Eric D. Chapman

Diel movements of out-migrating Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss) smolts in the Sacramento/San Joaquin watershed

We used ultrasonic telemetry to describe the movement patterns of late-fall run Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (O. mykiss) smolts during their entire emigration down California’s Sacramento River, through the San Francisco Bay Estuary and into the Pacific Ocean. Yearling hatchery smolts were tagged via intracoelomic surgical implantation with coded ultrasonic tags. They were then released at four upriver locations in the Sacramento River during the winters of 2007 through 2010. Late-fall run Chinook salmon smolts exhibited a nocturnal pattern of migration after release in the upper river. This is likely because individuals remain within a confined area during the day, while they become active at night and migrate downstream. The ratio between night and day detections of Chinook salmon smolts decreased with distance traveled downriver. There was a significant preference for nocturnal migration in every reach of the river except the Estuary. In contrast, steelhead smolts, which reside upriver longer following release, exhibited a less pronounced diel pattern during their entire migration. In the middle river, Delta, and Estuary, steelhead exhibited a significant preference for daytime travel. In the ocean Chinook salmon preferred to travel at night, yet steelhead were detected on the monitors equally during the night and day. These data show that closely related Oncorhynchus species, with the same ontogenetic pattern of out-migrating as yearlings, vary in migration tactic.

Behavior, movements, and habitat use of adult green sturgeon, Acipenser medirostris, in the upper Sacramento River

We conducted the first continuous shipboard tracking of southern Distinct Population Segment green sturgeon, Acipenser medirostris, in the Sacramento River. Tracking of adult green sturgeon occurred between river kilometer (rkm) 434.8 and 511.6, a section of the putative spawning grounds located near Red Bluff, California. The recorded positions of acoustically tagged green sturgeon were analyzed using First Passage Time analysis to determine differences in habitat use between suitable and non-suitable habitats. Classification and Regression Tree modeling was used to determine explanatory inputs attributable to above average habitat use. Green sturgeon exhibited above average habitat use at five sites, identified as potential spawning aggregate sites. Three types of movements (holding, milling, and directed) could be categorized from tracks. Lastly, we show that green sturgeon while on the spawning grounds exhibit a high degree of mobility throughout the spawning grounds, often making large movements between specific habitat units. Our study illustrates how the application of shipboard tracking can be useful for describing movement, behavior and habitat utilization at a spatial scale not achieved by stationary acoustic monitors.

Movements of steelhead (Oncorhynchus mykiss) smolts migrating through the San Francisco Bay Estuary

We used acoustic telemetry to monitor the out-migration of 1,000 steelhead smolts (Oncorhynchus mykiss) through the San Francisco Bay Estuary during spring of 2009 and 2010. The smolts transited the estuary rapidly (2–4 days) and utilized flows in the main channel during their migration. Fewer smolts were detected in marinas, tributaries and other shallow areas surrounding the estuary. Many of the smolts made repeated upriver and downriver movements that were related to the tidal flow, moving upstream during flood tides and downstream during ebb tides. These results show that steelhead smolts migrating from the Sacramento River transit rapidly through the lower reaches and do not use the estuary for feeding, rearing, or smoltification purposes.