Abundance, demography, and harvesting of water snakes from agricultural landscapes in West Java, Indonesia

Abstract

Context Across much of its geographic range, the masked water snake, Homalopsis buccata, is harvested each year in large numbers, questioning the sustainability of that offtake. Aims To quantify abundance and demography of water snakes in anthropogenically disturbed habitats in an area of West Java, where these snakes are subject to intensive harvest. Methods We accompanied professional snake-collectors, and conducted our own surveys of ponds and irrigation canals, to record the numbers and attributes (species, sex, size, etc.) of snakes that were captured using a variety of methods. Key results Snakes of several species were abundant, with mean capture rates of 32 666 snakes km−1 of irrigation canals, and 57 501 snakes km−2 of fishponds (9500 and 43 788 for H. buccata alone). Sex ratios of H. buccata were female-biased in ponds but not irrigation channels. Ponds underlain by deeper mud contained more snakes. Collecting methods varied among habitat types, in a way that reduced collateral risk to commercially farmed fish in ponds. Conclusions These water snakes are extremely abundant in Java, despite high levels of historical and continuing harvest. The inference of low population sizes for H. buccata in Indonesia, as presented in the IUCN Red List, is erroneous. Implications An ability to utilise anthropogenic resource subsidies (in this case, fish farmed in village ponds) allows some native predator species to attain remarkably high abundances, and to withstand intense efforts at harvesting.