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.

Movement and habitat use of non‐breeding Semipalmated Sandpiper (Calidris pusilla) at the Banco dos Cajuais in Northeast Brazil

“…In many areas of South America, changes to shorebird habitats in coastal areas are a direct result of human activities, and in northeast Brazil the main impacts are related to the conversion of mangroves and associated habitats into salinas and shrimp farms (Ferreira & Lacerda, 2016; Valenti et al, 2021). Although some previous studies have suggested that shrimp farms can be important to shorebirds and other waders (Basso et al, 2018; Masero, 2003; Navedo & Fernández, 2019), such heavily altered habitats, including both shrimp farms and salinas , may also present a greater overall risk via general habitat reduction, exposure to predators such as feral cats, environmental degradation and exposure to contaminants like heavy metals during non‐breeding periods (Burger et al, 2019).…”

“…Recent estimates suggest that 20,000–30,000 ha of coastal habitat was being used for shrimp production in 2020 (Lacerda et al, 2021). While shrimp farms have provided alternative foraging habitats for shorebirds in some cases (Basso et al, 2018; Navedo et al, 2015; Navedo & Fernández, 2019), the actual importance and potential impacts of these highly modified habitats for shorebirds in other locations is relatively unknown (Burger et al, 2019).…”

Effects of aquaculture on the maintenance of waterbird populations

“…In the face of large-scale loss of natural habitat (Newbold et al, 2015;Diaz et al, 2019), expanding artificial landscapes, such as farmlands, commercial saltpans, and plantations, sometimes provide alternative habitat for wildlife (Ma et al, 2010;Katayama et al, 2019). Understanding the role of artificial habitats in wildlife population maintenance has become essential for biodiversity conservation (Navedo & Fernández, 2019;Wang et al, 2022). The global aquaculture industry has expanded rapidly.…”

Semi‐intensive shrimp farms as experimental arenas for the study of predation risk from falcons to shorebirds

“…In northwestern Mexico, semi‐intensive shrimp farms (following Edwards, 1993 ) enmeshed within surrounding coastal wetlands are widely used by shorebirds to forage throughout the shrimp‐harvesting period between October and December (Navedo & Fernández, 2019 ; Navedo et al., 2015 ). These anthropogenic habitats represent ideal arenas to study trade‐offs between starvation and predation risk from a complete ecological perspective for a number of reasons.…”

“…These anthropogenic habitats represent ideal arenas to study trade‐offs between starvation and predation risk from a complete ecological perspective for a number of reasons. First, high densities of Nearctic shorebirds forage at recently harvested ponds, even at those shrimp farms adjacent to or embedded with large coastal wetlands (Navedo & Fernández, 2019 ). Second, predators as peregrine falcons ( Falco peregrinus ) are often observed hunting on shorebirds at shrimp farms (Basso et al., 2018 ).…”