Efficacy of visual encounter surveys for coastal tailed frog detection

Coastal tailed frogs Ascaphus truei inhabit montane streams and forested habitats in the Coast and Cascade Mountains from northern California, USA, to the Skeena River watershed in northwestern British Columbia (BC), Canada. Terrestrial adults and juveniles of this cryptic biphasic species are difficult to survey as they are small, do not vocalize, and may be associated with woody ground structures or subsurface refugia at considerable distances from natal streams. We performed a comparative analysis of the detection rate of post-metamorphic coastal tailed frogs and ecological factors hypothesized to influence detection when conducting visual encounter and pitfall trap surveys. We conducted concurrent surveys in northwestern BC at six sites over similar time periods using both techniques. The average detection rate of visual encounter surveys ( = 0.249, SD = 0.702) was greater than that of pitfall sampling ( = 0.138, SD = 0.773) when cool temperatures and high humidity favor above-ground movement during the daytime. Light-touch ground searches of refuge habitats likely enhanced detection during visual surveys. Although the average detection rate was less, pitfall traps provided 24-hour sampling and were less affected by the experience of the surveyor and the occurrence of ground cover. In general, variation in seasonal behavior influenced detection regardless of method. The relatively higher cost and fixed nature of pitfall traps should be weighed against the ability to apply more cost-effective visual encounter surveys to a greater number of sites.

Genome-wide analysis reveals regional patterns of drift, structure, and gene flow in longfin smelt (Spirinchus thaleichthys) in the northeastern Pacific

The southernmost stock of longfin smelt (Spirinchus thaleichthys) is approaching extirpation in the San Francisco Estuary (SFE); however, patterns of genetic structure, diversity and gene flow which are vital for management are poorly understood in this species. Here, we use genome-wide data to evaluate population structure of longfin smelt across a broad latitudinal scale across estuaries ranging from the SFE to Yakutat Bay and Lake Washington, and fine scale within the Fraser River and the SFE. Results indicate high genetic structure between major estuaries, fine-scale structure within the Fraser River, and low levels of structure within the SFE. Genetic structure was more pronounced between northern estuaries whereas southern estuaries showed shared ancestry and ongoing gene flow, most notably unidirectional northward migration out of the SFE. Furthermore, we detected signatures of local adaptation within the Fraser River and the Skeena River estuaries. Taken together, our results identify broad patterns of genetic diversity in longfin smelt shaped by co-ancestry, unidirectional migration and local adaptation. Results also suggest that the SFE population is genetically distinct from northernmost populations and an important source for maintaining nearby populations.

Flow and Stratification in a Bedrock Confined Estuary

<p>This research describes the impact of the bedrock island structure on the circulation and stratification of a macrotidal, partially mixed estuary in northwestern Canada (the Skeena River Estuary). Due to ongoing development in this formerly remote region, pressures have increased within the Skeena River Estuary over the past decade. However, there is still limited understanding of the estuary's morphodynamics due to its deviation from a 'typical' estuarine morphology. Located along an emergent, fjordal coastline, the Skeena Estuary River drains into a basin confined by bedrock and interrupted by multiple, irregular bedrock islands. Observations suggest that a subaqueous delta, associated facies, and the surface plume are split between several bedrock passages with limited information on the governing hydrodynamic processes. To overcome this, Acoustic Doppler current profiler cross-sectional transects and conductivity, temperature, depth, and turbidity profiles were taken in the nearshore (under 40 m) at locations across the estuary over two different (by ~1000 m<sup>3</sup>s<sup>-1</sup>) river stages. Over multiple dates with various river inflows, the tidal ratio to river inflow produces varied stratification patterns at a given site. During one point in time and river stage, bedrock passages are disproportionally exposed to marine and fluvial inflows, creating spatially diverse stratification patterns across the estuary. Stratification and passage morphology interactions determine the characteristics of tidal slack transitions, with horizontal and vertical separation occurring during well-mixed conditions and stratified conditions, respectively.</p>