Conservation of Mediterranean otters: the influence of map scale resolution
2012
Sales-Luís, Teresa | Bissonette, John A. | Santos-Reis, Margarida
Recent work in landscape ecology has stressed the importance of scale considerations in studies of biological diversity and conservation. The IUCN Otter Specialist Group has recommended a standardized 10 × 10 km UTM grid for monitoring Eurasian otters (Lutra lutra) distribution and trends. As a result of subsequent surveys, otters were downgraded to a “Least Concern” category in the 2005 Portuguese Red Data Book, primarily because of its broad distribution at the 10 × 10 km scale. Previously, otters were considered threatened and used by conservationists as a flagship species in river conservation. However, by interpreting a continuous distribution at the coarse 10 × 10 km resolution, the new status assessment can be misleading and, as a result, managers may ignore serious threats to local otter populations. To assess the effect of survey resolution, we evaluated otter distribution in the Sado river basin (Alentejo, Portugal) during both wet and dry seasons at three scale resolutions (10 × 10, 5 × 5, and 2.5 × 2.5 km). Stream length, as well as reservoir edge and area were measured at each grid cell size and compared for grid cells with and without otter presence. Our results confirmed that even though otters were distributed widely, the 10 × 10 grid cell protocol overestimated the area actually occupied. Seasonal effects were also very significant. The 10 × 10 km grid resolution may be useful when trying to assess European or national population trends but is too optimistic and misleading when local management decisions are involved and conservation planning is needed. We suggest a monitoring protocol to improve conservation management in Mediterranean areas of intermittent water flow.
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