Historically, humans have trained many animals to help them to find food: examples are dogs, falcons, and cormorants. Several of these species are domesticated or have behavioral traits that could be targeted for artificial selection in a process where both species benefit [1]. Human-animal interactions with mutual benefits in the wild, however, are much rarer. Moreover, the costs and benefits involved for both parties are not always fully understood, being in the agenda of a multidisciplinary debate on the nature of such interactions (for a semiotic perspective on human-animal interactions, see [2]). Among the many examples of human and animal interactions, a fascinating case is the interaction between people in Mozambique and Tanzania and a species of wax-eating bird, called the greater honeyguide (Indicator indicator). Human hunters and birds work together to access bees’ nests and honey—honey for hunters, beeswax for birds [3, 4]. Such positive interactions seem to be decisive for the evolution of those involved. For instance, the interactions that humans have kept for millennia with scavengers such as vultures, hyenas, and lions, have been crucial in the evolution and welfare of humankind [5]. Nevertheless, this kind of positive interaction becomes complicated when on the non-human side there is a species of high cognitive and social abilities [6, 7]. Cognition comprises processes such as perception, attention, action, and memory, to cite a few [8]. For a positive interaction such as cooperation to happen, perception and memory can aid tracking reciprocity, allowing individuals to weigh the pros and cons involved [9].
Positive interactions between humans and animals also extend to the marine environment—fishers and cetaceans have been historically reported to interact worldwide. One of the first reports was done by the Roman naturalist Pliny the Elder (A.D. 32–79), who described a cooperative hunt between fishers and dolphins during the mullet season in southern France circa 70 A.D. [10]. Fishers used to call dolphins that herded mullet schools into positions where fishnets could be easily placed; dolphins apparently caught some of the fish as well. A similar case was reported for Aborigines and dolphins in Moreton Bay, Australia [11]. There, fishers used to make a peculiar splash in the water in attempt to signalize for dolphins the location of the fish—again, mullets—which were herded toward the shore by the dolphins. For these oldest two cases, dolphins’ species were not identified, but both involved mullets as the shared resource. Dolphins and indigenous people cooperation were also reported among the Imragen people of Mauritania, Africa [12]; as well as for Irrawaddy River dolphins in Burma [13], Amazon River dolphin in Brazil [14], and River dolphins in India and China [15]. Although the behavioral and ecological nature of all these interactions are poorly known, the benefits involved seem to be mutual, requiring that both humans and dolphins synchronize and understand each other’s behavior to access and share the same prey.
More insights into benefits, synchrony, and communication in human-animal interactions come from an intensely studied case of artisanal net-casting fishers and bottlenose dolphins (Tursiops truncatus gephyreus) in southern Brazil. In Laguna, there is a resident population of bottlenose dolphins (~ 60 individuals) [16], in which some individuals specialized in foraging with net-casting artisanal fishers [17]. Dolphins herd mullet schools toward a fishers’ barrier on the shore awaiting a “stereotyped” behavioral cue by the dolphins—tail slap, head slap, back presentation, or partial emersion [18]. Such cues are understood by the fishers as the right moment to cast their nets. Fishers benefit from this interaction by catching more fish when the dolphins are present and, supposedly, dolphins accrue similar benefits [17]. For the dolphin population, the interaction has further implications, influencing spatial distribution [19], social behavior [20], acoustic behavior [21], and population dynamics [16].
Although it remains poorly understood how this interaction alters fishers’ behavior, it is clear that fishers perceive and rely on the dolphins’ behavior. They synchronize their actions with the dolphins’ actions [17] and reported at least nine ecosystem services from this interaction, including provision, cultural, and social benefits [22]. Interestingly, fishers also report being able to identify dolphins, classifying them as “good” dolphins—those that often interact with them, and “bad” dolphins—those that do not [23]. Fishers, therefore, seem to have valuable knowledge on dolphins’ life-traits and commonly share anecdotes and curiosities about many ecological and behavioral aspects of dolphins at the individual level. Curiously, fishers attribute celebrities names to dolphins—e.g., football players, movie actors, politicians—demonstrating a high level of familiarity.
A long-term study has been monitoring this dolphin population and their interaction with fishers. Long-term studies on population ecology and behavior, however, are money-hungry, time-demanding, and require a systematic effort [24]. Long-term studies are particularly challenging when involving cetaceans, which are wide-ranging, deep-diving, and fast-moving animals [25]. In this context, traditional ecological knowledge can fill some of the gaps of scientific knowledge on the species, habitat, and ecosystems [26,27,28], enabling quick solutions for co-management and immediate conservation of ecological systems [29,30,31].
Fishers’ knowledge of cetaceans usually focuses on the general characteristics of the animals (e.g., [32, 33]). The intricate knowledge fishers seem to have on dolphins in Laguna is then an opportunity to understand how the local knowledge about these animals is built individually. However, the fishing community that interacts with dolphins is very heterogeneous, economically, and socially, as well as in their historical engagement in the interactive tactic [22, 23]. For instance, fishers vary in terms of experience in foraging with dolphins. Fishers also fit into different socio-economic profiles: (a) the professionals—those who rely on the fishing activity as the main source of income; (b) the opportunists—those who tend to interact with dolphins only during the mullet season; (c) and the amateurs—those who engage in the fishing with dolphins all year long, but as a hobby, since their main source of income depends on other activities [22]. The analysis of traditional knowledge needs to account for such variability that likely affects the quality and accuracy of individual perceptions on their systems [22, 28, 34].
Here, we investigate the consensus in individual fishers’ perceptions of individual recognition and naming of dolphins they interact with. If fishers are highly consistent in identifying dolphins, their knowledge could be used to describe individual dolphins’ life-traits, such as sex, behavior, age, and kinship relationships—all of which valuable information that requires long-term, systematic sampling effort to be estimated in the wild. We also investigated the factors that can influence this recognition process. By exploring how fishers can recognize dolphins, we have elements to discuss: (a) to which extent the detailed fishers’ knowledge can be used to complement ecological information on dolphins; (b) how intricate the dolphin-fisher foraging interaction is; (c) and how critical the fishers’ traditions and perceptions of the dolphins’ lives might be for this interaction to persist—a possible requisite for all positive dolphin-human interactions.