Use of semi-intensive shrimp farms as alternative foraging areas by migratory shorebird populations in tropical areas

Abstract

SummaryEvaluating the ability of anthropogenic habitats to serve as surrogates for natural habitats is an increasingly relevant issue in conservation biology. This issue is especially urgent in tropical coastal wetlands that support large concentrations of migratory shorebird populations and are under pressure from development. Here we evaluated the species composition, abundance, and habitat use of Nearctic migratory shorebirds using recently harvested aquaculture ponds during two non-breeding seasons at shrimp farms surrounding Bahía Santa María (BSM), northwestern Mexico. We also estimated shorebird densities at intertidal units in BSM during and after the harvesting season to explore the connectivity with shrimp farms. Over 25,000 individuals of 25 shorebird species used the surveyed farms (∼13% of shrimp-farm development in BSM; 2014–2015: 10 farms, 994 ha; 2015–2016: 8 farms, 924 ha) during the harvest season. The most abundant species were: Western Sandpiper Calidris mauri, Willet Tringa semipalmata, Marbled Godwit Limosa fedoa, dowitchers Limnodromus spp., Black-necked Stilt Himantopus mexicanus and American Avocet Recurvirostra americana. Numbers of birds decreased as the harvest cycle progressed. Most birds (> 70%) were foraging on the ponds, regardless of tidal stage, while numbers increased during high tide for the most abundant species. At surveyed intertidal areas, shorebird densities were overall similar within and between non-breeding seasons. These results indicate that shrimp farms offer ephemeral but consistent foraging habitats used by non-breeding shorebirds, even in vast coastal wetlands offering a high availability of natural intertidal mudflats. Assuming a similar shorebird use in other shrimp ponds not surveyed within BSM, a significant proportion (> 1% of the biogeographic population) of Willet, Marbled Godwit, and Western Sandpiper, as well as imperilled Red Knot Calidris canutus, might use shrimp farms throughout the harvesting season. Before including current semi-intensive shrimp farms within management plans of BSM, further research is mandatory to assess their utility as alternative foraging habitats for shorebird conservation at tropical areas.