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

Abstract

Recent studies show that the availability of prey in¯uences the ecology of otters by regulating breeding, carrying capacity and mortality. Mediterranean habitats experience extreme seasonal variation in water ow ± a stress period can occur in summer when water¯ows and levels are low with long periods of drought, while torrential¯oods usually occur in autumn and spring. Reservoirs can affect this situation by further in¯uencing water¯ow regimes and acting as a barrier. Our data show the close relationship between the amount of food (®sh) available to otters and their use of a stretch of water and the otter density there. The adjustment of the number of individuals (and carrying capacity) in an area can be seen from their mortality, a decrease in their reproductive success, or migration. Our results are consistent with the hypothesis that otters are food-limited. Torrential rains, summer droughts and dams for water management have repercussions for otter 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 conservation and management of the otter in these habitats must not ignore the management 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 cessation of¯oodwater from reservoirs must be progressive and mimic more closely the¯ow regime of natural rivers.

Non-perennial Mediterranean rivers in Europe: Status, pressures, and challenges for research and management

“…These have shown that desiccation influences the availability of prey such as fish, which again may strongly affect the European otter (Lutra lutra) (Clavero et al, 2003;Ruiz-Olmo and Jiménez, 2009). Consequently, the mortality rate of otters increases, their abundance diminishes, and breeding success declines (e.g., Ruiz-Olmo et al, 2001). Furthermore, due to summer droughts, the breeding time of otters occurs earlier in Mediterranean than in temperate streams (Ruiz-Olmo et al, 2002).…”

Eurasian otter (Lutra lutra) prey selection in response to a variation of fish abundance

“…Accordingly, the otter may be considered a generalist aquatic predator, even though only a few studies have simultaneously compared otter diet to food availability (Lanszki & Körmendi 1996;Carss et al 1998;Lanszki et al 2001;Ruiz-Olmo et al 2001).…”

New records and update on the geographic distribution of Lontra longicaudis (Olfers, 1818) (Carnivora: Mustelidae) in Seasonally Dry Tropical Forests of northeastern Brazil

“…In this region, otters can frequently occur in almost dry rivers, provided that some ponds exist; this is not directly related to the availability of water itself, but to the availability of prey, which include mostly aquatic species (Ruiz-Olmo et al 2001;Ruiz-Olmo et al 2007).…”

“…The reduction in the amount of water during these periods also increases the risks associated with foraging, as the otters need to look for food more frequently in shallow areas or out of water, where semi-aquatic species are weaker competitors than terrestrial species, and become more vulnerable to predation and to becoming roadkill (Ruiz-Olmo et al 2001;Ruiz-Olmo & Jiménez 2008b). The reliance on ponds also makes them more vulnerable to being harassed and killed by local fishermen (Carrillo-Rubio & Lafón 2004).…”