Physiological Characteristics of Migrating Steelhead Trout Kelts from the Snake River System

Steelhead trout (Oncorhynchus mykiss) are iteroparous, but the degree of repeat spawning varies throughout their range.  In the Snake River, the proportion repeat spawning is often less than 2%. In a collaborative multi-year study, we are examining several non-lethal methods to determine factors that may be affecting the survival of post spawning steelhead (kelts) in the Snake River system, with a goal of increasing the rate of iteroparity in the population. To better understand the relationship of physiology, fish condition and migration success, we sampled blood from downstream migrating kelts at Lower Granite Dam, WA, assessed their external condition, and applied a PIT-tag in the pelvic girdle. We collected blood samples from 308 kelts in 2009 and 851 kelts in 2010 at the juvenile bypass facility at Lower Granite Dam, WA.  Blood plasma was placed into one of four factors; nutritional, electrolyte, tissue damage, or hormone. We used multivariate and univariate statistical analyses to examine a suite of physiological metrics, and their association with fish external condition (rated as good, fair, and poor), gender, hatchery (adipose clipped), adipose intact (with or without dorsal fin erosion), and migration timing.  We compared selected “smolt” metrics from downstream migrating kelts, such as sodium/potassium ATPase and T4 hormones with those typical for migrating juvenile smolts and found few correlations. Fish condition affected many of the biochemical plasma parameters. Nutritional and electrolyte factors were significantly higher in good condition fish.  Tissue damage factors and stress hormone were higher in poor condition kelts than those in good condition.  We found few differences by gender and A-run (<70 cm ) and B-run (>70 cm) kelts. Among kelts with adipose fins, we compared good condition fish with and without dorsal fin erosion and found fish with no dorsal erosion had higher nutritional factors and fish with dorsal fin erosion had higher tissue damage factors. We found several differences by monthly comparisons of April, May, and June. April was highest for electrolytes. Nutritional factors did not vary. The kelts sampled in 2009 had several nutritional factors (cholesterol, triglycerides, and calcium) that were significantly higher than kelts sampled at the same time in 2010. Electrolytes (sodium, potassium, and magnesium) were also higher in 2009 than in 2010. Tissue damage factors (LDH and AST) as well as stress hormone cortisol were also higher in 2009 than in 2010.