential contribution of local knowledge (i.e., FEK) in offering valuable insights for the reconstruction of historical fish abundance trends, particularly for those species whose perception of change is consistent with biological data. Furthermore, involving the professional fishing sector and incorporating FEK into marine resources co-management schemes is recommended for future efforts because it could complement information valuable to decision makers, as highlighted by other studies that have proven the effectiveness of this approach in supporting sustainable solutions for fishery and marine ecosystem management in Catalonia (Lloret et al. 2020, Druon et al. 2023) and other regions (Sáenz-Arroyo and Revollo-Fernández 2016, McQuatters-Gollop et al. 2019, Leitao et al. 2020).

CONCLUSION

According to Papworth et al. (2009), the empirical demonstration of SBS involves proving the presence of biological changes in the system and showing that the perceived changes align with biological data. This study is the first to empirically assess the presence of SBS in the fisher community of Barcelona (Spain) by comparing scientific (fishery-independent) data with FEK-derived data. Overall, fishermen’s perceptions of abundance changes are comparable to historical stock assessment data, suggesting that SBS is not occurring in this fishery. Although our overall results indicate that fishermen’s perception of quantitative changes in marine species abundance over a nearly 30-year time frame is not subject to substantial biases, several inconsistencies are noted. We draw attention to the risk that SBS may arise in this fishery in the future because of observed signs of potential personal amnesia along with a lack of generational turnover. In conclusion, despite the recognition of FEK as an important component in the quantitative understanding of marine resource abundance over the chosen historical period, we also stress the necessity to consider, quantify, and monitor the potential presence of SBS in the first place if fishers’ FEK is meant to complement or boost scientific knowledge.

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