Summer Distribution and Movements of Juvenile Salmonids in the South Fork Newaukum River, 2016

Habitat, temperature, and fish distribution patterns of the Chehalis River tributaries were identified as data gaps by the Aquatic Species Enhancement Plan Technical Committee of the Chehalis Basin Strategy (Aquatic Species Enhancement Plan Technical Committee, 2014). This information is needed to address questions pertaining to the development of flood reduction strategies, including a proposed dam, and to anticipate fish responses to the combined effects of future restoration actions and climate change, both of which may further influence fish habitat through changes in the physical, hydrological, and thermal environment. The South Fork Newaukum River, a tributary in the Chehalis River watershed, was selected for study due to the regional interest in pursuing habitat restoration projects in this river basin.

The primary objectives of this study were to 1) describe the landscape and habitat characteristics of five delineated reaches, 2) describe spatial and temporal summer stream temperature patterns, 3) describe spatial and temporal summer fish species distributions, and 4) describe the direction and timing of juvenile salmonid movements. With these data, we explored how juvenile salmon and steelhead distributions and movements were associated with physical habitat and landscape characteristics, stream temperature, and native cyprinid fish distributions throughout the summer rearing period.

The study area was a continuous 37.5 km section of the main stem South Fork Newaukum from elevation 264.9 m (river km 56.6) downstream to the confluence with the North Fork Newaukum River at elevation 81.6m (river km 19.1). We collected continuous temperature data at 12 locations throughout the survey area and collected spatially continuous habitat and fish data throughout the survey area. Fish data were collected by four snorkel surveys that occurred between May and September 2016. The study area was partitioned into five study reaches that represented variability in landscape characteristics of the basin. Five passive integrated transponder (PIT) detection arrays framed each reach to collect broad scale movement patterns of juvenile salmonids across the survey area. We captured and PIT tagged juvenile Chinook salmon (Oncorhynchus tshawytscha), coho salmon (Oncorhynchus kisutch) and steelhead (Oncorhynchus mykiss) from locations within each study reach that were 2.2 - 4.0 km from the nearest PIT detection array.

The study area was characterized by an upstream-downstream pattern of valley confinement, gradient, and land cover. Upstream reaches were characterized by relatively confined valley walls, higher gradient, and land cover dominated by forest compared to downstream reaches which were characterized by less valley confinement, lower gradient, and cultivated land cover. Habitat characteristics among reaches were minimally variable compared to landscape and temperature features however we detected some variability in large woody debris and pool frequency among the five reaches.

We documented an upstream-downstream pattern in temperature that changed over time. Upstream locations were consistently cold and downstream locations were consistently warm with the month of August having the warmest temperatures. Central locations of the study area had a greater daily range of temperature relative to extreme upstream and downstream extents.

We documented an upstream-downstream pattern in summer fish distribution that changed over time. Juvenile salmonids consistently dominated upstream locations (colder) whereas cyprinids consistently dominated downstream locations (warmer). In the downstream-most reach, juvenile salmonids occurred in low densities throughout the study period. In the adjacent reach (second-most downstream), juvenile salmonid densities decreased sharply from July to August concurrent with increasing temperatures and increases in densities of cyprinid species and hatchery-origin juvenile steelhead in this reach. We conclude that the combination of warm temperatures and competing or predatory native fish species may contribute to declining densities of wild juvenile salmon and steelhead in the downstream reaches of the South Fork Newaukum over the summer months.

We observed extensive summer movements of juvenile coho and steelhead, and the directionality of movements changed over time. In total, 24.1% and 18.3% of the PIT tagged coho and steelhead, respectively, were detected at least once, demonstrating movements at least ~2-4 km during the study period. In the summer months (July, August), coho and steelhead had a higher proportion of upstream movements in downstream than upstream reaches. This movement pattern likely contributed to the observed upstream shifts in fish distribution during summer months. However, disproportional mortality among reaches is also possible and may confound this interpretation. In the early fall (September), the majority of movements for coho, and to a lesser extent steelhead, were downstream.

We observed several anthropogenic influences that may conflict with restoration goals to increase productivity of wild fish populations. For example, construction of man-made obstructions (e.g., ‘rock dams') were encountered throughout the survey area. Rock dams may inhibit fish movements, especially during summer base flows. In addition, residualized hatchery steelhead had substantial overlap with wild juvenile salmonids, and this overlap is higher in reaches with the highest potential for future restoration actions. In the reach with greatest spatial overlap, residualized hatchery steelhead were approximately to one in every three juvenile steelhead encountered.

Based on results of our study, we offer the following recommendations for restoration planning for juvenile salmon and steelhead summer rearing habitat in the South Fork Newaukum River:

• The upstream most reaches (R3.4, R4.5, and R5) may be good candidate areas for protection of existing riparian and stream conditions,
• The downstream most reaches (R1.2 and R2.3) may be good candidates for habitat enhancement focused on reducing summer stream temperatures. A watershed analysis currently in process will diagnose potential to improve stream temperatures through habitat enhancement in these reaches,
• Restoration would benefit from a combination of education and enforcement actions that minimize construction of man-made obstructions (e.g., ‘rock dams') which inhibit fish movements during summer base flows, and
• Managers should review current hatchery practices in the Newaukum River in order to develop strategies to reduce the residualization of hatchery steelhead.