RSS FeedsSockeye discovered in the Napa River
Sockeye salmon was added to the list of fish species that can be found in the Napa River last week.
In its second season of monitoring Napa River fish using a rotary screw trap, the Napa County Resource Conservation District (RCD) observed hundreds of unusual looking salmonid juveniles migrating to the Pacific Ocean. The small fish were clearly a type of salmon, but their look was distinctly different from steelhead trout and Chinook salmon, two salmonids that have been known to spawn in the Napa River for decades. Based on conversations with regional biologists, the RCD suspected the unusual salmonids to be chum salmon.
To get a definitive identification of the unknown fish, RCD fisheries biologist Jonathan Koehler sent tissue samples (a small clip of fin) to NOAA for genetic analyses. NOAA extracted DNA from three of the samples, and used genetic marker analyses to determine that the three tested fish are sockeye salmon. NOAA is presently analyzing additional samples to determine if all the unknown fish are sockeye.
Sockeye salmon are the third most abundant Pacific salmon. However, because wild sockeye salmon are typically found in rivers along the Pacific Coast between Oregon and the Canadian Arctic, regional biologists are left wondering: how did sockeye get in the Napa River?
The strongest hypothesis for the observation so far is that the Napa River sockeye juveniles are offspring of the lake dwelling variety of sockeye (called kokanee salmon) that escaped their resident lake. Introduced populations of Kokanee salmon can be found in several lakes in the Sacramento River watershed, such as Lake Berryessa and Lake Shasta. It is possible that Kokanee individuals escaped their resident lake, migrated to the ocean, and then returned to the Napa River to spawn.
Sockeye salmon have a documented history of showing up where they are not expected. A few individuals were observed in the Sacramento River in the late 1940’s, before they were introduced into the Sacramento River watershed lakes in 1952 (Hallock and Fry 1967). The fish found in the 1940’s were also thought to be strays from kokanee populations introduced elsewhere in the state.
Rotary screw trap in the Napa River
