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Arraut, Eduardo Moraes; Arraut, J. L.; Marmontel, Miriam; Mantovani, J. E.; Novo, E. M. L. M.
(detail)
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2017 |
Bottlenecks in the migration routes of Amazonian manatees and the threat of hydroelectric dams.
Acta Amazonica 47(1): 7-18. 4 tabs. 7 figs. DOI: 10.1590/1809-4392201600862. Jan./Mar. 2017.
–ABSTRACT: In a particular region within western Amazonia, Amazonian manatees (Trichechus inunguis) live in a floodplain environment that becomes inhospitable for them during the annual low-water season. To flee from it, they undergo a dangerous migration to a refuge while water levels are dropping fast. Our aim was to better understand the role of depth variation in this migratory process. We analyzed the sole tracking data on wild manatees (n=10 males), 30 years of Landsat images, a 14-year hydrograph and a 3-D bathymetric model. Migratory routes contained shallower segments, here called 'migratory bottlenecks', which dried out at the end of most lowering-water seasons, blocking the passage to the refuge. Manatees began migrating just in time to traverse the bottlenecks furthest away, suggesting they fine-tuned their departure so as to maximize time within the foraging home range without compromising safety. They apparently achieved this by estimating depth at the bottlenecks. Moreover, a bottleneck was created in >15 years, illustrating the environment's dynamism and the challenge this imposes upon manatees. Our results are probably generalizable to most of the species' range. We contend manatees possess an updatable cognitive map of their environment and are behaviorally plastic. Current dam-building plans, if implemented, would create more bottlenecks and make flooding less predictable, increasing manatee mortality from unsuccessful migrations. It would also partition the species into small populations, each prone to short-term extinction. The natural outcome would be the second species-level collapse. Economic growth should not come at the expense of the extinction of the iconic manatee.
RESUMO: Em uma região particular da Amazônia ocidental, peixes-boi amazônicos (Trichechus inunguis) vivem em um ambiente que se torna inóspito para eles durante a água-baixa anual. Para fugir dele, realizam uma migração perigosa para o refúgio enquanto o nível da água desce rapidamente. Nosso objetivo foi compreender melhor o papel da variação da profundidade neste processo migratório. Analisamos os únicos dados de rastreamento de peixes-boi selvagens (n=10 machos), 30 anos de imagens Landsat, 14 anos de hidrógrafa e um modelo batimétrico 3-D. As rotas migratórias possuíam trechos mais rasos, denominados gargalos migratórios, que secaram no final da maioria das vazantes, bloqueando o acesso ao refúgio. Os peixes-boi começaram a migração em tempo justo para atravessar os gargalos mais distantes, sugerindo que a sintonizaram para maximizar o período se alimentando sem comprometer a segurança. Para tal, parecem ter estimado a profundidade nos gargalos. Adicionalmente, um gargalo foi criado em <15 anos, ilustrando o dinamismo do ambiente e o desafio que isto impõe aos peixes-boi. Esses resultados provavelmente valem para boa parte da área de distribuição da espécie. Argumentamos que peixes-boi possuem um mapa cognitivo atualizável do ambiente e são comportamentalmente plásticos. Os planos de construção de barragens hidrelétricas, se concretizados, criariam mais gargalos e regimes de inundação menos previsíveis, dificultando a migração e consequentemente aumentando a mortalidade de peixes-boi. Também particionariam a espécie em populações pequenas, vulneráveis à extinção no curto-prazo. O desfecho seria o segundo colapso da espécie. O crescimento econômico não deve vir às custas da extinção do icônico peixe-boi.
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Marsh, Helene D.; Arraut, Eduardo Moraes; Keith Diagne, Lucy; Edwards, Holly H.; Marmontel, Miriam
(detail)
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2017 |
Impact of climate change and loss of habitat on sirenians. Chap. 19 in: Andy Butterworth (ed.), Marine mammal welfare: human induced change in the marine environment and its impacts on marine mammal welfare.
Springer International Publishing: Animal Welfare Series, Vol. 17: 333-357. DOI: https://doi.org/10.1007/978-3-319-46994-2. June 20, 2017.
–ABSTRACT: Although the impacts of climate change on the welfare of individual manatees and dugongs are still uncertain, the effects are likely to be through indirect interactions between meteorological and biotic factors and the human responses to climate change. We divided the potential impacts into (1) those that will potentially affect sirenians directly including temperature increases, sea-level rise, increased intensity of extreme weather events and changes in rainfall patterns and (2) indirect impacts that are likely to cause harm through habitat loss and change and the increase in the likelihood of harmful algal blooms and disease outbreaks. The habitat modification accompanying sea-level rise is likely to decrease the welfare of sirenians including increased mortality. Many species of tropical seagrasses live close to their thermal limits and will have to up-regulate their stress-response systems to tolerate the sublethal temperature increases caused by climate change. The capacity of seagrass species to evoke such responses is uncertain, as are the effects of elevated carbon dioxide on such acclimation responses. The increase in the intensity of extreme weather events associated with climate change is likely to decrease the welfare of sirenians through increased mortality from strandings, as well as habitat loss and change. These effects are likely to increase the exposure of sirenians to disease and their vulnerability to predators, including human hunters. Climate-related hazards will also exacerbate other stressors, especially for people living in poverty. Thus the risks to sirenians from climate change are likely to be greatest for small populations of dugongs and manatees occurring in low-income countries. The African manatee will be particularly vulnerable because of the high levels of human poverty throughout most of its range resulting in competition for resources, including protein from manatee meat.
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Bibliography and Index of the Sirenia and Desmostylia 