The influence of fish abundance on the otter (Lutra lutra) populations in Iberian Mediterranean habitats

Recent studies show that the availability of prey influences the ecology of otters by regulating breeding, carrying capacity and mortality. Mediterran ean habitats experience extreme seasonal variation in water flow - a stress period can occur in summer when water Rows and levels are low with long pe riods of drought, while torrential floods usually occur in autumn and sprin g. Reservoirs can affect this situation by further influencing water flow r egimes and acting as a barrier. Our data show the close relationship betwee n the amount of food (fish) available to otters and their use of a stretch of water and the otter density there. The adjustment of the number of indiv iduals land carrying capacity) in an area can be seen from their mortality, a decrease in their reproductive success, or migration. Our results are co nsistent with the hypothesis that otters are food-limited. Torrential rains , summer droughts and dams for water management have repercussions for otte r populations in as much as they affect their prey-species. Barbels Barbus spp. and, secondarily, nases Chondrostoma spp. are shown to be important to otter ecology and breeding in Mediterranean Iberian rivers. The conservati on and management of the otter in these habitats must not ignore the manage ment of food sources. In order not to affect otter populations, the effect of the reservoirs and their dams also must be considered. The release and c essation of floodwater from reservoirs must be progressive and mimic more c losely the flow regime of natural rivers.