Biology and habitat use of three-spined stickleback (Gasterosteus aculeatus) in intermittent Mediterranean streams.
The three-spined stickleback has one of the largest distribution ranges among freshwater fishes, being found in marine, brackish and freshwater environments in Eurasia and North America. Throughout its huge range, stickleback is often abundant and thus it is considered a non-threatened species. However, stickleback populations have steeply declined towards the species’ southern bounds, especially in Mediterranean areas. In the Iberian Peninsula the species is now considered as endangered, after experiencing multiple local extinction events.
In spite of this, until now there was an almost complete lack of information on the biology of Mediterranean sticklebacks. In this work we report the first available information on the biology and habitat use of stickleback in Mediterranean streams.
We first focused on growth, condition and reproduction of stickleback, using data from over 6000 measured fish that were captured along almost 100 fishing events throughout the year. We found that populations were strictly annual, with most adults dying immediately after their first reproduction and no evidence of survival up to the second reproduction season. Adult post reproduction mortality coincided with a period of extremely low somatic condition. Juveniles growth showed an almost complete stop during summer, when somatic condition was also low, but experienced a high and continuous growth during autumn, winter and early spring. This growth pattern differed from that of sticklebacks elsewhere, which usually stops in winter, and from that of other native species in Mediterranean streams, which does not show the summer growth stop.
We then analyzed stickleback habitat use using fyke nets during spring and summer in 118 sites. Stickleback populations were detected in 50 sites, occupying mainly intermediate locations along fluvial gradients. The presence of abundant aquatic vegetation was the main factor related with both stickleback presence and the abundance of its populations. This could be related the fact that male sticklebacks build nests, mainly from vegetation material, where they guard eggs from one or several females. Stickleback abundance was also negatively related with that of invasive fish and crayfish species. Stickleback tended to occur in native-dominated fish communities, being almost absent from lower stream reaches, which bear high abundances of invasive fish species.