Elasmobranchs, which include sharks and rays, are one of the planet’s most ancient vertebrate groups, dating back approximately 400 million years (Andreev et al., 2015). Sharks play fundamental ecological roles in marine environments, shaping the structure of marine food webs and contributing to the maintenance of balance and diversity in marine ecosystems (Roff et al., 2016). However, the future of elasmobranch species has been threatened due to the global expansion of fishing practices (Myers, Worm, 2005). In addition, life history traits such as slow growth and reproductive rates make them highly vulnerable to overexploitation (Worm et al., 2013). On the other hand, there are several examples of non-extractive use of sharks through diving tourism, generating economic benefits while promoting shark conservation (Torres et al., 2017; Zimmerhackel et al., 2019). Despite that, fishing pressure and human consumption continue to pose threats to shark populations at a global scale (Dulvy et al., 2014; Dent, Clarke, 2015; Davidson et al., 2016; Pacoureau et al., 2021). This pressing issue highlights the immediate necessity for conservation efforts and sustainable management strategies to protect these ancient and ecologically vital species.

Brazil is one of the world’s largest consumers and importers of shark meat and other by-products (Dent, Clarke, 2015; Bornatowski et al., 2018). For example, the average annual production of elasmobranchs represented 21,127 tons from 2000 to 2003, which corresponded to ~4.3% of the total fish production for that period (Brasil, 2014). Such catches mostly supply meat consumption and the fin trade (Barreto et al., 2017), both of which have been shown to be major drivers of shark population decline worldwide. Over the past few decades, the shark meat trade has seen a rise, which is closely associated with the increased import of shark meat into Brazil (Dent, Clarke, 2015). This increase in demand could be an outcome of the implementation of shark finning restrictions, as it has incentivized the complete utilization of sharks, thus exposing the resource to a new source of exploitation (Pincinato et al., 2022). Despite the growing shark meat trade in Brazil, there is a lack of accurate, species-specific fishing data, which often hampers quantitative stock assessment.

Landing data are fundamental for assessing and managing fisheries. However, long-term data series are mostly available for high-income countries in the northern hemisphere (Beaudreau et al., 2014). In low and middle-income countries, it is typical to have either non-existent monitoring or fragmented data where landings are not described at species level (Bornatowski et al., 2014a; Freire et al., 2021). Implementing fisheries monitoring programs in countries with limited resources, where fisheries are complex and involve multiple gears and species, poses a significant challenge (Beaudreau et al., 2014). Data-poor scenarios hide the magnitude of impacts derived from fishing activities. Alternatively, non-conventional approaches have been used to circumvent the difficulties imposed by the lack of fisheries landing data (Eddy et al., 2010; Paterson, 2010; Tesfamichael et al., 2014). These include historical information accessed from the gray literature, local ecological knowledge (LEK) of resource users (Sáenz-Arroyo et al., 2005; Taylor et al., 2017), old photographs (McClenachan, 2009), and logbooks (Martínez-Candelas et al., 2020), all can be valuable sources. Fisher’s LEK may reveal fisheries catch trends, habitat preference, migration patterns, and changes in body size of targeted species (Braga et al., 2018; Leduc et al., 2021). Indeed, fishers’ LEK studies have been proved critical to inform on the collapse of marine resources (Venkatachalam et al., 2010; Nazareth et al., 2022). In Brazil, fishers’ knowledge has helped to reveal past scenarios of marine stocks, circumventing the difficulties caused by the lack of fishing data (Giglio et al., 2015; Silvano et al., 2017; Fogliarini et al., 2021).

Fishers’ knowledge has contributed to our understanding of shark biology, ecology, and conservation in numerous cases. In Fiji (South Pacific), fishers’ LEK revealed the presence of large sharks (e.g., Sphyrna spp.) near river mouths, providing reliable information on shark occurrence (Rasalato et al., 2010). In the Mediterranean Sea, the empirical knowledge of fishers helped reconstruct angel shark catches (Squatina spp.) in the last six decades, providing important data on a highly threatened fish taxonomic group (Giovos et al., 2019). In the Strait of Sicily, also in the Mediterranean Sea, interviews with fishers were used to reconstruct abundance trends of shark populations over six decades (Colloca et al., 2020). Fishers reported that shark catches have diminished since the 1940s and commercially important species have been depleted or locally extinct. In Brazil, fishers’ LEK revealed historical decreases in the body size of sharks (Giglio et al., 2015; Leduc et al., 2021). Given the absence of historical data on shark catches, we investigated temporal and spatial patterns of catches of coastal sharks in Arraial do Cabo, Brazil, as determined by local ecological knowledge of fishers. We provide data that can inform conservation and management measures, and guide research focusing on these species.

Study site. Arraial do Cabo, located in the state of Rio de Janeiro, southeastern Brazil (Fig. 1), is known as a historical fishing area that is home to people that use of beach seine, line and hook, gill nets, and spears among other equipment types (Barreto et al., 2019). The use of beach seine is a secular fishing practice in the region and has been used to catch several pelagic species (i.e., jacks, blue fish, mullets, scombrids) and sharks. Historically, the most important species for local fishing are groupers (e.g., Epinephelusmarginatus (Lowe, 1834), Mycteroperca acutirostris (Valenciennes, 1828)), jacks (Caranx spp.), Seriola spp.), mullets (Mugil liza Valenciennes, 1836) and blue fish (Pomatomus saltatrix (Linnaeus, 1766)) (Bender et al., 2014; Fogliarini et al., 2021). In 1997, Arraial do Cabo became a partially protected marine area, the Marine Extractive Reserve of Arraial do Cabo (RESEXMar). Despite its status as a marine protected area, the RESEXMar lacks designated no-take zones, and enforcement for threatened species is poorly applied. The region is influenced by upwelling events (Valentin, 2001) and is considered a transition zone between the tropical and subtropical provinces, rendering Arraial do Cabo a hotspot of marine biodiversity in the Brazilian Province (Cordeiro et al., 2016). In addition to fishing, the region has shown an intense coastal tourism, with consequences that include disturbance due to excessive noise, increasing production of solid and liquid wastes, compromising the health of corals (Rogers et al., 2014) and other benthic organisms (Cassola et al., 2016).

Data collection. Individual face-to-face interviews through semi-structured questionnaires were conducted with 155 small-scale fishers between July 2018 and July 2019 in six fishing communities: Figueira, Monte Alto, Praia Grande, Praia dos Anjos, Prainha, and Praia do Pontal (Fig. 1). Questionnaires included a general question (e.g., which species of sharks were the most frequently caught during their fishing careers) and specific questions targeting three shark species, the spinner shark (Carcharhinus brevipinna (Valenciennes, 1839)), the shortfin mako shark (Isurus oxyrinchus Rafinesque, 1810), and the sandbar shark (Carcharhinus plumbeus (Nardo, 1827)) (Tab. S1). Due to the richness of common names for Brazilian fish, we used photographs to enable shark species identification during the interviews (Freire, Carvalho-Filho, 2009). When fishers recognized and had already captured any of these species, he was asked about: i) the best day catch (number of individuals), ii) the site, iii) and the year in which this catch was made. In addition, we asked about the fisher’s age and experience in fishing (e.g., years of practice). During interviews, fishers provided general information about the species’ breeding season, feeding behavior and other ecological aspects. This information was registered as observations (Tab. S2). We assessed the threat categories according to the Global Red List (IUCN, 2023) and the National Red List of Threatened Species (MMA, 2018, 2023) for all species mentioned by fishers. The fishers were informed of the research purpose before each interview. We also informed them that all information provided in interviews would be anonymized.

Data analysis. From the information on the best day catch obtained through interviews with local fishers, we estimated the temporal decline in catches of each shark species. For that, we applied regressions and plotted the best day catch (number of individuals) versus the year in which such catch occurred. We tested distinct regression types (exponential, polynomial, and linear regressions) and values of coefficient of determination were compared to assess the quality of the regression fit to data distribution.

To analyze changes in spatial distribution of best day catches we use a nautical chart (Fig. S3) of the region. Interviewees were asked to mark in the chart the sites where they caught shark species (Fig. S3). To compare past and present periods, we grouped fisher’s reports in two different periods: before 2006 and after 2006. We established this division because in 2006, Alkalis Company, an important local producer of calcium carbonate, closed. After this event, the municipality’s economy experienced an exponential increase in fishing, once again making it the predominant activity in the primary sector (Carneiro et al., 2012). As a result, many people began relying on fishing as their main source of income, increasing the exploitation of marine resources throughout the region (Carneiro et al., 2012).

Maps of spatial distributions of best day catches were built using the Quantum GIS software (QGis, 2019). To verify temporal changes in spatial distribution, the catches in number of individuals were compared by fishing site/ground and period (before 2006 and after 2006). Statistical analyzes were performed using R software v. 3.6.1 (R Development Core Team, 2019).

We interviewed 155 small-scale fishers, of which their age ranged 17 to 82 years old, (average = 50 ±12 years) (±s.d.) and their experience ranged three to 64 years (average = 31 ±13 years). Fishers identified six shark species (one genus) which are considered at risk of extinction (Tab. 1). The most frequently caught sharks were spinner shark (Carcharhinus brevipinna), the sandbar shark (Carcharhinus plumbeus), and the shortfin mako shark (Isurus oxyrinchus). Of these sharks, there were no significant declines in C. brevipinna caught with beach seine (Fig. 2) and there were no significant differences over time for both C. brevipinna and I. oxyrinchus caught with hook and line (Figs. 3A, B). By contrast, the number of C. plumbeus individuals was significantly reduced over the last 50 years from an average of 9.56 ±5.13 individuals in 1968 to 2.82 ±1.7 individuals in 2019 (Fig. 3C).

Fishers’ knowledge revealed temporal changes in the fishing grounds of three investigated shark species (Fig. 4). The spatial distribution of shark catches revealed that new fishing grounds have been exploited over time. For instance, eight new fishing grounds of C. brevipinna were reported after 2006 (Figs. 4A, B). In some fishing grounds, such as Praia Grande, the number of individuals caught decreased over time (Fig. 4B). Between 1979 and 2005, beach seine fishers caught around 2000 individuals. After this period (2006–2019), the number of individuals declined to a maximum of 500 individuals caught on the best day’s catch (Figs. 4A, B). The number of fishing grounds where the interviewees reported catches of I. oxyrinchus also increased; six new sites appeared from 1962 to 2019 (Figs. 4C, D). Finally, for C. plumbeus, four new fishing grounds were reported after 2006. In Praia Grande, where 11–12 individuals were caught between 1968 and 2005, no C. plumbeus individuals were captured between 2006 and 2019 (Fig. 4F).

During the last 60 years in Arraial do Cabo, shark catches and fishing grounds have changed. Fish stocks have experienced changes in this region (Fogliarini et al., 2021), where target top and mesopredators, such as sharks, groupers, and tunas, have declined and fishers have concentrated on new ones (Bender et al., 2014; Fogliarini et al., 2021). In general, shark fisheries have changed over time. A small portion of the fleet currently focuses on shark fishing seasonally, operating fishing grounds located farther away from the coast to maintain profitability. However, despite the increased effort, this has not resulted in a corresponding increase in catches. Our research, in fact, has revealed a decline in the number of sharks caught in some fishing grounds closer to the coast. Fishers reported the best day catch of over 2,000 sharks using beach seine at Praia Grande beach. Due to unsustainable captures, catch events with hundreds of individuals have become increasingly rare (Fig. 5).

Off the Brazilian coast, catches on pregnant sharks, including juveniles and immature individuals using beach seine and other gill nets are common (Vooren, Klippel, 2005; Yokota, Lessa, 2006; Bornatowski et al., 2014a). We verified that pregnant individuals of C. brevipinna and I. oxyrinchus were frequently captured between June and July (Tab. S2). Patterns of reproduction, migration, and feeding habitats of these shark species are poorly known for the Brazilian Province. In South Africa, the capture of pregnant C. brevipinna was confirmedin beach nets between March and August (Allen, Gliff, 2000). In our study, fishers also reported large catches of this species during upwelling events and following large mullet shoals (Mugil sp.) (Tab. S2). According to reports, sharks are attracted to the coastline to feed on mullets, typically occurring between April and August. Along the African coast, spinner sharks were captured during feeding aggregations, especially in austral winter months, also coinciding with the abundance of sardines (Sardinops sagax) in coastal waters (Allen, Gliff, 2000). This feeding aggregation behavior has also been observed in Florida, where C. brevipinna formed “packs” behind shrimp boats (Dodrill, 1977).

Shark fishing in Arraial do Cabo sustained an international shark finning market until the 1990s, when this market was banned in Brazil (Amorim et al., 1998; Hazin et al., 2008). As in other countries, management of shark fishing in Brazil has not prevented population declines (Bornatowski et al., 2014a,b). By 2018, the National Red List of Threatened species included 30 shark species (MMA, 2018). In 2023, five other species were added to this list. Among these, the spinner shark, C. brevipinna, categorized as Vulnerable (VU), and the shortfin mako I. oxyrinchus, listed as Critically Endangered (CR) (MMA, 2023). The spinner shark is a common coastal-pelagic species that occurs in warm-temperate and tropical areas of the Western and Eastern Atlantic and the Western Indo-Pacific (IUCN, 2023). This species is highly susceptible to fisheries due to its low biological productivity, and its breeding area which overlaps with areas of intensive and unregulated fisheries (Diop, Dossa, 2011; Doumbouya et al., 2017). A global estimate suggests that spinner shark populations have suffered reductions of 30–49% in the recent decades (IUCN, 2023). Similarly, studies have indicated the depletion of shortfin makostocks in various marine regions, including the South Atlantic (Ferretti et al., 2008; Barreto et al., 2016; ICCAT, 2017; Brunel et al., 2018). An assessment has revealed a 99% decline in the average CPUE (Catch per unit effort) of shortfin mako caught in longline fisheries over the last 30 years (Barreto et al., 2016).

In conclusion, we observed a shift in shark fishing practices in Arraial do Cabo over the past 60 years. The shark fleet has moved further away from the coast due to overexploitation. However, this change has not been accompanied by an increase in catches. A fundamental step in managing the cross-scale overfishing scenario for sharks in Brazil is the establishment of protected areas in nursery and breeding sites. However, given that most of these sharks exhibit high mobility, migrating through long distances during their life cycle, which includes feeding and breeding areas (Capapé et al., 2003; Stevens, 2008; Letessier et al., 2017), effective protection for these species will solely be effective though a network of protected areas and shark fishing bans, coupled with effective monitoring and education initiatives. Since 2007, Brazil has lacked a systematic nationwide fishing monitoring program (IBAMA, 2007), lacking basic data to support fisheries management. We strongly recommend that the Brazilian government accelerates the establishment of monitoring programs, integrating scientific guidance, stakeholders’ knowledge, and leadership. Alarmingly, increasing evidence indicates a decline in fish stocks targeted by both industrial and small-scale fisheries along the Brazilian coast (Freire et al., 2021). Additionally, shark species and other targeted fisheries such as groupers possess life history traits that render them even more susceptible to fishing impacts (Bender et al., 2013; Ceretta et al., 2020). Fisheries landing data across long time-series also remain scarce for sharks in Brazil. However, through fishers’ LEK, we may fill in gaps in fisheries landing data for some species. Combining different data sources can help us improve our understanding of shark population trends in complex and multi-specific fisheries. This approach can provide insight into data-poor sites where information is absent or fragmented over time. Biological and social approaches are complementary, and their integration has gained increased recognition, providing relevant information for fisheries management and the conservation of threatened species. The public in general is unaware about the key role of top predators like sharks. This fact reinforces the constant need for public awareness to value sharks alive, considering the multiple examples of revenues where sharks are protected (Vianna et al., 2018; Gonzáles-Mantilla et al., 2022). These recommendations collectively underscore the need for a holistic approach that integrates various strategies and stakeholders to ensure the sustainability and conservation of Brazil’s shark populations.