Stream networks expand and contract seasonally; these changes in stream network connectivity affect transfer of matter and energy across trophic levels and between aquatic and terrestrial ecosystems (Ward 1989, Gregory et al. 1991). Although many organisms that live in the headwaters of the stream network are well adapted to seasonal low flows (Frady et al. 2007, Banks et al. 2007), some organisms (e.g., trout) may experience stress from reduced summer habitat and instream food, increased water temperature, and increased vulnerability to predators (Berger and Gresswell 2009). Climate change has the potential to further contract summer stream networks and lead to reduced viability of trout populations in small streams (Wenger et al. 2011, Penaluna et al. 2015). Because long-term research in Mack Creek at the Andrews Forest on two co-occurring aquatic vertebrate species, Mack Creek cutthroat trout, and coastal giant salamander, has revealed complex population dynamics and variable responses to hydrologic variability (Dodds et al. 2012; Arismendi et al. 2020), we are interested in examining whether other stream reaches show these same or different dynamics.
Trout and salamanders are expected to have very different responses to climate change and stream drying because of their habitat requirements and mobility. Areh salamanders able to inhabit and dominate smaller or more disconnected streams than trout? In this project, we are extending our study of these top predators to examine how stream trophic structures differ from headwaters to larger streams across the Lookout Creek stream network. This research will allow us to examine how varying instream and aquatic-terrestrial connectivity influences the ways in which instream predators, fish and salamanders, shape food webs and ecosystem dynamics.
Backpack electroshocking to sample aquatic vertebrates used two methods: mark-recapture and depletion sampling. The sampling was conducted by several groups over time. All sampling involved placing block nets at the upper and lower extent of the study reach, then electroshocking and capture of individuals. Individuals were anesthetized before weighing and measuring of their length and allowed to recover fully before being released in the stream. At multiple transects in each study reach, wetted widths and five or more depths were measured after electroshocking was completed. Data were entered from field data sheets and quality checked using length/weight graphs.
STREAM TEAM sampling was consistently mark-recapture electroshocking with an upstream and downstream pass. This method involved two days of sampling using a single electroshocker and capture with multiple dip netters. On Day 1, all individuals that were captured during shocking, using one pass up then one pass down, were weighed, measured and marked then released. On Day 2, the same area was resampled using same effort for one pass up and one pass down and all individuals captured, measured, weighed and those with marks noted, then released.
PENALUNA_SCALER sampling was electroshocking to depletion with multiple passes upstream and downstream on a single day. Abundances in this database are from the electroshocking at the beginning of the SCALER field experiment in each reach. Two backpack electroshockers, two shocking netters, and a kick seine netter were the sampling team.
WARREN depletion sampling involved 1, 2 or 3 equal-effort passes to sample fish and salamanders from each reach on a single day. Frogs were not sampled.
WARREN mark recapture involved two days of sampling using electroshocking and capture with dip nets. On Day 1 all individuals that were observed during shocking were captured, weighed, measured and marked then released. On Day 2, the same area was resampled and individuals (re)captured, measured, marks noted, and released.
