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The southern distribution of the Broad-snouted Caiman (Caiman latirostris Daudin 1802) in Argentina occurs in Santa Fe Province, where its population has been under management by "Proyecto Yacaré" since 1990. From 1997 to 2016, we captured 77 nesting female Broad-snouted Caimans in Santa Fe Province. Our results suggest that previously defined size classes for Broad-snouted Caiman do not adequately describe the reproductively mature female segment of the population. Here we propose to change size ranges for general size classes for Broad-snouted Caiman. In addition, we have observed that reintroduced reproductive females by Proyecto Yacaré represent about 32% of captured females. These results indicate that reintroduced females by the management program are surviving and reproducing in the wild at least up to 20 years.Keywords: management, size class, reproduction, sexual maturity. Tamanho de fêmeas nidificantes do jacaré-de-papo-amarelo (Caiman latirostris Daudin 1802)Resumo Na Argentina, a distribuição mais austral do jacaré-de-papo-amarelo (Caiman latirostris Daudin 1802) ocorre na Provincia de Santa Fe, sendo que suas populações são manejadas pelo "Proyecto Yacaré" desde 1990. Entre os anos de 1997 e 2016, nós capturamos 77 fêmeas nidificantes do jacaré-de-papo-amarelo em Santa Fe. Nossos resultados sugerem que as classes de tamanho definidas para o jacaré-de-papo-amarelo não representam a realidade dos animais capturados no presente estudo. Portanto, propõe-se uma alteração nas classes de tamanho para o jacaré-de-papo-amarelo. Nós também observamos que as fêmeas reintroduzidas pelo "Proyecto Yacaré" representaram 32% das fêmeas capturadas. Estes resultados indicam que fêmeas reintroduzidas pelo programa de manejo estão sobrevivendo e reproduzindo na natureza por, pelo menos, 20 anos.Palavras-chave: manejo, classe de tamanho, reprodução, maturidade sexual.

Considerando a importância da técnica histológica na sexagem de quelônios e os poucos trabalhos direcionados para esta técnica, é proposto neste estudo caracterizar morfometricamente e histologicamente as gônadas de P. expansa e P. unifilis. Todos os espécimes utilizados neste trabalho foram procedentes do rio Javaés, entorno do Parque Nacional do Araguaia, Estado do Tocantins, Brasil. Após estudo sob estereomicroscópio, foram coletadas as gônadas para o procedimento histológico de rotina. Foram analisadas 187 amostras de P. expansa, das quais 81,2% foram identificadas como fêmeas e 18,7% como machos; e 98 de P. unifilis, das quais 31,6% eram fêmeas e 68,4% machos. Não foram verificadas diferenças microscópicas relevantes na sexagem entre estas espécies. Os critérios utilizados no diagnóstico microscópico foram principalmente a morfologia das gônadas, a presença do apêndice no oviduto remanescente, a morfologia do oviduto e as características das células de revestimento dos folículos e túbulos seminíferos. Quando comparadas as medidas biométricas dos ovários e testículos, somente foram observadas diferenças para a largura.

Evaluation of factors associated with predation on Caiman latirostris nests (Crocodylia: Alligatoridae) in Argentina. Predation is a major cause of crocodilian egg loss. However, at present, the mechanisms by which predators detect nests is unknown. Previous studies have reported that predators are able to detect prey using both visual and olfactory cues. This study aims to determine the natural predation rate on Broad-snouted Caiman (Caiman latirostris whether olfactory or visual cues attract predators to caiman nests, and to evaluate the effect of maternal presence on nest predation. In December 2010, we searched for nests in the north of Santa Fe Province, Argentina. Each nest was assigned to one of the following treatments: (1) control nests (nests were observed from a distance to avoid disturbance), (3) olfactory attraction nests (nests were opened, one egg from the clutch was broken, and then the nests were covered again), (4) olfactory attraction from human disturbance (material was manipulated by researchers). The natural predation rate on broad-snouted caiman nests was found to be 21% during the nesting season. Both olfactory and visual cues were associated with increased predation rates, and human disturbance was strongly associated with increased nest predation at terrestrial sites. Predation rates were less at nests attended by female caiman. Management programs that harvest eggs in wild populations (ranching) are predicated on the assumption that removal of some eggs is the remaining hatchlings will have improved survival rates. To reduce nest predation of Broad-snouted Caiman between the time when the nest is found and when the eggs are they are found.Keywords: attraction, Broad-snouted Caiman, eggs, human disturbance, nesting, signs/ tracks, olfactory sensory cues, visual sensory cues. ResumenEvaluación de los factores asociados con la predación de nidos de Caiman latirostris (Crocodylia: Alligatoridae) en Argentina. de huevos de cocodrilianos. Estudios previos reportan que los predadores detectan a las presas mediante signos visuales u olfativos, por ejemplo los producidos por el hombre. Los objetivos de Caiman latirostris),olfativas o visuales atraen a los predadores a los nidos y si la presencia materna afectaría la predación de los nidos. Para este trabajo, buscamos nidos en el norte de la provincia de Santa Fe (Argentina) durante diciembre de 2010 y los asignamos a los siguientes tratamientos: "control" (nidos observados a la distancia para evitar disturbios), "atracción visual" (cintas amarillas atadas a la vegetación alrededor de los nidos), "atracción olfativa" (los nidos fueron abiertos, uno de los huevos fue roto, y se cubrieron nuevamente los nidos) y "atracción olfativa por disturbios humanos" (el material del nido fue manipulado por los investigadores). Encontramos que, durante una temporada reproductiva 21%. Observamos que rastros olfativos y visuales incrementan la tasa de predación, y los disturbios humanos estuvieron asociados al incremento de la tasa de predación de nidos...

The Tocantins-Araguaia Basin is one of the largest river systems in South America, located entirely within Brazilian territory. In the last decades, capital-concentrating activities such as agribusiness, mining, and hydropower promoted extensive changes in land cover, hydrology, and environmental conditions. These changes are jeopardizing the basin's biodiversity and ecosystem services. Threats are escalating as poor environmental policies continue to be formulated, such as environmentally unsustainable hydropower plants, large-scale agriculture for commodity production, and aquaculture with non-native fish. If the current model persists, it will deepen the environmental crisis in the basin, compromising broad conservation goals and social development in the long term. Better policies will require thought and planning to minimize growing threats and ensure the basin's sustainability for future generations.

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Podocnemis expansa e P. unifilis são animais de vida longa, com uma demorada maturação sexual, o que influencia uma baixa taxa de substituição de indivíduos. Suas populações são caracterizadas por uma pequena mortalidade dos animais adultos, mas alta taxa de mortalidade de filhotes e embriões. Sendo a predação natural de ninhos e filhotes um dos fatores mais importantes do baixo sucesso de eclosão dessas espécies. No rio Javaés, os ovos e recém-eclodidos podem ser predados por uma grande diversidade de animais: dentre as aves, urubus (Coragyps atratus e Cathartes aura), carcará (Polyborus plancus), jaburu (Jabiru mycteria); lagartos (Tupinambis teguixin) e mamíferos de pequeno porte, coati (Nasua nasua) e cachorro-do-mato (Cerdocyon thous). Do total anual de desovas de P. unifilis em média 65,98% são predadas, sendo 41,68% de forma total e 24,30% parcialmente. Enquanto que apenas 5,31% das ninhadas de P. expansa são sempre parcialmente predadas. Dentre os predadores aquáticos existem diversos peixes, principalmente piranhas (Serrasalmus nattereri) e jacarés (Melanosuchus niger e Caimam crocodilus). Os predadores das fêmeas de P. unifilis são: jacaré-açu (Melanosuchus niger), onça-pintada (Panthera onca) e onça-parda (Puma concolor). Enquanto que as fêmeas de P. expansa em postura, somente são predadas por P. onca. As fêmeas de P. unifilis em postura são predadas num total médio de 3,93% anualmente, enquanto que para P. expansa a média anual é 5,66% das fêmeas.

Crocodilian-human conflicts, caused especially by urban expansion and habitat destruction, have been considered one of the main threats to the conservation of these species worldwide. In Brazil, such conflicts have been documented with crocodilian species all over the country. This study identified 400 conflict events in on-line journalistic news between humans and caimans within Brazilian cities between 2016 and 2021. Caiman latirostris (57.3%) was the most common species found in large urban centers in the Northeastern and Southeastern regions. Most encounters in which the date was informed were registered in the wet season (64.5%), and the rescues were mainly carried out by the environmental military police and fire brigades. We outlined management protocols to be undertaken by environmental agencies during crocodilian rescues to minimize animal stress and risk of accidents. The increasingly common interaction between humans and caimans in urban environments is an important alert to envisage best conducts for the coexistence between people and caimans in Brazil and shows the need to invest in public policies to mitigate the negative effects of urbanization on wildlife.