Identifying management actions to increase foraging opportunities for shorebirds at semi-intensive shrimp farms.
Abstract
The expansion of aquaculture has resulted in widespread habitat conversion throughout the world. Identifying beneficial management measures may dramatically reduce negative impacts of aquaculture for migratory birds. We studied how densities of foraging shorebirds varied at ponds within a semi-intensive shrimp aquaculture farm on the north-western coast of Mexico, as related to timing of harvest and tidal cycles. Further, we estimated the total daily available area for each shorebird species throughout two entire harvesting seasons at the shrimp farm. High densities (average ca. 50 individuals per ha) of foraging shorebirds were found during the first days following pond harvest. The most abundant species were Willet Tringa semipalmata and Black-necked Stilt Himantopus mexicanus, followed by Marbled Godwit Limosa fedoa and American Avocet Recurvirostra americana. Other regular, but less abundant, species were whimbrel Numenius phaeopus and dowitchers Limnodromus spp. Densities of shorebirds sharply declined daily following harvest. In addition, the time-window availability of harvested ponds was related to each species' foraging behaviour: <2 days for godwits and dowitchers, 4 days for stilts, 5 days for willets and more than a week for avocets and whimbrels. However, birds continued to use harvested ponds that received a low, but continuous water influx. Our results demonstrate that a tropical shrimp farm represents a patchy environment that provides 4.3-12.7% (depending on species) of its total area as foraging opportunities for shorebirds. Synthesis and applications. Sequential harvesting of shrimp aquaculture farm ponds and increasing moisture of the substrate by providing some water supply to harvested ponds, at least throughout the harvesting period, could integrate shorebird conservation into shrimp-farm production. These low-cost and easy management procedures would not increase costs or affect shrimp production - thus representing a win-win opportunity - and would have potential applications for shorebird conservation throughout the world.