By: Alexa Kownacki, Ph.D. Student, OSU Department of Fisheries and Wildlife, Geospatial Ecology of Marine Megafauna Lab
Human-wildlife interactions have occurred since people first inhabited the Earth. However, today, when describing human-wildlife interactions specifically in relation to dolphins, frequently we hear about ‘conflicts’. Interactions between fisheries and dolphins that lead to bycatch or depredation (stealing bait/catching from gear) are particularly common. But, symbiotic relationships with dolphin species and certain human groups can also be mutualistic, with both groups benefitting. These symbiotic relationships have been around for hundreds, if not thousands of years.
A depiction of Aboriginal Australians using nets to catch fish in a small inlet with the assistance of coastal dolphins. (Image source: Our Pacific Ocean)
In eastern Australia, cooperative fishing interactions occur
between Aboriginal Australians and dolphins—both bottlenose dolphins and orcas.
In Burleigh Heads National Park, Queensland, AUS, the dolphins are thought to
help the local indigenous Kombemerri (saltwater) people hunt for fish. Indigenous
stories recall men wading into the water with their spears and nets. Then, many
of the men would hit the surface waters to make noises with the splashes.
Underwater, this sound was amplified and then the dolphins would begin chasing
the fish toward the men and their nets (Neil 2002). Aboriginal Australians,
especially those in eastern Australia have an emotional and spiritual
connection to both dolphins and orcas. There are widespread accounts of cooperation
between indigenous people and small cetaceans on the eastern Australian
coastline, which create both context and precedent for the economic and
emotional objectives to contemporary human-dolphin interactions such as dolphin
provisioning (Neil 2002).
Dolphins and fishermen work together in Laguna, Brazil, to catch mullet. (Image Source: Fábio Daura-Jorge)
In the coasts off of Laguna, Brazil, bottlenose dolphins and local fishermen cooperatively fish while tourists gather to watch. Previously, PhD candidate Leila Lemos wrote about these interactions in a blog post. Like many groups of socializing dolphins, these dolphins have a unique whistle to recognize each other. The waters surrounding Laguna, Brazil are murky, turbid and dark green to the point where the fisherman cannot see any of the fish in the water. As the fishermen wade into the murky waters, bottlenose dolphins chase shoals of mullet toward the shore. Then the dolphins tail slap or abruptly dive, “signaling” the fishermen to cast their nets. Research has shown that when the fishermen “work with” the dolphins, both the dolphins and the people catch more, larger fish (Roman 2013). One fisherman claims it is not worth fishing unless the dolphins are around (Roman 2013). Here, the fishermen know the dolphins based on their markings. They know which dolphins participate in the different parts of hunting as well—which dolphin initiates the tail slap, which dolphin usually circles the fish, and which drive the fish towards the coastline. After the dolphins round up and chase the fish for the fishermen and themselves, there is no “reward” from the fishermen for the dolphins—no fish tossed their way. Scientists also found there is a difference in whistle structure between cooperative and non-cooperative dolphin groups (Preston 2017).
A fisherman in Brazil throws a net after dolphins chase mullet into the shore. (Image Source: Leo Francini:Alamy Stock Photo)
Along most coastlines worldwide, humans and dolphins are
competitors. Dolphins are seen as thieves who steal fish out of nets, or get
caught in their gear and ruin fishing opportunities. Thus, dolphins are often unwelcome
near fishing communities. Such negative interactions sometimes lead to
human-caused fatalities of dolphin from gunshots or stabbings, thought to be
from angry fishermen. Yet, in this same
world, fishermen thank the dolphins for bringing their catch to them. Clearly,
both humans and dolphins share high intelligence levels and skills in fishing.
If it is a matter of two minds are better than one, then I think indigenous
communities figured this equation out first: working with the dolphins, and not
against, can better feed their people.
Citations:
Neil, David.
(2002). Cooperative fishing interactions between Aboriginal Australians and
dolphins in eastern Australia. Anthrozoos: A Multidisciplinary Journal of The
Interactions of People & Animals. 15. 10.2752/089279302786992694.
Preston, Elizabeth.
“Dolphins That Work with Humans to Catch Fish Have Unique Accent.” New
Scientist, 2 Oct. 2017,
www.newscientist.com/article/2149139-dolphins-that-work-with-humans-to-catch-fish-have-unique-accent/.
Roman, Joe. “Fishing with
Dolphins: An astonishing cooperative venture in which every species wins but
the fish.” Slate Magazine, 31 Jan. 2013,
slate.com/technology/2013/01/fishing-with-dolphins-symbiosis-between-humans-and-marine-mammals-to-catch-more-fish.html.
(1) Laboratório de Enterobactérias, Oswaldo Cruz Institute/Fiocruz, Rio de Janeiro, Brazil
(2) Grupo de Estudos de Mamíferos Marinhos da Região dos Lagos (GEMM-Lagos)
Background information on Pontoporia blainvillei
The toninha (Pontoporia blainvillei) as it is called in Brazil, or franciscana (Fig.01), is a small dolphin endemic to coastal waters of southeastern and southern Brazil, Uruguay and Argentina. It is the only representative of an ancient lineage of odontocetes, once widely spread over the Pacific and Atlantic oceans. Toninhas occur in waters shallower than 30 m and present a discontinuous distribution from Itaúnas, Brazil (18º 25’S) to Golfo San Matías, Argentina (42º 10’S). The species is considered one of the most threatened small cetaceans in South America due to high, and possibly unsustainable, bycatch levels as well as increasing habitat degradation. Incidental catches in fishing gear, especially gillnets and trammel nets, have been reported along most of the species’ range since at least the 1940s. Other rapidly-increasing conservation issues of significant importance for the franciscana in this region include: (1) habitat degradation, (2) underwater noise, (3) chemical pollution from industrial and urban wastewater, (4) activities related to the exploration and production of oil and gas, and (5) vessel traffic. P. blainvilleiis currently listed as ‘Vulnerable’ in the IUCN Red List of Threatened Species and ‘Critically Endangered’ by the Brazilian Government.
Figure 01: A young Pontoporia blainvillei incidentally caught in gillnets set off the northern coast of the state of Rio de Janeiro, Brazil (December 2011).
In order to guide conservation and management actions on a regional basis, the franciscana range was divided into four zones, known as ‘Franciscana Management Areas’ (FMAs), in the early 2000s. FMA I includes Espírito Santo (ES) and northern Rio de Janeiro (RJ), states located in southeastern Brazil. FMA II corresponds to southern RJ, São Paulo (SP), Paraná (PR) and northern Santa Catarina (SC) states, in southeastern and southern Brazil. FMA III encompasses southern SC and Rio Grande do Sul (RS) states, in southern Brazil, in addition to Uruguay. The last FMA, the FMA IV, corresponds to the Argentina coast (Fig.02).
The absence of stranded or incidentally killed animals indicates a gap of approximately 320 km in the franciscana distribution between northern and southern RJ. This gap separates the southern border of FMA I and the northern border of FMA II.
Figure 02: The FMA areas (in blue) in P. blainvillei distribution range, and the gaps (in white) in toninha distribution along the Northern limit of its distribution in Southeastern Brazil.
The toninha is usually very shy and, for this reason, quite difficult to be seen in the wild. More recently, researchers and citizen science projects have succeeded in obtaining very nice pictures of these animals (Fig.03), which are aiding in elucidating the species mysterious behavior, feeding activity and their preferred habitat conditions.
Figure 03: Toninhas in their natural environment along shallow waters off northern São Paulo state, in the summer of 2019. Photo courtesy of Júlio Cardoso, Baleia à Vista Project.
Figure 04: Aerial view of the Restinga de Jurubatiba National Park and its adjacent waters, the main toninha habitat along the northern coast of Rio de Janeiro. Photo by Salvatore Siciliano (November 2017).
Threats to P. blainvillei along the Brazilian coast
Gillnets are still the main cause of toninha mortality along its entire range. They can be used at the surface or placed at the bottom of the ocean to catch fish, but these nets also entangle this small dolphin (Fig.05, Fig.06).
Figure 05: Gillnets, used at the surface or placed at the bottom of the ocean.
Figure 06: Data on gillnet incidental captures of toninhas (Pontoporia blainvillei) along the northern coast of Rio de Janeiro state collected since1988. Note the concentration of records in the Macaé – Quissamã and Cabo de São Thomé areas, adjacent to the Restinga de Jurubatiba National Park. Data on captures come from Prof. Ana Paula M. Di Beneditto/CBB/LCA/UENF.
Toninhas also face other threats along the Brazilian coast, including environmental chemical contamination by metals and persistent organic pollutants. These pollutants are persistent in the aquatic ecosystem and may accumulate and magnify throughout the tropic chain, causing deleterious effects in the aquatic fauna. Recently, an ecotoxicological assessment from our research group (GEMM-Lagos/Fiocruz) verified, for the first time, significant intracellular concentrations of several toxic metals, such as Hg and Pb (Fig.07), in P. blainvillei individuals sampled along the coast of the Rio de Janeiro state.
Figure 07: Novel HPLC-ICP-MS data on intracellular Pb and Hg in P. blainvillei liver (L), muscle (M) and kidney (K) samples from stranded individuals sampled off the coast of Rio de Janeiro, Brazil.
The monitoring of the contaminant levels in toninhas will potentially aid in conservation efforts, as we can identify which metals are of the most concern, because the intracellular presence of toxic metals indicates high bioavailability, probably leading to deleterious effects.
Conservation Efforts
What is a Whale Heritage Site (WHS) and why we are proposing ‘Mosaic Jurubatiba’ as a WHS?
Situated on the Northern coast of Rio de Janeiro state, Brazil, the Jurubatiba region (Fig.04; Fig.08) is now a Candidate Whale Heritage Site (WHS). The area has been termed ‘Mosaic Jurubatiba’ as the candidate site includes not only the Jurubatiba National Park, but also encompasses other significant sites for conservation along the central-north coast that lie across three municipalities: Macaé, Carapebus and Quissamã (Fig.08).
Figure 08: Proposed extension of the Jurubatiba National Park to the adjacent waters, home of a vigorous population of P. blainvillei. Legend: green – Jurubatiba National Park; red – new terrestrial limit; yellow – new marine limit.
The location provides habitat to a diversity of wildlife. When considering cetaceans, the most regularly seen individuals are the humpback whales, the Guiana dolphins and the toninhas. This is an important site since it is part of the migration route of humpback whales from their breeding and calving grounds, in warm tropical waters, to their feeding grounds, in Antarctica. In addition, this locality is a significant habitat for the toninha, a restricted range species, and the Guiana dolphin, a data deficient species and, therefore, of great concern. The importance of the site becoming a fully accredited WHS is, therefore, evident to further conserve these species and their habitats.
There is a significant amount of active conservation in the Jurubatiba National Park. The Park is the first to exclusively comprise the Restinga ecosystem. Researchers worked alongside authorities and large organizations, such as IBAMA (Brazilian Ministry of Environment and the federal government), to achieve its national park status.
Figure 09: Outreach material produced for the campaign ‘Mosaic Jurubatiba’ to promote education and conservation of the Toninha.
In Quissamã, warning signs were placed along the beaches to alert the population of the importance of the coastal waters as habitat for dolphin species, especially the toninha. This type of cooperation and support of the government and other authorities will aid the candidate site to achieve a full status of WHS.
The long-term goals of the candidate site are to influence the transition away from fishing as a livelihood and to instead embrace the use of responsible tourism to make a living.
For more information on Whale Heritage Sites around the world, visit:
Here you can also find a list of some of the Salvatore Siciliano’s publications on Pontoporia blainvillei:
Siciliano S, de Moura JF, Tavares DC, Kehrig HA, Hauser-Davis RA, Moreira I, Lavandier R, Lemos LS, EMin-Lima R, Quinete N. 2018. Legacy Contamination in Estuarine Dolphin Species From the South American Coast. In book: Marine Mammal Ecotoxicology. Eds. Fossi MC, Panti C. Publisher: Academic Press.
Baptista G, Kehrig HA, Di Beneditto APM, Hauser-Davis RA, Almeida MG, Rezende CE, Siciliano S, de Moura JF and Moreira I. 2016. Mercury, selenium and stable isotopes in four small cetaceans from the Southeastern Brazilian coast: Influence of feeding strategy. Environmental Pollution 218:1298-1307.
Frainer G, Siciliano S, Tavares DC. 2016. Franciscana calls for help: the short and long-term effects of Mariana’s disaster on small cetaceans of South-eastern Brazil. International Whaling Commission SC/66b/SM/04. Bled, Slovenia.
Lavandier R, Arêas J, Quinete N, de Moura JF, Taniguchi S, Montone RC, Siciliano S, Moreira I. 2015. PCB and PBDE levels in a highly threatened dolphin species from the Southeastern Brazilian coast. Environmental Pollution 208.
Lemos LS, de Moura JF, Hauser-Davis RA, de Campos RC, Siciliano S. 2013. Small cetaceans found stranded or accidentally captured in southeastern Brazil: Bioindicators of essential and non-essential trace elements in the environment. Ecotoxicology and Environmental Safety 97:166-175.
de Moura JF, Rodrigues ES, Sholl TGC, Siciliano S. 2009. Franciscana dolphin (Pontoporia blainvillei) on the north-east coast of Rio de Janeiro State, Brazil, recorded during a long-term monitoring programme. Marine Biodiversity Records 2:e66.
