DOI: 10.7291/d1fx0z
title: Sea otters in a California estuary: Detecting temporal and spatial dynamics with volunteer monitoring

description: Volunteer monitoring can support conservation of imperiled wildlife, by
 providing higher resolution data in space and time than those available
 from professional scientists. However, concerns have been raised that data
 collected by amateurs are inaccurate or inconsistent and thus do not allow
 for robust detection of spatial or temporal trends. We evaluated the rigor
 and value of volunteer monitoring data for one iconic wildlife species,
 the southern sea otter (Enhydra lutris nereis), in Elkhorn Slough estuary
 in central California, USA, and explored whether volunteer monitoring
 could provide added value to complement limited professional surveys.
 First, we compiled and analyzed sea otter counts taken on daily ecotourist
 boat trips along the estuary, and then compared temporal patterns to data
 collected by professional scientists tasked with monitoring this federally
 listed species. Second, we analyzed data on sea otter abundance, habitat
 use, and behavior collected by a team of trained volunteers, the Elkhorn
 Slough Reserve Otter Monitoring Program. Overall, we demonstrated the
 ability to detect important ecological patterns relevant to sea otter
 conservation and wetland habitat management using volunteer-derived
 datasets. Long-term trends and inter-annual variability were similar
 between professional agency monitoring data and volunteer datasets.
 Moreover, the much higher frequency of volunteer observations allowed for
 seasonal and tidal dynamics to be detected that could not be revealed by
 less frequent professional monitoring. We found higher sea otter abundance
 in the estuary in spring–summer, indicating seasonality in use of the
 estuary. We detected differences in habitat use of the estuary between
 higher and lower tides, and greater frequency of foraging at low tide and
 in certain areas. Volunteer observations revealed fine-scale differences
 in habitat use: eelgrass beds were used much more heavily than adjacent
 areas only a few meters away. Volunteer data can thus provide critical
 information about coastal habitat use and behavior that can improve
 conservation strategies for threatened wildlife species.
description: Four CSV files with data from basic field surveys of southern sea
 otters in Elkhorn Slough estuary, central California, USA are provided. 
 The data almost entirely consist of otter counts conducted by visual
 surveys; one file also contains data on the percentage of otters observed
 foraging.  A complete description of the study objectives, methods, field
 sites, and uses of these data for analyses and interpretations can be
 found in the associated paper, Eby et al. 2022. The
 Otter_Elkhorn_LongTerm dataset consists of data from three sources, 1)
 ecotourist counts from the Elkhorn Slough Safari boat, 2) volunteer
 observations from the Elkhorn Slough Reserve Otter Monitoring Program, and
 3) annual range-wide surveys coordinated by USGS.  For the latter, we used
 only otter counts from the lower Elkhorn Slough estuary. USGS southern sea
 otter data are made available annually, e.g. for 2019 here: https://doi.org/10.3133/ds1118.  These publically available data emphasize the value of 3-year running averages for larger regions, while the dataset archived here has annual counts just for the local Elkhorn Slough estuary. The other three datasets represent data collected by volunteers for the Reserve Otter Monitoring Program. 
description: These are CSV files; no special programs or software
 required.