In the FOURTH national otter survey in Spain, 8,024 sampling points were carried out
covering the entire Spanish mainland. The only province where no sampling was Almeria.
The UTM grid (10x10 km) was used as a sampling unit, with a total of 4,019 grids
prospected, representing 77.3% of the grids of mainland Spain. Of all sampling, 4,822
(60.1%) 600 meters and 3,202 (39.9%) were spot-check.
An ... [Show full abstract] overall value of 5,199 locations sampled with a positive presence of otter was obtained,
representing 64.8%. Regarding UTM grids (10x10 km), 2,920 were positive, with the
presence of otter, as at least one point was found with valid otter traces or signals, with
76.4% of the grids sampled. Positive grids with the presence of otter accounted for
59.9%, which was the percentage of the territory of mainland Spain with otter.
Overall, the results were more positive in the western half than in the eastern half, and
more positive in the northern half than in the southern half. By autonomous communities,
the maximum percentage of positive locations and positive grids was reached in Galicia,
with 95.4% and 96.8% respectively. On the opposite bank, the minimum values of
positive localities and grids were obtained in the Valencian Community (15.0% and
Of the 41 peninsular provinces, the presence of otter was detected in all of them, except
in one, Almería, which was not sampled. This sampling included Andorra within the
autonomous community of Catalonia, increasing the locations, grids and sampling area
compared to previous surveys. The provinces with the poorest presence of otter were
Alicante (1.5%), Gipuzkoa (13.3%), Murcia (15.4%) and Bizkaia (22.2%), counted as a
percentage of grids with the presence of otter with respect to the total (Murcia) and with
respect to the sampled grids (Alicante, Biscay and Gipúzkoa).
Otter was found present in all watersheds in mainland Spain. The distribution of otter was
significantly higher in the Basins of the Atlantic and Cantabrian slope, where 69.7% of the
positive seasons (n= 5,169 surveyed) were reached, and lower on the Mediterranean side:
55.9% positive (n= 2,855 surveyed). The highest altitudes, above 2,000 m, where otter
was found was in Lleida and Andorra (Pyrenees) and Palencia (Cantabrian Mountains).
With regard to the Third Survey, otter has continued to expand, more slowly, and mainly
in Mediterranean areas. The numbers and percentages indicate a similar distribution of
otter than that occupied in the 2000s, but we believe that it is because in some territories
a significant number of grids with the presence of otter in the third poll not were sampled
in this survey.