Fish in the littoral zone: ecology, threats and management

AbstractThe importance of the littoral zone of lakes to a diversity of fish species has been appreciated for many centuries, although the complexity and heterogeneity of this habitat have resulted in a poorer understanding of local fish ecology compared with that achieved for typically much larger but simpler offshore habitats. Lake fish species may occupy the littoral zone permanently or visit it on diel, seasonal or ontogenetic timescales in response to a range of intrinsic and extrinsic factors. The purposes of such occupations include feeding, refuge from predation and, most importantly for many species, reproduction. The primary environmental threats to fish in the littoral zone arise from eutrophication, which may directly or indirectly alter feeding conditions through the loss of macrophytes, from increases or decreases in water level variations and from siltation rates, both of which may interfere with spawning or egg incubation, and from the introduction of alien species, many of which preferentially colonise the littoral zone where they may act as predators, competitors or environmental degraders. The management of these threats is best accomplished through general lake management measures such as the control of nutrient levels, but some actions specific to the littoral zone or its fish populations are also feasible. These include the replacement of lost or damaged spawning substrata, the active management of water levels at appropriate times of year, and, at least potentially, the deployment of artificial structures to provide appropriate physical habitat for adult fish