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Evolution & Behaviour

The fate of a century-old partnership between humans and dolphins

Aligning human interests and wildlife protection requires a deep understanding of human-wildlife interactions. Behavioral tracking and demographic surveys show that foraging synchrony is key to generate short- and long-term benefits for human fishers and wild dolphins. We used simulations to describe the conditions under which this cooperation can turn into another human-wildlife conflict.

Credits: Carolina Bezamat ©
by Mauricio Cantor | Assistant Professor

Mauricio Cantor is Assistant Professor at Oregon State University.

Mauricio Cantor is also an author of the original article

Edited by

Margaux Héritier

Senior Scientific Editor

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Reading time 4 min
published on Sep 4, 2023
Humans’ interactions with nature have been the key to our global ecological success. But such interactions are typically one-sided—humans gain the largest benefits; nature pays the larger cost—thereby fueling the current global ecological crisis. Compared to the widespread escalating human-wildlife conflicts, interactions that benefit both humans and nature are rare. Striking examples involve cultural practices in which humans cooperate with wild animals, joining their complementary hunting skills to achieve the same goal of catching a bite. However, all historical cases of human-wildlife cooperative hunting—hunters-honeyguides, whalers-orcas, fishers-dolphins—are now waning. Can we prevent the remaining human-wildlife cooperation from turning into another human–nature conflict? 
 
We recently addressed this question to safeguard the traditional dolphin-fisher cooperative fishing in Brazil. Since the late 1800’s, artisanal net-casting fishers have been interacting with free-ranging Lahille’s bottlenose dolphins to catch migratory mullet in the murky coastal waters of Laguna, southern Brazil. Despite decades of research, we knew very little about how dolphins and fishers coordinate their behavior, the benefits they gain in the short- and long-term, and why these interactions are now declining. These are fundamental pieces to understand how long this cultural practice will persist in face of environmental and behavioral changes, and the cascading effects it will bring. Our interdisciplinary approach combining fine-scale behavioral tracking, long-term demographic surveys and computer simulations uncovered the drivers and consequences of this iconic human-wildlife cooperation and predicted the conditions under which it could go extinct. 
 
We used a multiplatform tracking system to simultaneously record, above and underwater, the interactions between dolphins, fish and humans, and revealed the mechanics of this century-old tradition with unprecedented details. These data show that both dolphins and fishers experience higher foraging success when synchronizing their foraging. Drone-based tracking of dolphins combined with underwater sonar tracking of mullet schools show that dolphins increase the fishers’ foraging success by herding schools toward the edge of the lagoon canal. Field observations coupled with GPS tracking of fishers indicate that fishers standing at this edge wait for a cue by the dolphins—a stereotypical behavior such as a tail slap, head slap or a sudden dive—that indicates the right time and place to cast their nets. This way, dolphins increase prey availability within the reach of the net-casting fishers, who gain higher foraging success—but only when matching the casting behavior with the dolphins’ cues. Acoustic and behavioral tracking of the dolphins’ foraging indicates that, in response, dolphins approach the nets closely underwater during longer dives and engage in very active foraging echolocation as nets sink over the mullet schools—but only when fishers cast their nets according to the dolphins’ cues. Such fine-scale foraging synchrony is, therefore, the key driver of  both predators’ short-term benefits: by working together, both fishers and dolphins benefit by capturing more mullet. In addition, fishers and dolphins that cooperate benefit in the long run as well. 
 
By exploring 12 years of systematic land- and boat-based monitoring of the dolphins’ and fishers’ populations, we found that fishers gain socioeconomic wellbeing and other ecosystem services from interacting with dolphins. More than just food and income, the traditional fisheries with dolphins provide fishers with non-material benefits such as recreation, social connectedness, and cultural belongingness. In parallel, cooperative dolphins experience higher survival rates than their non-cooperative counterparts. Photo-identification and mark-recapture modeling show that cooperative foraging increases dolphin survival by ~13% by minimizing spatial overlap with illegal, bycatch-prone fisheries. However, this long-term data also revealed that dolphin-fisher interactions have been declining recently, threatening both these short- and long-term benefits. This trend mirrors declines in the regional mullet availability while illegal fishing methods that drive dolphin mortality increase. 
 
This rich empirical knowledge allowed us to build numerical models to investigate the fate of the dolphin-fisher fishery under realistic scenarios of declines in mullet availability. These simulations suggest that increasing scarcity of mullets could prompt changes in the use of fishing gear within the local fishing community to target other fishing resources; some gear can increase dolphin bycatch and push the dolphin population toward extinction. While reversing a crash in the mullet stock is very difficult, changing the fishers’ behavior may be more manageable. Our simulations also suggest that conservation actions that incentivize the foraging synchrony with dolphins and remove illegal bycatch-prone fisheries can help to keep the cooperative fishery beneficial for both fishers and dolphins in years to come. Safeguarding cultural practices like this one is an important reminder that aligning human interests with wildlife protection is possible—if both parties work together. 
Original Article:
Cantor, M., Farine, D. R., & Daura-Jorge, F. G. (2023). Foraging synchrony drives resilience in human-dolphin mutualism. Proceedings of the National Academy of Sciences of the United States of America, 120(6). https://doi.org/10.1073/pnas.2207739120

Edited by:

Margaux Héritier , Senior Scientific Editor

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