Pick Our Brain - December 2010
Where do salmon and steelhead go when they leave San Francisco Bay?
The travels of salmon and steelhead in the Pacific Ocean are still something of a mystery but scientists are learning more about this conundrum thanks to new technology and just plain hard work. Here are some findings from past and recent studies.
Figure 1 - Steelhead range in the North Pacific
(Courtesy of Fisheries and Oceans Canada)
Based on historic coded wire tag recoveries, many salmon and steelhead from the West Coast of North America gravitate to a broad swath of the North Pacific stretching from the Aleutians through the Gulf of Alaska (Figure 1), a long way from home. New information, however, indicates that they don’t all make it that far. Tags that record information about geographic location show that some steelhead stick closer to home. Juvenile salmon and steelhead generally make a right turn-head north-when they leave West Coast streams. This fits the idea that they are heading for Alaskan waters but it’s still not known what fraction of the population makes it that far.
This past May the University of California, Davis, Center for Aquatic Biology and Aquaculture held a seminar entitled “Factors Influencing the Salmon Decline in California and the Pacific Northwest”. Bill Peterson, a NOAA Fisheries research biologist presented data on juvenile Chinook and Coho salmon distributions along the Oregon and Washington coasts. These juvenile salmon were collected using large trawl nets. Sampling was at a network of designated sites stretching seaward from the coast to the edge of the continental shelf. Peterson found that juvenile salmon from the Columbia River are mostly found heading north but with an interesting twist. Different species of salmon use different parts of the ocean habitat. Juvenile Coho salmon are found further offshore than juvenile Chinook salmon. Coho seem to prefer the deeper waters over the continental shelf, Peterson noted, while Chinook salmon are most abundant within a couple of miles of shore and have been observed right in the surf zone.
Juvenile salmon from the Sacramento River system also appear to be heading to the north after passing through the Golden Gate. An acoustic tag array off of Point Reyes (the “Point Reyes Line”) has detected a number of salmon and steelhead, presumably on their way to northern Pacific waters.
Some of the most recent and detailed information on salmon and steelhead movement is coming from “archival tags”. These tags record various combinations of location data, depth, temperature, and light conditions. They are attached or implanted in larger fish and later recovered to download the recorded data. Because of the size of archival tags, these can’t be used with juvenile salmon or steelhead. Figure 2 shows the two-month wanderings of a steelhead kelt (adult steelhead after spawning) fitted with an archival tag at Coleman National Fish Hatchery on the Sacramento River and later recovered from this same location. In one four-month period at sea this fish traveled the coastal waters of California from Monterey Bay to Cape Mendocino.
Slowly the great puzzle of where salmon and steelhead spend the ocean phase of their life cycle is beginning to be solved. Understanding the travels of salmon and steelhead in the ocean helps fisheries managers assess how ocean conditions affect their growth and survival.
Figure 2 - Steelhead tracking on the Northern California Coast
(Courtesy of Phil Sandstrom, Biotelemetry Laboratory, UC Davis)