Habitat Use and Movement of Sea-Run Cutthroat Trout in the Salmon River Estuary

Lisa Krentz - M.S. Candidate, Dept. of Fisheries and Wildlife, Oregon State University

Sea-run cutthroat trout (Oncorhynchus clarki clarki) populations in Oregon have undergone a significant decline in the past decade. Causes of decline likely include large scale habitat degradation of freshwater and estuarine environments.

Sea-run cutthroat trout migrate extensively throughout their life, exploiting a complex array of habitats between headwater streams, estuary, and nearshore ocean. However, their habitat requirements are poorly understood. Although sea-run cutthroat trout are thought to be highly dependent upon estuarine habitats, the number of studies that address this topic are relatively few and it is not possible to make generalizations about movement patterns. This lack of knowledge makes it difficult to design and implement management and restoration activities that will sustain both the population and the fishery. My project proposes to: 1. Obtain a life history description of sea-run cutthroat trout 2. to identify critical habitat, including the sequence and timing of estuarine habitats being used 3. to estimate the amount of time spent at sea and 4. to determine the role that the estuarine environment plays in the life history of the species. It is my hope that this study will provide a basis for preservation of critical habitats and will help us to better understand how to restore and preserve sea-run cutthroat trout in other coastal rivers.

These objectives will be met by combining both acoustic and passive integrated transponder (PIT) technology:

Cutthroat trout were PIT tagged during their downstream migration. Extensive seining was conducted in the estuary to recapture tagged individuals and determine habitat use. PIT tagging of individual fish has allowed us to obtain growth data over time. In the first year of the study, 2002, we were wildly successful in recapturing individuals, with a recapture rate of approximately 20%. The second year of the study proved to be similarly successful and we were able to track newly tagged individuals as well as those tagged in the previous year.

We also used acoustic tags to track 43 adult fish in the estuary. Acoustic receiver stations were set up at different locations within the estuary and encompassed a wide range of habitat types. The receivers recorded the fish ID number as each individual came within range. This information enabled us to determine when cutthroat are entering the estuary, how long they are staying and in what habitat types, when they are moving off-shore, and when they are returning from the sea. This information provides us with habitat use as well as variability of movement patterns within the population. Preliminary analysis has identified at least two life history types: an estuarine resident form that does not migrate to the ocean but, rather, resides in the estuary for many months and exhibits strong site fidelity while doing so; and an ocean migrant form that completes the migration to sea and, upon return, may potentially spend a number of months in the estuary before migrating upstream.

In addition, the physical characteristics have been mapped. Salinity, temperature and depth were measured throughout the estuary. This will enable us to examine whether associations between these physical parameters and habitat use by cutthroat can be made.

The study takes place in the Salmon River just north of Lincoln City on the Oregon coast and will be integrated into a larger study of the Salmon River watershed and estuary, where studies are currently underway to examine how restoration of salt marshes and wetlands may aid in the recovery of chinook, coho, and chum salmon, and steelhead trout. It is hoped that this study as a whole will point the way for recovering federally listed salmonids in other watersheds and fulfill a goal of the Oregon Plan for Salmon and Watershed to restore Oregon's salmonids to sustainable levels.