| Summary: | Tese de doutoramento, Biologia (Ecologia), Universidade de Lisboa, Faculdade de Ciências, 2012 The Eurasian otter (Lutra lutra), a protected predator, competes with man for water, in drier regions, and for fish in important fish rearing areas. This thesis addresses man-otter conflicts, by examining: i) otter distribution and persistence in a waterscape facing natural water shortage, yet aggravated by human activities; and ii) otter damages in fish rearing areas, to further understand the level of conflict and of reconciliation needed. The IUCN Otter Specialist Group recommends a standardized 10x10 km UTM grid for monitoring otter distribution and trends. As a result of the national survey, otters were downgraded to a “Least Concern” category in the 2005 Portuguese Red Data Book. However, by interpreting a continuous distribution at the coarse 10x10 km resolution, serious threats to local otter populations, like climate change and increased water scarcity, may be overlooked. To assess the effect of survey resolution, otter distribution in the Sado river basin was evaluated at three scale resolutions (10x10, 5x5, and 2.5x2.5 km). Results confirmed that even though otters were widely distributed, the 10x10 grid cell protocol is too optimistic and misleading when local management decisions are involved and conservation planning is needed. A monitoring protocol is suggested to improve conservation management in Mediterranean areas of intermittent water flow. Many Portuguese fish farms are located in estuarine protected areas. The degree of conflict between otter conservation and fish farming was assessed at Sado river estuary by using otter visiting rates to fish farms and the otter consumption of commercial fish. Otter damage was assessed by combining the percentage of consumption of reared species with otter daily food consumption, daily visitation rates and number of otters visiting each fish farm. Landscape descriptors were analyzed to identify key landscape factors for damage. Results indicate high visiting ...
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