Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
PACIFIC SOUTHWEST REGION: Salmon Egg Survey in the San Joaquin River
California-Nevada Offices , December 17, 2012
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Service biologists wade into the San Joaquin River.
Service biologists wade into the San Joaquin River. - Photo Credit: Cindy Sandoval/USFWS
Biologist Michelle Workman retrieves tube of salmon eggs from a mock redd.
Biologist Michelle Workman retrieves tube of salmon eggs from a mock redd. - Photo Credit: Cindy Sandoval/USFWS
Salmon alevin placed in a tray for sorting.
Salmon alevin placed in a tray for sorting. - Photo Credit: Cindy Sandoval/USFWS

By Cindy Sandoval, External Affairs

On the afternoon of Dec 17, 2012,  fishermen lined up on a bridge near Friant Dam to try and catch a trout or two. A few of the fishermen used store bought jars of salmon eggs as bait, and were unaware that the U.S. Fish and Wildlife Service (Service) was placing their own salmon eggs in the waters below the dam.

These eggs, obtained from the Feather River Fish Hatchery, are part of ongoing studies to reintroduce spring-run Chinook to the San Joaquin River after decades of water diversion have stopped what was once the largest salmon run in the Central Valley. While there are many goals for the San Joaquin River Restoration Project (SJRRP), the Service is the lead agency on fish reintroduction, and is working to promote natural salmon reproduction and self-sustaining populations in the years to come.

During the first week of November, California Department of Fish and Wildlife and Service biologists placed perforated, screened PVC tubes filled with salmon eggs at various points on the San Joaquin River to monitor how salmon eggs will hatch in current river conditions. Each tube was sealed so that eggs and salmon alevin could not be eaten by predators and to ensure an accurate count of the number of eggs hatched. Also connected to the tubes were equipment that monitored water conductivity, dissolved oxygen, and temperature.

Biologists in waders and dry suits walk out into the river to locate and remove the tubes. Removing the tubes is not an easy task as each one is placed in a mock salmon redd to simulate the eggs’ natural habitat and is fastened so the tubes are not washed away. After the tubes are removed from the San Joaquin River and brought to shore, teams open the tubes and separate the contents in trays. Biologists separate unhatched eggs and newly hatched alevin. The alevin –small larval fish– are separated into four groups based on their development and the amount of yolk sac remaining attached to the fish. In natural conditions the yolk sac provides nutrition for the fish for roughly a month until they emerge from the gravel and begin to forage for food.

Data from this survey is compiled so the Service can calculate which areas are likely ready to support salmon spawning and which are not. If a site is found to promote egg survival rates the Service can make small changes to further enhance these sites. “It is important to know what areas are good for egg survival, that way we can focus our efforts where they will do the most good,” said Service Biologist Michelle Workman. One such improvement is adding more gravel to stretches of the river so that alevin can survive their early stages of development and potentially more salmon can reach adulthood and return to the San Joaquin River. The addition of gravel would also allow for more water to flow around the eggs keeping them healthy and decreasing the chances of the eggs being smothered in sand or soil and being destroyed.

One fisherman on the bridge expressed his excitement about the salmon return, “I haven’t had salmon in a while, but maybe the next one I cook will be caught here in the San Joaquin.” The Service will continue to monitor river conditions so when salmon make their return they are able to naturally reproduce and sustain their population.

Contact Info: Cynthia Sandoval, 916-978-6159, cynthia_d_sandoval@fws.gov
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