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MERCED NWR: Wetlands at Merced National Wildlife Refuge Providing Habitat for...what...Salmon?
California-Nevada Offices , April 28, 2015
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Approximately 2,500 young Chinook salmon were released into Cinnamon Slough, a seasonal wetland at the Merced NWR.  After a month and a half of foraging on a naturally-occuring prey base, many of these fish will be captured and the growth rates will be compared to salmon released at other study sites.
Approximately 2,500 young Chinook salmon were released into Cinnamon Slough, a seasonal wetland at the Merced NWR. After a month and a half of foraging on a naturally-occuring prey base, many of these fish will be captured and the growth rates will be compared to salmon released at other study sites. - Photo Credit: USFWS

By Madeline Yancey

 

The seasonal wetlands of the Merced National Wildlife Refuge (NWR) in Merced County, Calif., are known for supporting tens of thousands of wintering ducks, geese, and sandhill cranes. But a study currently underway seeks to determine whether those same wetlands, like the historic San Joaquin River floodplain wetlands, can provide valuable feeding habitat for young Chinook salmon on their journey to the ocean. Chinook salmon – once a prominent species in the San Joaquin Valley – are to be reintroduced to the San Joaquin River as part of the San Joaquin River Restoration Program.

Joe Merz, a research scientist with Cramer Fish Sciences, partnering with California State University, Fresno, is leading a team that released about 2,500 young salmon into Cinnamon Slough, a seasonal wetland at the Merced NWR. Some of the fish were confined within 30 square-meter net pens while others were released free-swimming into the wetland.

After about a month and a half of foraging in the slow moving water rich with zooplankton like daphnia, copepods, chironomids (midges), and other aquatic invertebrates, the researchers hope to recover at least 100 of the fish.

Measurements will be collected from each fish revealing information about their rate of growth – length, weight, and otolith measurements.

The otolith is a “fish ear bone” – a hard structure composed of calcium carbonate – found in bony fishes. The otolith functions much like the inner ear in mammals, aiding the fish with hearing and balance. When sliced very thin, they reveal growth rings (like the growth rings in a tree trunk) that are formed every day for at least the first six months of a fish’s life.

By measuring the rings of the otolith, fish scientists can determine the growth rate of young fish and quantify the productivity of the habitat in which they’ve been foraging.

Growth rates of the fish in Cinnamon Slough will be compared with those of fish held in a second foraging pen set up in the nearby channel of the Mariposa Bypass on the Merced NWR. The bypass has been identified as a possible channel for future restoration flows of the San Joaquin River.   Historically, according to Merz, flood pulses that fed by winter rainstorms and spring snowmelt would have inundated thousands of acres of valley floodplain. Those same flood pulses carried young salmon downstream where they dispersed into the seasonal wetlands.  Once there, the fish found cover and protection from temperature extremes in the stands of tules and other aquatic vegetation, and an abundance of food.

According to preliminary samples taken one month into the study, Merz said the young salmon in Cinnamon Slough grew from about 42 millimeters to 55 millimeters in length, or about one centimeter per month, an “impressive” growth rate.

One reason Cinnamon Slough was chosen as a study site is because it is connected to the bypass. A secondary study goal is to see whether the flows generated while draining the Slough are sufficient to transport the fish out of the wetland back into the main channel of the bypass, which is where they need to be to continue their journey downstream. Much of the historic San Joaquin Valley floodplain has been disconnected from the main river channel or converted to other uses altogether, so that it no longer functions as a floodplain. Young salmon no longer have access to the bountiful foraging habitat available in the wetlands of the floodplain.

Depending on the data collected in this and additional studies during the next few years, wetlands like those at Merced NWR may contribute to the restoration of suitable rearing habitat for Chinook salmon and to the eventual return of a viable population of salmon once again swimming the waters of the San Joaquin River.

- fws - 

 

Madeline Yancey is a visitor services specialist at the San Luis NWR Complex in Los Banos, California.


Contact Info: Jack Sparks, 209-826-3508, jack_sparks@fws.gov
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