Abstract
Recent droughts raise global concern over potential biodiversity loss and mitigating impacts to vulnerable species has become a management priority. However, drought impacts on populations are difficult to predict, in part, because habitat refuges can buffer organisms from harsh environmental conditions. In a global change context, more extreme droughts may turn previously suitable habitats into ecological traps, where vulnerable species can no longer persist. Here, we explore the impacts of California's recent record‐breaking drought on endangered juvenile Coho salmon. We estimated the variability of cumulative salmon survival using mark–recapture of nearly 20,000 tagged fish in intermittent stream pools during a 7‐year period encompassing drought and non‐drought conditions. We then determined the relative importance of physical habitat, streamflow, precipitation, landscape, and biological characteristics that may limit survival during drought. Our most striking result was an increase in the number of pools with reduced or zero survival during drought years and a coincident increase in spatial variability in survival among study reaches. In nearly half of the stream pools, salmon survival during drought was similar to mean survival of pools assessed during non‐drought years, indicating some pools had remarkable resistance (ability to withstand disturbance) to extreme drought. Lower survival was most attributable to longer duration of disconnection between upstream and downstream habitats, a consequence of increasing drought severity. Our results not only suggest that many pools sustain juvenile salmon in non‐drought years transition into ecological traps during drought but also highlight that some pools serve as refuges even under extreme drought conditions. Projected increases in drought severity that lead to longer droughts and greater habitat fragmentation could transform an increasing proportion of suitable habitats into ecological traps. Predicting future impacts of drought on Coho salmon and other sensitive species will require identification and protection of drought refuges and management strategies that prevent further habitat fragmentation.
Highlights
Droughts are an increasing threat to ecosystems worldwide, with unprecedented multi-year droughts recently observed in California, Australia, and South Africa (Robeson, 2015; van Dijk et al, 2013; Vogel & van Zyl, 2016)
We addressed the question of how extreme drought influences species survival in intermittent streams and identified the primary environmental factors controlling the occurrence of refuges and ecological traps
Droughts are predicted to increase in frequency and severity but there remains high uncertainty about potential impacts to species given the uncertain persistence of habitat refuges (Morelli et al, 2017; Thuiller et al, 2004)
Summary
Droughts are an increasing threat to ecosystems worldwide, with unprecedented multi-year droughts recently observed in California, Australia, and South Africa (Robeson, 2015; van Dijk et al, 2013; Vogel & van Zyl, 2016). Coho salmon (Oncorhynchus kisutch) in the Shasta River of northern California successfully spawn in river reaches that become inhospitable during the juvenile rearing period as a consequence of increased human water withdrawals These reaches have been transformed from suitable dry-season rearing habitat into ecological traps for this highly endangered fish population (Jeffres & Moyle, 2012). Salmon trapped in drying streams can experience reduced survival, likely due to declines in dissolved oxygen as well as increased water temperatures, competition, and/or predation (Grantham, Newburn, Mccarthy, & Merenlender, 2012; Hwan, Fernández-Chacón, Buoro, & Carlson, 2018; Obedzinski, Nossaman, Horton, & Deitch, 2018; Woelfle-Erskine, Larsen, & Carlson, 2017) Both broad-scale climatic factors, such as drought severity and local-scale anthropogenic activities, appear to control the balance between intermittent stream habitat serving as drought refuges or acting as ecological traps for salmon (Jeffres & Moyle, 2012; Magoulick & Kobza, 2003). We predicted that streamflow and habitat fragmentation would be the most influential variables in explaining variation in salmon survival
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
