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Ecotourism is a strategy for biodiversity conservation, but it involves possible negative effects on animal health and welfare. Large predators such as crocodilians are one of the great public attractions sought after for tourist interactions. Interactions with wild animals and humans can hyperstimulate the hypothalamic‐pituitary‐adrenal axis in the short term, in the case of crocodilians showing an increased corticosterone level, which is indicative of physiological stress. Between September and December 2019, we simulated interactions between tourists and Amazonian crocodilians at Anavilhanas National Park in Central Amazonia, Brazil to evaluate the effects of handling and use of photographic flashes on black caiman (Melanosuchus niger) and spectacled caiman (Caiman crocodilus) on circulating corticosterone and lactate. Corticosterone levels increased 1.7‐fold during handling and 2.7‐fold when exposed to photographic flashes in black caiman but not in spectacled caiman. Increased corticosterone concentrations in black caiman were characterized by an increase caused by handling and were more intense after flashes than in controls, but the combination of handling and flash had no effect. During handling in simulated tourist interactions, anaerobic respiration increased lactate in black caiman but not in spectacled caiman. The effect of simulated tourist interactions with Amazonian crocodilians was dependent on the handling and especially on flash use in black caiman. The results can assist management, conservation programs, and public policies, especially in programs based on tourism interaction with Amazonian crocodilians. [ABSTRACT FROM AUTHOR]

When captured, free‐living crocodilians respond by hyperstimulation of the hypothalamic‐pituitary‐adrenal (HPA) axis, which triggers a cascade of downstream events of physiological stress. We examined these responses in two unstressed, and stressed Amazonian caimans, Caiman crocodilus and Melanosuchus niger. Plasma corticosterone levels increased in both stressed caiman species. In M. niger, the levels of this hormone increased 5.2‐fold compared with the basal range values, while in C. crocodilus this was only 1.7‐fold. After stress, M. niger needed more than 6 h to return its corticosterone levels to basal range values, whereas in C. crocodilus just 0.5 h was enough. Downstream events were characterized by an increase in glucose levels, which is associated with corticosterone increments. Excessive muscle activity resulted in increased plasma lactate content in both species. Lactate levels were also related to plasma calcium concentration, possibly due to the buffering capacity for preventing lactic acidosis. Clearance of excessive lactate load was faster in M. niger (0.5 h) than in C. crocodilus (more than 6 h). Although both caiman species respond in the same way to capture, the amplitude and duration of activation of the HPA axis are different. M. niger may be potentially more sensitive to acute stress than C. crocodilus. On the other hand, C. crocodilus needs more time to recover from the lactic acid load. Our experiment provides a useful diagnostic tool for management and conservation programs, as well as evaluating the impacts of tourism and recreational capture on caimans in the Amazon. Highlights: In both stressed species, capture stress resulted in increased plasma corticosterone, glucose, lactate, and calcium levels.The physiological responses observed in Melanosuchus niger indicate that it is more susceptible to acute stress conditions. [ABSTRACT FROM AUTHOR]