DOI: 10.5061/dryad.pzgmsbcqv
title: Spraints demonstrate small population size and reliance on fishponds for Eurasian otter (Lutra lutra) in Hong Kong

description: Lack of data on population sizes and resource requirements are major
 impediments to the effective conservation of rare species globally. The
 conservation of the Eurasian otter (Lutra lutra) in Hong Kong reflects
 many of these key challenges for elusive and difficult-to-study mammals.
 It is a rare carnivore that has narrowly escaped extirpation, now
 surviving within a human-dominated environment. Using sign surveys and
 spraint analysis, we recorded only 40 fresh spraints from 246 otter signs
 locations, over four months of intensive sampling across two years.
 Records were restricted to the Mai Po wetlands, confirming this as the
 core area for Hong Kong’s otter population. Molecular analysis and
 microsatellite genotyping identified a minimum of seven individuals, two
 pairs of which were likely related. The genetic and sign data together
 strongly indicate a small population. Fish dominated the otter diet,
 highlighting the importance of fishpond habitats as a premium foraging
 resource. Given the rapid changes surrounding the Mai Po area (especially
 the new Northern Metropolis Development Strategy), maintaining quality and
 connected habitats, in addition to sustaining commercial fishponds will be
 key to otter recovery and long-term population viability in Hong Kong.
description: Surveys for otter spraints were undertaken during the winter
 (dry) season of 2018 and 2019 in Hong Kong, avoiding higher temperatures
 and humidity (affecting DNA quality of samples), and overgrown vegetation
 (affecting sample detectability). Surveyors experienced in otter survey
 traversed the banks of all accessible fishponds, gei wai, freshwater, and
 tidal watercourses across the study area (located in the north-west New
 Territories of Hong Kong, along the east coast of Inner Deep Bay in the
 Pearl River Delta). The survey was repeated at least two times each season
 to increase the probability of detection and thus decrease the probability
 of false negatives (MacKenzie et al., 2006). During the surveys, spraints
 between 1 and 3 days old were collected and frozen while being transported
 to the lab (Taastrøm and Jacobsen, 1999). Spraints were soaked in a
 diluted solution of alkaline detergent at room temperature prior to being
 rinsed and air-dried (24-48 hr) and then sieved through a 1 mm mesh.
 Identifiable hard prey-remains were separated, examined using a dissecting
 microscope, and weighed. For the otter diet study, six
 main food categories were considered: fish, amphibians, birds, mammals,
 crustaceans, and other invertebrates, based on the following undigested
 remains: bones, scales, feathers, fur, exoskeleton, antennae, articulate
 extremities, and insect wings. Fish species were identified to the lowest
 taxonomic level using a personal reference collection developed, existing
 databases, and taxonomic keys (Conroy et al., 2005; Groves and Cornwall
 Mammal Group, 2020; University of Nottingham, n.d.). Where present,
 amphibians, and reptiles were typically identified from their
 characteristic bones; bird prey from feathers and beak and leg/claw
 remains; mammal remains from teeth and hair; undigested integuments for
 insects, and shells for crustaceans. No attempt was made to identify
 non-fish categories below class level. A minimum of
 eleven taxa were recovered from the spraint samples. Fish represented the
 major component of the otter diet, while birds, other invertebrates, and
 crustaceans represented a very small proportion of the diet.
 To investigate relatedness between otter individuals, faecal DNA
 was extracted and amplified with seven microsatellite markers from an
 initial set of fourteen markers (Dallas and Piertney, 1998; Huang et al.,
 2005). All samples were genotyped following the multiple-tubes approach to
 ensure reliable genotyping (Taberlet et al., 1996).
description: This folder contains two csv files, with
 “Otter_Spraints_Prey_Items.csv” containing data regarding otter diet, and
 “Otter_microsat_data.csv” containing microsatellite data regarding otter
 relatedness.