Changes in the users of the social-ecological system around a reciprocal human-dolphin relationship

Abstract

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1. In contrast to many contemporary negative human-nature relationships, Indigenous Peoples and Local Communities have stewarded nature through cultural practices that include reciprocal contributions for both humans and nature. A rare example is the century-old artisanal fishery in which net-casting fishers and wild dolphins benefit by working together, but little is known about the persistence of the social-ecological system formed around this cultural practice.
2. Here, we frame the human-dolphin cooperative fishery in southern Brazil as a social-ecological system based on secondary data from the scientific and grey literature. To investigate the dynamics of this system, we survey the local and traditional ecological knowledge and examine potential changes in its main component—the artisanal fishers—over time and space.
3. Over 16 years, we conducted four interview campaigns with 188 fishers in fishing sites that are more open (accessible) or closed (restricted) to external influence. We investigated their experience, engagement and economic dependence on dolphin-assisted fishing, as well as the learning processes and transmission of the traditional knowledge required to cooperate with dolphins.
4. Our qualitative data suggest that fishers using accessible and restricted fishing sites have equivalent fishing experience, but those in more restrictive sites tend to be more economically dependent on dolphins, relying on them for fishing year-round. The traditional knowledge on how to cooperate with dolphins is mostly acquired via social learning, with a tendency for vertical learning to be frequent among fishers using sites more restrictive for outsiders. Experience, economic dependence and reliance on vertical learning seem to decrease recently, especially in the accessible site. Our quantitative analyses, however, suggest that some of these fluctuations were not significant.
5. Our study outlines the key components of this social-ecological system and identifies changes in the attributes of a main component, the users. These changes, when coupled with changes in other components such as governance and resource units (fish and dolphins), can have implications for the persistence of this cultural practice and the livelihoods of Local Communities. We suggest that continuous monitoring of this system can help to safeguard the reciprocal contributions of this human-nature relationship in years to come.

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Resumo

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1. Em contraste com muitas relações contemporâneas negativas entre humanos e a natureza, os Povos Indígenas e Comunidades Locais têm interagido com a natureza através de práticas culturais que incluem contribuições recíprocas tanto para os humanos quanto para a natureza. Um exemplo raro é a pesca artesanal secular na qual pescadores e botos se beneficiam ao trabalharem juntos, mas pouco se sabe sobre a persistência do sistema socioecológico formado em torno dessa prática cultural.
2. Aqui, enquadramos a pesca cooperativa entre humanos e botos-da-tainha no sul do Brasil como um sistema socioecológico baseado em dados secundários da literatura científica e cinza. Para investigar a dinâmica desse sistema, pesquisamos o conhecimento ecológico local e tradicional e examinamos possíveis mudanças em seu principal componente—os pescadores artesanais—ao longo do tempo e espaço.
3. Ao longo de 16 anos, conduzimos quatro campanhas de entrevistas com 188 pescadores em locais de pesca que são mais abertos (acessíveis) ou fechados (restritos) à influência externa. Investigamos sua experiência, envolvimento e dependência econômica da pesca cooperativa com botos, bem como os processos de aprendizado e transmissão do conhecimento tradicional necessário para cooperar com botos.
4. Nossos dados qualitativos sugerem que os pescadores que utilizam locais de pesca acessíveis e restritos têm experiência de pesca equivalente, mas aqueles em locais mais restritos tendem a ser mais economicamente dependentes da pesca cooperativa, dependendo dos botos para a pesca durante todo o ano. O conhecimento tradicional sobre como cooperar com botos é principalmente adquirido via aprendizado social, com uma tendência de aprendizado vertical ser mais frequente entre os pescadores que utilizam locais mais restritos para pescadores de fora. A experiência, dependência econômica e a dependência do aprendizado vertical parecem ter diminuído recentemente, especialmente no local acessível. Nossas análises quantitativas, no entanto, sugerem que algumas dessas flutuações não são significativas.
5. Nosso estudo delineia os principais componentes desse sistema socioecológico e identifica mudanças nos atributos de um componente principal, os pescadores como usuários deste sistema. Essas mudanças, quando combinadas com mudanças em outros componentes, como governança e unidades de recursos (peixes e botos), podem ter implicações para a persistência dessa prática cultural e para os meios de subsistência destas Comunidades Locais. Sugerimos que o monitoramento contínuo desse sistema pode ajudar a salvaguardar as contribuições recíprocas dessa relação entre humanos e natureza nos próximos anos.

1 INTRODUCTION

Contemporary human-nature relationships are often one-sided: humans gain the greatest benefits, while nature bears the greater costs (e.g. Costanza et al., 2017; Harris et al., 2023; Soga & Gaston, 2020). In contrast, some Indigenous Peoples and Local Communities have historically maintained more harmonious relationships with nature through responsible use and conservation of natural resources (e.g. Reyes-García et al., 2019; Reyes-García & Benyei, 2019). Such relationships not only sustain human livelihoods and well-being but also nurture relational values and appreciation for nature (e.g. Comberti et al., 2015; Ojeda et al., 2022). These communities have stewarded nature diversely, sometimes fostering reciprocal contributions between people and nature (Ojeda et al., 2022). Notable examples include cultural practices mediated by behaviour, where humans and wild animals cooperate by combining their complementary foraging skills for mutual benefit (Cram et al., 2022). However, changes in local livelihoods and modernisation contribute to make such human-wildlife cooperation increasingly rare (van der Wal et al., 2022), in sharp contrast with the widespread escalation of human-wildlife conflicts (Harris et al., 2023; Nyhus, 2016). Tight human-nature interactions are remarkable examples of human connectedness to nature, and they embed social, economic and environmental dimensions of sustainability, revealing direct and indirect contributions of nature to people, as well as the reciprocal contribution of people to nature. Assessing the persistence of these remaining reciprocal contributions in the face of environmental and cultural changes requires understanding the social-ecological system around them.

The social-ecological system perspective is based on an intricate interplay between sociodiversity and biodiversity, as traditional societies interact with biodiversity through adaptive and co-evolutionary processes for many generations (e.g. Holling, 1973). This perspective has been used to address complex problems associated with the human-nature relationship, including challenges in resource management and conservation processes, as well as their dynamics. It also provides a foundation for discussions about sustainability policies. By recognising humans as key components of nature (Berkers & Folke, 1998), this theoretical approach highlights their influence on the system's self-organisation and sustainability through the interconnection and feedback between social (political, economic, cultural and technological) and ecological (biotic and abiotic) processes (Folke et al., 2010; Ostrom, 2009). Social-ecological systems exhibit various dynamics, such as resilience and adaptation, which emphasises that the system's balance is transitory and shaped by adaptive cycles (Holling, 1973). Such systems can remain in equilibrium for a period before experiencing rapid and possibly unexpected changes, resulting in either adaptation, transformation or collapse (Walker et al., 2004; Zanotti et al., 2020)—the outcome depends on the capacity for self-organisation and learning (Berkes et al., 2000; Berkes & Folke, 2002; Tengö & Belfrage, 2004).

Small-scale fisheries exemplify such dynamic social-ecological systems (e.g. Berkes, 2006; Gelcich et al., 2010; Partelow, 2015; Salgueiro-Otero & Ojea, 2020) that can adapt to environmental, economic, technological, sociocultural, demographic and governance changes (e.g. Bennett et al., 2014; Zou & Wei, 2010). In developing nations, rising resource demand, overfishing and marginalisation can make small-scale fisheries particularly vulnerable to changes in each of these conditions (Béné et al., 2016; Nayak et al., 2014; Pauly & Zeller, 2016). Mapping the components and linkages of social-ecological systems around artisanal fisheries is crucial for designing strategies to safeguard the ecological and social processes they depend on. The social-ecological system framework, when applied to fisheries, elucidates the interconnections among its components in relation to the sustainable use of fish stocks, which are considered common-pool resources (Ostrom, 2009). By delineating these interactions, this framework enhances comprehension and facilitates effective management of small-scale fisheries (e.g. Basurto et al., 2013; Cinner et al., 2013).

The social-ecological framework is hierarchical and delineates four social and ecological components: resource system, resource units, governance system and users; each of these first-level components can encompass multiple second-level variables (Ostrom, 2007; Salgueiro-Otero & Ojea, 2020). By integrating historical, quantitative and qualitative information about these components, we can enhance our assessment of how they change over time and then adjust current management practices accordingly (Delgado-Serrano & Ramos, 2015; McGinnis & Ostrom, 2014), thereby providing an initial evaluation of the system's resilience and ability to adapt to environmental and cultural changes. One of the components most susceptible to these changes in small-scale fisheries systems is the main users—the fishers. For example, a key driver of spatiotemporal variation within an artisanal fishery system is the transmission of traditional ecological knowledge about fishery resources across generations of the system's users. These fishers accumulate a rich traditional knowledge through long-term interactions with marine ecosystems and with other fishers (Berkes et al., 2000; Moller et al., 2004). Disruptions to this knowledge, or to its transmission, can shift fishers' perceptions about the status of the natural resources (Maia et al., 2018; Pauly, 2019), ultimately limiting their ability to adapt to environmental changes and opportunities to better understand the dynamics of the ecosystem (Lloret et al., 2018). A prime example of a social-ecological system heavily reliant on the transmission of traditional knowledge is the cultural fishing practice involving cooperation between artisanal net-casting fishers and wild dolphins in southern Brazil (Simões-Lopes et al., 1998, 2016).

The cultural human-dolphin cooperative fishery dates back to at least the mid-19th Century (e.g. Areão, 1949; Zappes et al., 2011). It centres on net-casting fishers learning to interpret dolphins' foraging behaviour for gaining reciprocal benefits (Cantor et al., 2023; Figure 1a). Fishers wait along the lagoon margins for migratory Lebranche mullet schools (Mugil liza) to enter the estuary, while Lahille's bottlenose dolphins (Tursiops truncatus gephyreus) herd these schools and cue the fishers when and where to cast nets (Simões-Lopes et al., 1998). By acting in synchrony, fishers catch most of the school while dolphins can target the trapped fish or the escapees (Cantor et al., 2023; Simões-Lopes et al., 1998). In the long term, dolphins experience higher survival rates (Bezamat et al., 2018; Cantor et al., 2023), while fishers obtain socioeconomic well-being and many other non-material ecosystem services from this cooperative fishery, such as a sense of place, cultural values and strong social relationships (Machado et al., 2019; Santos-Silva et al., 2022). However, recent changes in the resource units of this social-ecological system—declining mullet availability and a turnover in the dolphin population—threaten the persistence of this century-old fishery (Cantor et al., 2023). Changes in the fishers' traditional ecological knowledge, in the fishing community composition, and/or their level of engagement in this tradition could occur in response. To address the persistence of this system, it is crucial to understand (i) the transmission mode of the traditional knowledge required to fish cooperatively with dolphins; and (ii) the economic and social significance of this fishery for local communities.

FIGURE 1

The cultural human-dolphin cooperative fishery in Laguna, Brazil. (a) A typical cooperative interaction between artisanal fishers and wild bottlenose dolphins: dolphins approach the coast herding fish schools and cue where and when fishers should cast their nets, resulting in increased catch. (b) Eight main fishing sites are distributed from the canal connecting to the Atlantic Ocean (red circle) to the inner parts of the lagoon (yellow circles). These sites differ in accessibility: (c) in more restricted sites, located in the inner parts of the lagoon (e.g. Ponta das Pedras), fishers wait for dolphins in moored canoes, while (d) in the more accessible site, at the lagoon canal (Tesoura), fishers wait for dolphins standing in the shallow beach waters (Photos: a and d, M. Cantor; c, A.M.S. Machado).

We first synthesise secondary data from scientific and grey literature to contextualise the cultural human-dolphin cooperative fishery in southern Brazil as a social-ecological system. Then we conduct surveys of the local traditional ecological knowledge among the main users of this system—the artisanal net-casting fishers—to investigate the system's spatiotemporal dynamics. Specifically, we evaluate how users vary in experience, engagement, dependence and learning processes over time and across fishing sites that are more open or more closed to external influences. We tested the overarching hypothesis that accessibility of the fishing site affects whether and how the artisanal fishers' involvement in dolphin-assisted fishing changes over time; specifically, that the accessible site should be more vulnerable to changes than the restricted sites, due to the cultural transmission of skills and economic dependence on this fishery being affected by higher turnover of non-specialist, external fishers. Finally, by integrating scientific, local and traditional knowledge, we discuss the implications of changes in the social-ecological system components for the persistence of this reciprocal human-nature relationship in years to come.

2 MATERIALS AND METHODS

2.1 Framing the social-ecological system

We employed the well-established framework for social-ecological systems (McGinnis & Ostrom, 2014; Ostrom, 2007, 2009) to contextualise the cultural human-dolphin cooperative fishery in southern Brazil. Our approach involved a review of secondary data from peer-reviewed publications and technical reports (including grey literature in the local language) to systematise scientific knowledge about the four first-level core components (or subsystems) of the social-ecological system (Figure 2): resource system (RS), resource units (RU), users (U) and governance system (GS). We also considered some of the associated social, economic and political settings (S) and ecosystems (ECO), and some outcomes (O) and interactions (I) among these components.

FIGURE 2

Summary of the social-ecological system around the cultural human-dolphin cooperative fishery. Following Ostrom's (2007, 2009) framework, the first-level core components provide a foundational understanding of a social-ecological system, by relating how natural resources (RS, RU) and humans (U, GS) interact (I) and produce outcomes (O) that are linked to the broader social, economic, and political settings (S) and related ecosystems (ECO).

2.2 Data sampling: Semi-structured interviews with users of the system

We focused on the main users of this social-ecological system—the artisanal net-casting fishers—to explore their experience, involvement, dependence and learning related to the cultural human-dolphin cooperative fishery. We conducted semi-structured interviews with these fishers during four campaigns between 2005 and 2020. Each interview campaign had specific goals, but all aimed to ask objective questions to (i) investigate the fishers' socioeconomic attributes and participation in this cultural fishery, and (ii) assess their perceptions of changes in this fishery (Supplementary Information: Methods). The first campaign in 2005 included 51 interviews and focused on cooperative fishing dynamics and local institutions (Peterson et al., 2008). The second campaign, conducted between 2008 and 2011, included 38 interviews and focused on fishers' ability to identify individual dolphins (da Rosa et al., 2020). The third campaign in 2014 included 53 interviews and focused on understanding the ecosystem services provided by this fishery (Machado et al., 2019). The fourth campaign, conducted in 2019 and 2020, included 80 interviews and focused on social relationships among fishers (Santos-Silva et al., 2022).

Across all interview campaigns, we collected six second-level variables of the users' component to describe their involvement in the traditional fishery with dolphins: (i) general fishing experience (fishers' age, in years, as a proxy for accumulated fishing practice; e.g. Silvano et al., 2006); (ii) expertise in cooperative fishing with dolphins (in years of practice net-casting with dolphins, at the time of the interview, as a proxy for fishers' ability to understand the dolphins' behaviour and react properly); (iii) frequency of fishing with dolphins (whether year-round or occasionally); (iv) economic dependence, or lack thereof, on the fishery assisted by dolphins; (v) the learning process (individual or social) for acquiring the necessary knowledge for net-casting with dolphins; and (vi) the cultural transmission mode (vertical or not) of such traditional knowledge. Individual learning refers to fishers acquiring the tactic through trial and error (self-practice and insight), whereas social learning refers to fishers learning by observing or interacting with other fishers (copying their behaviour or emulating their outcome) (Boyd & Richerson, 1988; Heyes, 1994). Regarding cultural transmission mode, vertical transmission refers to knowledge passed from (grand)parents to their (grand)children; horizontal transmission to knowledge passed among peers of the same generation; and oblique transmission, among unrelated individuals of different generations (Cavalli-Sforza & Feldman, 1981).

Participants were selected by combining snowball and purposive sampling methods (Bernard, 2006), including artisanal fishers who practised dolphin-assisted fishing, and purposive sampling fishers meeting the same criteria at the fishing sites. All selected participants provided previous informed consent and were individually interviewed using semi-structured questionnaires with closed- and open-ended questions. These interviews were conducted at eight primary cooperative fishing sites (Figure 1b): some were more restricted, located in the inner part of the lagoon, and less accessible to external fishers (Figure 1c), while others were more accessible, in the lagoon canal, and more open to external fishers (Figure 1d). One such accessible site is the Tesoura beach, locally regarded as the primary fishing site for cooperative fishing with dolphins (Cantor et al., 2018; Peterson et al., 2008).

2.3 Variation in user involvement across time and space

We built generalised linear mixed models (GLMMs; Bolker et al., 2009) to investigate changes in the involvement of fishers in the social-ecological system across time and space. We tested our hypothesis that the users' involvement in this cultural fishery varies over time depending on the accessibility of the fishing site. We modelled each of the six fisher's self-reported aspects of involvement—fishing experience, expertise, frequency, dependence, learning and transmission mode—as functions of time (as a category defined by the year of the interview campaign) in interaction with the fishing site type, taking the individual fisher identification as a random effect for the intercept to address data overdispersion (Bolker et al., 2009). Our prediction was that users of the more open fishing site would experience more pronounced changes than those of the more closed sites due to higher exposure to external influences. We used a negative binomial error distribution with a log link function for the models on count data, and a binomial error distribution with a logit link function otherwise. Model validation was inspected according to established protocols (Bolker et al., 2009) and using simulated residuals (Hartig, 2020). All analyses were conducted in R (R Core Team, 2022).

2.4 Ethics and consent statement

All people interviewed signed a free informed consent to participate in this research and were interviewed individually. This study was approved by the ethics committee at Universidade Federal de Santa Catarina, Brazil (CEPSH 06457419.6.0000.0121). All personal data were de-identified.

3 RESULTS

3.1 The social-ecological system around human-dolphin cooperative fishery

1. Social, economic and political settings (Figure 2, S): This social-ecological system around the cultural human-dolphin cooperative fishery (Figure 1a) is situated in Laguna, southern Brazil (Figure 1b). Fishing and marine resource gathering in this region date back to pre-Columbian times (Lacerda, 2003), as evidenced by shell mounds (sambaquis; Cadorin, 2013). After European colonisation in the 17th Century, the arrival of Azorean immigrants in the 18th Century stimulated many to transition from farming to fishing (Oliveira, 2011); ever since, the local artisanal fisheries thrived and remained as a vital economic activity. Nowadays, Laguna is home to ca. 46,400 residents; with a Human Development Index of 0.752, Laguna ranks 95th out of 293 municipalities in the state of Santa Catarina and 508th out of 5565 Brazilian municipalities (IBGE, 2020). The average monthly wage is 1.9 times the Brazilian minimum wage, with 17.3% of Laguna's population employed (IBGE, 2020). Politically, the municipality of Laguna shifted from centre-left (2001–2004) and left-wing (2005–2012) to centre (2013–2020) and far right-wing (2021–present) representation, aligning with Brazil's federal political swings over the past two decades.
2. Resource system (Figure 2, RS): The human-dolphin cooperative fishery unfolds within a 300 km² complex lagoon system, encompassing Mirim, Imaruí and Santo Antônio lagoons, the Tubarão River outfall and the canal linking the system to the sea (Figure 1b). Artisanal fishing, which is crucial for the local economy and culture, employs various techniques including net-casting, angling, manual trawling, fyke (fixed fish traps for shrimp), stake (fixed fish traps for fish) and trammel netting (two or three layers of nets kept vertical in the bottom of the lagoon; FAO, 1990). The unique cooperative fishing between net-casting fishers and dolphins (Figure 1a) occurs regularly at least eight cooperative fishing sites (Figure 1b; Peterson et al., 2008). The main fishing site is Tesoura, a beach in the canal connecting the lagoons to the ocean (Cantor et al., 2023; Simões-Lopes et al., 1998); the other sites are in the inner parts of the lagoon (Areial, Iate Clube, Ponta das Pedras, Arrebentão, Toca da Bruxa, Balsa and Rio Tubarão).

3. Resource units (Figure 2, RU): In this cultural fishery, primary resources are fish and dolphins. The Lebranche mullet is a key resource for both industrial and small-scale fisheries in southern Brazil (Machado et al., 2021; Sant’Ana et al., 2017), particularly targeted in the cultural human-dolphin cooperative fishery, especially during their reproductive migration between April and July (Herbst & Hanazaki, 2014; Simões-Lopes et al., 1998). Laguna artisanal fisheries contributed to about 10% of Santa Catarina's total mullet catch between 2003 and 2012 (850 tons; UNIVALI/EMCT/LEMA, 2020). In 2012, the human-dolphin cooperative fishery at Tesoura beach (Figure 1b) alone accounted for ca. 13 tons of mullet (Monteiro et al., 2014). However, the regional mullet stock is now considered overexploited (Sant'Ana et al., 2017) and exhibits potential early signs of decline (Cantor et al., 2023). Boat-based surveys over three decades indicate the resident dolphin population remains relatively small (55–60 individuals; Daura-Jorge et al., 2013), with no apparent trends in population size (Cantor et al., 2023). Further, dolphins that frequently cooperate with fishers exhibit smaller home ranges (Cantor et al., 2018) and higher survival rates (Bezamat et al., 2018) despite similar reproductive success (Bezamat et al., 2020). This dolphin population faces various threats, including accidental bycatch in illegal fishing gear (Bezamat et al., 2021), habitat loss (Agrelo et al., 2019), chemical pollution (Righetti et al., 2019), vessel traffic and noise pollution (Pellegrini et al., 2021).
4. Users (Figure 2, U): The main users of this system are the artisanal fishers who cast nets with the dolphins' assistance. Laguna officially registers nearly 4300 fishers, although the exact number engaging in the cultural human-dolphin cooperative fishery remains unclear. These fishers can be professionals (formally registered, relying on artisanal fishing as a primary income source), opportunistic (not formally registered, engaging in dolphin-assisted fishing to supplement their income) or amateurs (not formally registered, using dolphin-assisted fishing as a recreational activity) (Catão & Barbosa, 2018; Machado et al., 2019). Some are locals (from Laguna), while others are external users (often opportunistic or amateur fishers) labelled as ‘outsiders’ or ‘tourists’ by the locals (Peterson et al., 2008). Fishers who do not depend on fishing are often retirees or have other primary occupations (e.g. painters, security guards and policemen). These fishers distribute themselves across the eight cooperative fishing sites that are more open or closed to external influence (Figure 1b). The high accessibility by foot or car of the main site in the lagoon canal, Tesoura beach (Figure 1d), makes it a fishing site open to any fisher. This site attracts a mix of professionals, opportunistic and amateur fishers, both locals and outsiders (Machado et al., 2019). These users differ in experience, dependence and motivation for fishing (Catão & Barbosa, 2018; Santos-Silva et al., 2022; Valle-Pereira et al., 2022). The remaining sites are all situated in the inner parts of the lagoon and accessible only by boat or through small neighbourhoods (Figure 1c). The restricted access makes these fishing sites more closed to opportunistic and amateur outsiders, with higher excludability, and they are often used by local professional fishers (Peterson et al., 2008).
5. Governance system (Figure 2, GS): The governance system encompasses formal and informal rules, laws and institutions that shape the management of the cultural human-dolphin cooperative fishery. Although formal fishing regulations exist, such as the Federal Law 11.959/2009 regulating fishing activities in Brazil, enforcement in Laguna is inconsistent. This situation tolerates anyone with a cast net to engage in dolphin-assisted fishing, thereby favouring the presence of outsiders. Local fishers perceive outsiders as competitors (Machado et al., 2019), leading to occasional disagreement even involving local fishers who are not economically dependent on fishing (Peterson et al., 2008). To mitigate these conflicts, local fishers have established their own informal operational rules, which can differ between fishing sites (Peterson et al., 2008). These informal rules define the number and location of fishing spots within a site, the order of access to spots, time limits per spot and fishing quotas. For instance, at the open fishing site, the accessible Tesoura beach, fishers must vacate their spot for another fisher waiting in line whenever they catch more than one fish, regardless of size (Peterson et al., 2008). Instead of waiting for a spot, fishers can stand right next to a spot, but they are only allowed to cast after the fisher occupying the spot has cast first; alternatively, fishers can form collaborative groups, rotate their spots and equally share their daily gains (Peterson et al., 2008; Santos-Silva et al., 2022). Enforcement of these rules for outsiders is lenient, as long as they adhere to the informal guidelines. By contrast, at more restricted fishing sites, such as Rio Tubarão, Ponta das Pedras and Toca da Bruxa, fishers use a shift rotation system. There, fishers occupy spots in order of arrival, enabling each fisher to cast their net three times before shifting spots. Frequently, related fishers collaborate, alternating between resting on the boat and actively net casting (Peterson et al., 2008).

Beyond the informal rules, recent legislative developments at municipal and state levels aim to safeguard both dolphins and the traditional fishery due to their ecological, economic and cultural significance. Since 2018, the Laguna Municipal Law 033/2018 protects the dolphin population by prohibiting fishing gear that could cause accidental bycatch, such as gill and trammel nets. A State Law designates 25 May as the Day for the Preservation of Dolphins that Fish with Humans, promoting awareness of the practice's local cultural and economic importance. Nationally, there are ongoing proposals to recognise the human-dolphin cooperative fishery as a Natural and Intangible Cultural Heritage. Local non-governmental institutions also contribute through educational initiatives to promote public awareness, sustainable tourism, and conservation research.

6. Interactions and outcomes (Figure 2, I and O): Interactions between components, focused on the users, are exemplified by the different levels of harvesting (U-RU), potential conflicts (U-GS), rules (U-GS), dynamic shifts between cast net fishing with dolphins and the use of other fishing gears, targeting other species (U-RS). The public awareness about the dolphin-fisher interaction is an outcome of this social-ecological system; however, it can attract more amateur fishers thereby increasing potential conflicts. More broadly, overexploitation of the Lebranche mullet, either by the industrial or small-scale fisheries, can jeopardise the sustainability of the system.
7. Related ecosystems (Figure 2, ECO): Related ecosystems encompass adjacent subtropical estuarine and lagoon systems in southern Brazil. These ecosystems are interconnected through abiotic and oceanographic conditions, and through the regular reproductive migration of mullet schools flowing into and out of these estuaries and lagoons (Herbst & Hanazaki, 2014; Lemos et al., 2016). Although this is a rare occurrence, dolphins from resident populations can occasionally disperse between these ecosystems (Costa et al., 2015; Simões-Lopes & Fabian, 1999). As in Laguna, the related ecosystems face increasing acoustic and chemical pollution resulting from anthropogenic activities, potentially affecting dolphins, humans and their prey (e.g. Ferreira et al., 2021; Pellegrini et al., 2021; Righetti et al., 2019).

3.2 Spatiotemporal variation in the users of the social-ecological system

Having mapped the social-ecological system around cultural dolphin-assisted fishing, we now investigate the main users of this system more closely. Specifically, we consider how the six second-level variables describing the involvement of the artisanal fishers in this cultural practice may vary over time and across fishing sites. Between 2005 and 2020, we conducted 222 interviews (2005 campaign: 51; 2008–2011: 38; 2014: 53; 2019–2020: 80 interviews) with 188 individual artisanal fishers who net-cast with dolphins. All fishers were male, middle-aged (mean ± SD, 48.58 ± 14.48 years) and had on average almost three decades of experience in net-casting with dolphins (mean ± SD, 28.15 ± 15.31 years). Most fishers (76.5%) reported engaging in net-casting with dolphins year-round, and over half (57.8%) relying partially or entirely on this fishery for their livelihood. Most fishers (82.7%) acquired the necessary knowledge for net-casting with dolphins through social learning, with over half (56.8%) learning vertically, from their parents or grandparents. Twenty-six fishers were interviewed multiple times: 18 in two campaigns and eight in three campaigns. In their first interviews, 20 out of these 26 fishers (77%) reported fishing as their primary source of income; in their last interviews, five of those 26 fishers (19%) reported no longer being economically dependent on artisanal fishing. No changes in the opposite direction were reported, suggesting a unidirectional trend towards reduced economic dependence on this particular fishing practice over time.

Fishers' socioeconomic attributes fluctuated across the interview campaigns and between accessible and restricted fishing sites that are more open or closed to external fishers. Interview data suggested that while fishers using both sites generally had similar levels of fishing experience (Figure 3a,b), those using more restricted sites tended to engage in year-round fishing (Figure 3c) and were more often economically dependent on dolphin-assisted fishing (Figure 3d) compared to those using the accessible site. Additionally, there was a slight tendency for higher incidence of vertical social learning among fishers using the sites more closed to external fishers (Figure 3e,f); however, this tendency has reduced in recent interview campaigns. It is worth noting that some of these spatial and temporal patterns have been previously identified in single interview campaigns (da Rosa et al., 2020; Machado et al., 2019; Peterson et al., 2008; Santos-Silva et al., 2022). Nevertheless, the current analyses of the integrative interview data revealed that only a few of these relationships achieved statistical significance (Figure 4; Tables S1–S6). Interview data can be complex and variable, which may have limited the statistical power to detect these patterns quantitatively; therefore, we acknowledge their qualitative relevance and discuss these observed trends despite the lack of statistical significance.

FIGURE 3

Attributes of the main users of the social-ecological system over time and space. Variation in artisanal fishers who cooperate with dolphins across interview campaigns and fishing site type (canal: accessible site more open to external fishers; lagoon: restricted sites more closed to external fishers). (a) General fishing experience (accumulated fishing practice, proxied by fishers' age in years, n = 222 interviews); (b) expertise in cooperative fishing (in years net-casting with dolphins, n = 215 interviews); (c) fishing frequency as the proportion of fishers engaging in dolphin-assisted fishing year-round (purple) or only in the mullet season (green) (n = 217 interviews); (d) economic dependence (purple) or not (green) on dolphin-assisted fishing (n = 220 interviews); (e) learning category of the traditional knowledge of how to cooperate with dolphins, as individual (purple) or social learning (green) (n = 151 interviews); (f) cultural transmission mode of this knowledge as vertical (green) or other (individual, horizontal, oblique) learning process (purple) (n = 151 interviews).

FIGURE 4

Relationships between attributes of main users of the social-ecological system over time and space. GLMM predictions of how artisanal fishers' attributes varied over interview campaigns and types of fishing site (canal: accessible site more open to external fishers; lagoon: restricted sites more closed to external fishers): (a) General fishing experience in terms of accumulated practice, proxied by fishers' age; (b) cooperative fishing expertise, in years net-casting with dolphins; and the proportion of fishers who (c) depend economically on dolphin-assisted fishing, (d) engage on dolphin-assisted fishing year-round, (e) socially learned the traditional ecological knowledge required to cooperate with dolphins and (f) acquired this knowledge via vertical cultural transmission. Gaps represent missing data.

General fishing experience, in terms of accumulated practice and proxied by age (Figure 4a; Marginal R² = 0.065), increased in the second (2008–2011: β = 0.213, SE = 0.010, p = 0.03909; Table S1) and fourth interview campaign (2019–2020: β = 0.200, SE = 0.074, p = 0.00669; Table S1) when compared to the first campaign (2005), regardless of the fishing site. On the other hand, experience in net-casting with dolphins (Figure 4b, Marginal R² = 0.015) did not vary over time, with no clear differences between more accessible and more restricted fishing sites (Table S2). Fisher's economic dependence on dolphin-assisted fishing, although did not vary significantly between campaigns and fishing sites, had a subtle reduction in the more accessible site (Figure 4c; Marginal R² = 0.242; Table S3). The frequency of engagement in dolphin-assisted fishing also showed no distinct trend over time (Figure 4d; Marginal R² = 0.285), with only a subtle increase in both types of fishing sites in the third interview campaign (2014: β = 2.38, SE = 1.24, p = 0.056; Table S4). Social learning of the techniques required for cooperation with dolphins was widespread but also did not vary between campaigns and fishing sites (Figure 4e; Marginal R² = 0.012; Table S5). However, the process of learning via vertical transmission seems to be more frequent in the more restricted fishing sites (Figure 4f; Marginal R² = 0.066; Table S6). All models were validated and met most of the premises (Figures S1–S6); however, model fit was generally low, meaning that the proportion of the variance explained by temporal (interview campaigns) and spatial (more or less accessible fishing sites) factors was low, suggesting there is considerable variation in the data that remains unexplained by the fishers' attributes assessed.

Finally, over the past decades, the transmission among the system's users of the traditional knowledge required to fish with dolphins has involved a mix of individual learning and horizontal, oblique and vertical social learning (Figure 5). The proportion of reported vertical learning has apparently decreased recently (Figure 5a), particularly among fishers who use the site more open to external influence (Figure 5b).

FIGURE 5

Variation in the mode of cultural transmission of the traditional knowledge involved in the human-dolphin cooperative fishery. Mode of transmission of the techniques required to cooperate with wild dolphins as reported by artisanal net-casting fishers, according to (a) the decade when they began fishing (n = 133) and (b) the type of fishing sites (n = 151) they use (canal: accessible site more open to external fishers; lagoon: restricted sites more closed to external fishers). Neither time nor space statistically explained this variation (Table S6). The decade of learning was estimated based on the fishers' age and the number of years they reported practising net-casting with dolphins.

4 DISCUSSION

For over a century, the human-dolphin cooperative fishing in southern Brazil has persisted across multiple generations of artisanal net-casting fishers and wild dolphins likely through the reciprocal benefits they accrue from this tradition. After mapping the social-ecological system around this cultural practice, we now reflect how the main users of this system and the transmission of their traditional ecological knowledge vary over time and space and examine the implications of these variations for the resilience of the social-ecological system.

4.1 Variation and stability in the social-ecological system

The main users of the social-ecological system around the cultural human-dolphin cooperative fishery are distributed in several fishing sites, each differing in its susceptibility to external influences (Peterson et al., 2008). Our investigation of socioeconomic attributes of these users reveals that time and fishing site account for some—though not all—of the observed variation. First, the age structure and the users' overall experience in fishing, including net-casting with dolphins, have remained relatively stable over the past 16 years. The lack of significant differences in fishing experience between more open and more closed fishing sites is intriguing, particularly considering the accessibility of the former to amateur outsider fishers (Machado et al., 2019; Peterson et al., 2008). The similar overall fishing experience between the fishers who use the two types of sites can be attributed to the influx of less experienced fishers in the accessible site, which offsets the accumulation of experience over time (in terms of increased performance) of the recurring fishers. In fact, recent drone-based tracking of net-casting behaviour revealed variations in daily performance among individual fishers—experienced fishers who understand the dolphins' cues and react promptly by casting larger nets closer to the dolphins have higher success rates than novices (Valle-Pereira et al., 2022). This suggests that self-reported years of fishing experience may not fully capture the nuanced individual-level factors that determine the expertise required to succeed in this traditional fishery. In other words, while experienced fishers improve their performance, new fishers with lower performance would generate variation in performance between fishers and would maintain an average fishing performance over time.

The frequency at which artisanal fishers engage in dolphin-assisted fishing has fluctuated over the years but has generally remained high. Despite the apparent decline in the mullet availability nearshore and in the number of dolphins involved in this fishery (Cantor et al., 2023), our survey indicates that most fishers in both accessible and restrictive fishing sites continue to cooperate with dolphins year-round. The increased industrial fishing during the mullet reproductive migration suggests overexploitation of the regional stock in southern Brazil (Gonzáles-Castro et al., 2015; Sant'Ana et al., 2017). However, given that artisanal fishers tend to be aware of fish stock status (e.g. Martins et al., 2018), their consistent willingness to keep fishing with dolphins could suggest that local mullet availability has not yet been perceived as critically low. Continued monitoring of traditional knowledge will be necessary for detecting early signs of changes in the resource system at local scales (e.g. Hopping et al., 2016; Lauer & Aswani, 2010). However, as in many fisheries-dependent communities (e.g. Charles et al., 2012; Salmi & Salmi, 2005), not all users of this system fish only for subsistence; cultural identity and a sense of belonging also motivate them (Machado et al., 2019; Santos-Silva et al., 2022). These nonmaterial benefits could also sustain the fishers' engagement in dolphin-assisted fishing even during less profitable times, potentially masking the underlying low resource availability.

Indeed, our interviews suggest that economic dependence on the cultural human-dolphin cooperative fishery has fluctuated over the years, across communities. Fishers utilising the restrictive sites within the lagoon tend to rely on this traditional practice for subsistence and family income (Peterson et al., 2008). In contrast, fishers using the accessible fishing site have more diverse motivations for fishing with dolphins—many rely on other jobs or sources of income and cooperate with dolphins as a recreational, social activity (Machado et al., 2019; Santos-Silva et al., 2022)—which can reflect the socioeconomic disparities among fishers who use more and less accessible fishing sites. For instance, the fishing site at Ponta das Pedras is in a traditional neighbourhood where families share their catch with relatives and friends but sell the fish to retailers via a middleperson (Machado et al., 2019). Despite the more reliable sale, such intermediaries impose a much lower market price on the mullet (ca. USD$0.75/kg) compared to the premium price (ca. USD$10/kg) that fishers at the accessible fishing site can get by selling directly to consumers who have the opportunity to observe the cooperative fishing with dolphins in action (Machado et al., 2019). The accessibility of this fishing site at the lagoon canal adds value to the fishing resource and indirectly contributes to the local economy by reinforcing the touristic appeal of the cultural human-dolphin cooperative fishery.

In turn, the accessible fishing site makes it open to both professionals and amateurs, thereby fostering a more competitive environment than the restrictive sites within the lagoon. While competition can lead to cooperation—fishers can form groups based on trust and reciprocity to share tasks and outcomes (Peterson et al., 2008; Santos-Silva et al., 2022)—it can also lead to conflicts, as seen in other artisanal fishing systems (Andrade & Schiavetti, 2015; Fratsea & Papadopoulos, 2022). Fishers who use the secluded sites within the lagoon avoid the crowded and accessible lagoon canal, complaining that those who do not depend economically on dolphin-assisted fishing monopolise such a prime fishing site (Peterson et al., 2008). The governance system has improved recently, with the increasing presence of governmental and non-governmental institutions interested in implementing legal instruments, monitoring, and raising public awareness to safeguard this cultural practice. However, this also increased the popularity of dolphin-assisted fishing, attracting more amateur fishers and hobbyists to the accessible site and so fuelling conflicts with local professional fishers from the lagoon. Participatory processes to bring together these different stakeholders can help mitigate these conflicts, build effective and nested governance structures, and promote adherence to principles of social-ecological sustainability (Begossi, 2006; Trimble & Berkes, 2015). Enhancing trust and communication between artisanal fishers and these institutions is crucial for effective community-based conservation of the social-ecological system (Ostrom, 1990).

4.2 Transmission of traditional knowledge and the persistence of the social-ecological system

The persistence of this traditional fishery relies on how artisanal fishers acquire and transmit the ecological knowledge required to cooperate with wild dolphins (da Rosa et al., 2020; van der Wal et al., 2022). Understanding the local conditions that influence fish availability and dolphin behaviour (Peterson et al., 2008), recognising individual cooperative dolphins (da Rosa et al., 2020), and reacting to their cues by casting nets appropriately (Valle-Pereira et al., 2022) are all critical elements of the traditional knowledge that ensure the human-dolphin foraging synchrony, crucial for their short- and long-term benefits (Cantor et al., 2023). Thus, this shared understanding of each predator's role in their changing environment is fundamental for the success of the reciprocal relationship between humans and dolphins, and thus for its long-term viability and persistence (van der Wal et al., 2022).

Interviews provide invaluable insights on how users of the social-ecological system acquire and transmit their traditional knowledge. Most artisanal fishers report learning the practice socially, by observing and then imitating the behaviour or emulating the outcome of other fishers; a few reported learning the technique individually, by trial and error. The mode of cultural transmission varies, with an apparent tendency for vertical transmission to be more common at fishing sites that are more restricted to external influences. In these closed communities, fishers typically have learned vertically or obliquely, from (grand)parents or relatives of different generations, potentially due to the physical and social restrictions that tend to exclude external fishers. By contrast, the more open fishing site favours horizontal learning, between unrelated individuals of the same generation (see Cantor & Whitehead, 2013), because the accessibility of the beach at the lagoon canal creates a socially interactive context where fishers from different generations, families and backgrounds can constantly interact (Santos-Silva et al., 2022).

The transmission of traditional ecological knowledge can adapt to social and environmental changes (e.g. Gómez-Baggethun et al., 2013), and the mode of knowledge transmission in the human-dolphin cooperative fishery has fluctuated over the past decades, with a general shift away from vertical and oblique learning. Contributing factors include reduced interest among younger generations due to limited profitability and low status associated with artisanal fishing (e.g. Blythe et al., 2013; Power et al., 2014). This trend can be reinforced by relatives who actively encourage the new generation to explore alternative career paths. In addition, horizontal learning can be facilitated by online resources that make the dolphin-fisher cooperation accessible to wider audiences, further exposing the traditional knowledge on how to fish with dolphins to external influence, therefore rapid changes. For instance, social media and video sharing platforms can attract external, and inherently less experienced fishers to interact with dolphins, potentially accelerating changes in this system. Partially in consequence, our study suggests that the cultural human-dolphin cooperative fishery may be shifting from subsistence activity to a recreational hobby, as previously seen at the more accessible site (Machado et al., 2019) where excludability of external users of this social-ecological system is unlikely.

While traditional ecological knowledge may be adapting to current conditions, such changes may not be adaptive in the evolutionary sense (Fernández-Llamazares et al., 2015). The shift from vertical learning to more diffuse transmission could impact the characteristics of the cultural human-dolphin cooperative fishery in the long term. Vertical transmission tends to result in more accurate knowledge transfer, whereas open learning processes may introduce errors and maladaptive behavioural variants (Cantor & Whitehead, 2013). Complex behaviours—such as those required for fishing with dolphins effectively (da Rosa et al., 2020; Valle-Pereira et al., 2022)—are more accurately transmitted through strong and long-lasting bonds, such as parent-child relationships (Cantor & Whitehead, 2013; McElreath & Strimling, 2008). A case in point highlighting the importance of a close relationship between learners and mentors is that artisanal fishers who learned from their fathers how to cooperate with dolphins are better at identifying cooperative dolphins than fishers who learned individually or from their peers (da Rosa et al., 2020). Disrupted knowledge transmission could hinder the fine-scale synchrony between dolphins' actions and fishers' reactions that is crucial for their mutual success (Cantor et al., 2023) with unpredictable downstream consequences in the social-ecological system. Maintaining the cultural human-dolphin cooperative fishery and its associated rules, norms, and regulations (Peterson et al., 2008) is essential for safeguarding the reciprocal contributions that both species accrue, thereby ensuring the long-term viability of this social-ecological system (van der Wal et al., 2022). However, there is a trade-off in preserving tradition and adapting to changes.

Adaptive measures should also seek to balance the maintenance of the traditional knowledge with the evolving social context experienced by the fishing community dependent on this cultural practice. Strengthening spaces and forums where the various stakeholders can discuss public policies on artisanal fishing, specifically cooperative fishing, can foster the creation of trust bonds between fishers of different generations and facilitate the transmission of knowledge between them. While it may not be possible to guarantee learning through vertical transmission, which involves kinship ties, it is possible to strengthen oblique transmission by fostering greater interaction and trust between older and younger fishers. When considering the resilience of these social-ecological systems, maintaining more conservative modes of transmission of traditional knowledge (vertical and oblique) and promoting interaction between fishers and dolphins can contribute to the adaptability of the system rather than its transformation or collapse. Adaptability is often characterised as incremental change that allows a system to maintain its domain and trajectory, whereas transformation typically implies a more abrupt change, potentially resulting in the emergence of a new system (Walker et al., 2004; Zanotti et al., 2020).

4.3 Closing remarks

Our study underscores the continued historical use of the cultural fishing involving Local Communities of artisanal fishers and wild dolphins, while also highlights changes in a fundamental component of the associated social-ecological system—the artisanal fishers, as the main users of this system. Preserving compatible interspecific knowledge regarding cooperation between humans and wildlife is crucial for safeguarding their social-ecological systems (van der Wal et al., 2022), but it is equally important to protect the resource system and resource units—a suitable environment and healthy populations of mullet, dolphins, and artisanal fishers. Therefore, future efforts aiming to safeguard this system should prioritise strengthening governance mechanisms, building trust among stakeholders and maintaining the fine-scale synchrony between dolphins and fishers that underpins the success of this remarkable cultural practice.

These research and safeguarding endeavours should explicitly involve the main users of the system and strike a balance between preserving their traditional knowledge on how to fish with dolphins and adapting to the emerging challenges in the dolphin's and fisher's communities. Bridging traditional ecological knowledge with scientific research can build trust within the governance institutions (Folke et al., 2005), and empower Indigenous Peoples and Local Communities as stewards of natural resources. Engaging fishers and their deep knowledge about their social-ecological system in public forums for the sustainability of artisanal fisheries will be invaluable to enhance the resilience of this cultural heritage, thereby preserving its reciprocal contributions to humans and dolphins for generations to come. The current evidence indicates that this cultural fishery is reciprocally beneficial for dolphins and humans, in terms of foraging outcomes, cultural belonging and socioeconomic well-being for fishers (Peterson et al., 2008; Santos-Silva et al., 2022; Simões-Lopes et al., 1998), while also contributing to the long-term survival for dolphins (Bezamat et al., 2018; Cantor et al., 2023). Continued research efforts will likely reveal the broader consequences of this human-wildlife interaction beyond the population and community levels, but also for the local ecosystem.

AUTHOR CONTRIBUTIONS

Bruna Santos-Silva, Natalia Hanazaki and Mauricio Cantor conceived the idea; Natalia Hanazaki, Mauricio Cantor, Bruna Santos-Silva, Débora Peterson, Alexandre M.S. Machado, Daiane X. da-Rosa, Fábio G. Daura-Jorge and Paulo C. Simões-Lopes designed methodology; Bruna Santos-Silva, Alexandre M.S. Machado, Daiane X. da-Rosa and Débora Peterson collected and processed the data; Mauricio Cantor, Fábio G. Daura-Jorge and Natalia Hanazaki analysed the data; Mauricio Cantor, Natalia Hanazaki, Fábio G. Daura-Jorge and Paulo C. Simões-Lopes provided supervision and funding; Mauricio Cantor led the writing of the manuscript with main contributions from Bruna Santos-Silva and Natalia Hanazaki; Mauricio Cantor, Fábio G. Daura-Jorge, Natalia Hanazaki and Sofia Zank led the revision of the manuscript. All authors contributed critically to the argument and interpretation, agreed to be accountable for the manuscript and approved its submission for publication.

ACKNOWLEDGEMENTS

We are deeply grateful to the fishers for their collaboration over the years. We thank the researchers who helped with data sampling and field logistics across interview campaigns, and the anonymous reviewers for their invaluable suggestions.

FUNDING INFORMATION

This study is part of the Long-Term Ecological Research Program ‘Sistema Estuarino e Adjacências’ (PELD-SELA, peldsela.com.br) supported by the Conselho Nacional de Pesquisa e Desenvolvimento Tecnológico (CNPq 445301/2020-1) and Fundação de Amparo à Pesquisa do Estado de Santa Catarina (FAPESC 2021TR387), with additional funding of the Brazil-Germany PROBRAL Research Program funded jointly by CAPES and the Deutscher Akademischer Austauschdienst (CAPES-DAAD 23038.002643/2018–01), and from the National Geographic Society (WW201R-17, NGS-101549R-23). M.C. was supported by CAPES (88881.170254/2018-01), the Department for the Ecology of Animal Societies at the Max Planck Institute of Animal Behavior, and the Oregon State University's Marine Mammal Research Program Fund, Jungers Faculty Development and Research Fund, Marine Studies Initiative, and College of Agricultural Sciences. B.S.S., A.M.S.M, D.X.d., and J.V.S.V-P received MSc scholarships from CAPES (Finance Code 01); F.G.D.J was supported by CNPq (308867/2019-0) and FAPESC (TR2012000295, 2021TR000581); P.C.S.L. was supported by CNPq (305777/2020-3); N.H. received a research productivity scholarship from CNPq (305789/2022-1).

CONFLICT OF INTEREST STATEMENT

The authors declare no competing interests and that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

STATEMENT ON INCLUSION

Our study brings together authors from different genders and career stages (graduate students, early-career researchers, and established professionals), all of whom were born, raised and trained in the country where the study was carried out. All authors were engaged with the data sampling, methodology and interpretation of results to encompass their diverse perspectives. There were active efforts to cite the literature published by scientists from the region, including relevant work published in the local language.

POSITIONALITY STATEMENT

The authors of the study are biologists and academics in the fields of population, behavioural and human ecology, and ethnobiology, who have long empirical experience (between ca. 3 and >35 years) working with the social-ecological system around the dolphin-fisher cooperative fisheries in Laguna, southern Brazil. However, none of the authors are active participants in this system as they do not depend, economically or otherwise, on it; all authors share cultural aspects with the main users of the system (artisanal fishers) but can be socioeconomically distinguished from them. As such, the authors identify themselves as external observers whose understanding of this social-ecological system may be functional simplifications that are unintentionally influenced by their own worldviews, privileges, academic and personal trajectories.

Open Research

DATA AVAILABILITY STATEMENT

The anonymised data and R code associated with this study is deposited at the Zenodo repository: https://doi.org/10.5281/zenodo.11377388.