OPTIMIZING HABITAT SUITABILITY FOR SALMONIDS IN THE EEL RIVER: A STUDY OF TEMPERATURE AND DISSOLVED OXYGEN DYNAMICS

The purpose of this research is to investigate temperature and dissolved oxygen differences at varying locations and depths to identify thermal refugia that support the survival of endangered juvenile salmon and steelhead in the drier season within the Eel River and its tributaries in the Angelo Coast Range Reserve in Northern California. Temperature and DO are important to juvenile salmon as they don’t survive well in high temperature and low DO waters. They need DO levels of 5mg/L or higher, and ideal temperatures range from 17 to 20°C. Temperatures between 20 to 24°C are survivable, but may result in adverse effects in growth, development, and lifespan. Temperatures above 24°C are considered unsuitable. Data were collected in August during the low-flow period. DO and temperature were measured within river channels and pools accessed by hiking, kayaking, and swimming in the South Fork of the Eel River. The data gathered includes readings from data loggers for continuous monitoring of DO and temperature in the Wilderness Lodge Pool and manual temperature and DO measurements in this pool and the shallower inflow and outflow creeks.

A statistically significant inverse correlation between depth and DO and depth and temperature in the Wilderness Lodge Pool of the Eel River indicates thermal stratification that could impact juvenile salmon survival. Shallow depths were generally warmer and therefore less suitable throughout the day. Mornings were found to be most suitable due to lower temperatures throughout the pool, while suitability diminished in the afternoon with increasing temperatures. DO was found to be too low at greater depths generally more than 13ft. This results in more unsuitable conditions for salmonids in the shallowest and deepest depths of the pool. The data loggers showed that moderate depths around 9ft remained the most suitable throughout a 48 hour period, with temperature and DO remaining within ideal ranges. This research provides data relevant to the survival of juvenile salmon in the drier season and how climate change could impact the watershed. If temperatures continue to rise, salmonid habitat could continue to diminish, and finding areas of thermal refugia will be increasingly important.