Summer survival and habitat characteristics of a threespine stickleback (Gasterosteus aculeatus L.) southern European population.

Abstract

In April 2006, the relationships between the spatial distribution of a threespine stickleback (Gasterosteus aculeatus L.) southern European population during breeding season and the environmental parameters were investigated in the Almansor River, a Mediterranean type river in Portugal. This species distribution and survival rate during the previous summer period were also taken into account in this study. Despite the high mortality suffered by the juvenile in the upstream summer pools, the threespine stickleback adults continue to prefer this river stretch for spawning. In this period, male sticklebacks showed preference for sites that were rich in _sh species and vegetation, where there is a greater protection against environmental fluctuations and anthropogenic pressures. Male distribution was also dependent on predation risk, for they were more abundant at sites with fewer potential predators. The abundance of females was positively related to male abundance, showing that, above all other variables, male nesting site was the main factor influencing their distribution, during breeding season.