(Adam Weybright’s Thesis Research)
Movement patterns in juvenile salmonids can be highly variable among individuals and across stream networks. Varying degrees of movement among juvenile coho salmon have been attributed to competition, physical habitat, streamflow characteristics, and genotypic variation. The influence of these factors differs with the life history stage of the fish, but will ultimately affect the way coho salmon utilize nursery habitat and may influence their size as smolts. The relationship between juvenile coho salmon size and movement patterns has been documented but the results are ambiguous. The goal of this study is to identify juvenile coho salmon movement strategies among habitats and to examine possible relationships between those strategies and their effects on fish growth rates and final body size (as indicators of apparent fitness). Five objectives are part of the proposed research: 1) to determine whether the spring and summer movement strategies of juvenile coho salmon in lowland coastal streams in southern Oregon are limited to sedentary and nomadic or if there are more patterns that emerge when movement is examined at different temporal and spatial scales; 2) to identify the proportion of each movement strategy type among juvenile coho populations; 3) to examine whether juvenile coho salmon movement strategy types are correlated with habitat quality; 4) to examine whether seasonal growth rates and late summer body size of juvenile coho are correlated with habitat quality; and 5) evaluate whether seasonal growth rates and late summer body size of juvenile coho are related to unique movement strategies exhibited by juvenile coho.
(Katherine Nordholm’s Thesis Research)
We are using Passive Integrated Transponder (PIT) tags to monitor movement of coho in two coastal lowland streams. Fish are tagged as juveniles and their movements are recorded at a variety of in-stream antenna arrays. After rearing for a year in the ocean, adult coho return to the rivers to spawn. PIT tagged fish detected during this return migration are being used to calculate marine survivals for lifecycle monitoring projects in the systems. These returning adults are comprised of fish that showed both nomad and sedentary rearing strategies as juveniles. Spawning ground surveys are conducted to recover carcasses and biological samples are collected. These samples include scales, tissue, and otoliths.
Otoliths are bones in a fish’s head that grow continuously throughout a fish’s life. As the bone is formed it captures the chemical signal of the water surrounding the fish. Since otoliths collected from PIT tagged carcasses come from fish with known juvenile life history patterns, we will compare otoliths chemical analysis with known estuary entry times to determine if this method can reliably detect early estuary rearing patterns in coho.