Relative leaping abilities of native versus invasive cyprinids as criteria for selective barrier design

Restoration of river connectivity favors the spread of native but also of exotic invasive populations, mainly freshwater fish. This has rarely been studied, and never between migrating cyprinids. To harmonize both objectives, the feasibility of a selective leaping barrier for migratory cyprinids is studied through the measurement of fish leaping capabilities while freely migrating at a weir in the Guadiana River of southwest Spain. A cross-population analysis provided the cost-benefit outcomes of completely blocking the invasive Carassius auratus while allowing negotiation for most of the native Luciobarbus sp. populations. Larger fish reached higher leap heights, the highest being attained by the native barbel species. Barbels reached up to four times its total length and a maximum height of approximately 150 cm, while the figures for the invasive goldfish were double total length with a maximum of approximately 80 cm. The selective obstacle height (SOH) for goldfish was 81.2 cm, the estimated maximum height that the tip of a jumping goldfish could reach. Facility designs (whether culvert, weir or fish pass) with this SOH criterion guarantees complete migration failure of goldfish. Also, most (95-99%) of the barbels migrating populations will surpass the SOH regardless of body length; only the less capable or those in poor condition will be blocked. Advice on SOH utility to evaluate existing instream structuresand their position within the cost-benefit balance-is provided.