Competition between American mink Mustela vison and otter lutra lutra during winter

The diet of American mink Mustela vison Schreber, 1777 and otter Lutra. lutra (Linnaeus, 1758) and their occupation of the various stretches over approximately 70 km of two Mediterranean rivers in the centre of Spain were studied during January 1995. No spatial segregation is thought to exist between the two species. The otter diet, mainly fish (93% of excrement) and American red crayfish Procambarus clarkii (30%), is no different from that found in other studies. The mink fed mainly on mammals (present in 52% of the excrements) and arthropods (27%), while fish are much less common (19%). The diet is statistically different from that found in a river without otters. The latter eats larger fish and rejects small (< 5 cm) examples, in contrast to mink. The coexistence of the two species is discussed. Despite the considerable overlap in diet the two mustelids can coexist due to the otter's superior ability to capture aquatic prey and the American mink's great degree of ecological adaptability.