fish report header

Counting Bass

There are common questions that anglers and fish biologists often ask, such as What kinds of fish are found in this river? and How many are there? It's often assumed that we have answered such basic questions long ago, but it's not as easy as it sounds. Many factors can affect the abundance of fish species, including environmental factors like flow, temperature, and contaminants, or ecosystem factors like food supply and predator abundance. Recently, there has been growing interest in how many adult striped bass (Morone saxatilis) migrate into the San Joaquin River during their spring spawning migration.  


Since 1969, the California Department of Fish and Wildlife  (DFW, formerly "Fish and Game") has been conducting a mark-and- recapture study to monitor the population dynamics of Central Valley striped bass, focusing on the Sacramento River and the Delta (see DFW reports). The estimated population of legal-sized striped bass remained relatively stable early in the study, but then declined in the late 1970s and 80s (Kohlhorst 1999). In response, DFW began a hatchery stocking program, but discontinued it in 1991 due to concerns about predation on endangered salmonids (Harris and Kohlhorst 1996). DFW studies found a subtle shift in the 1960s and 70s in spawner abundance, with fewer fish spawning the San Joaquin River and Delta and more in the Sacramento River, presumably due to poor water quality (e.g., higher salinity) in the San Joaquin (Turner 1976). With so many recent changes in water quality, water flows, and fish species composition in the estuary, people are curious about the current abundance of striped bass in the San Joaquin River basin.


DFW targets striped bass for their population study during the spring spawning migration in the Sacramento River, and uses large fyke traps north of the city of Sacramento. These traps have two internal fykes that funnel fish into the nose of the trap. We at FISHBIO have been curious whether fyke traps could be used for a similar project to estimate the population of striped bass specifically in the San Joaquin River, and decided to assess the feasibility by conducting a pilot study. After visiting traps operated by DFW and the Department of Water Resources, a few weeks of hard work in the Fab Lab (see What the fyke?), and a survey of potential trap sites, we launched two fyke traps into the river in early May.


We fish the traps for 24-hour periods and check them each morning. Several species may be captured on a given day, providing a glimpse into the species composition of the river. To date, we've caught American shad, largemouth bass, white catfish, suckers -- and many striped bass. We measure all the striped bass, examine them for existing tags or marks, and tag the legal-size fish with a yellow disk tag, following the same methods DFW has used for decades. We also insert a PIT tag into each striped bass. In the future, we could monitor individual striped bass moving into the river's tributaries using PIT tag antennas attached to weirs throughout the basin. There is a reward for anyone who recaptures these disk-tagged striped bass and provides us with the relevant information. If you fish the San Joaquin River or South Delta, you may want to keep an eye out for our yellow tags. It could be your lucky day!

Follow Us! Like us on Facebook Follow us on Twitter View our photos on flickr View our videos on YouTube
email list
Recent Blog Post

FISHBIO in the classroom 

Summer is almost here, but FISHBIO staff recently found ourselves heading back to school. We gave a presentation about our work to four groups of sixth graders at an elementary school in Oakdale as part of their annual Agricultural Day. In keeping with the Ag Day theme, we drew the connection between people and fish through our shared need for water. More than 90% of the average Californian's water footprint goes toward producing the food we consume (see What's your water footprint?). While water is undeniably important for agriculture, it also means everything to fish. We talked about the importance of sharing this precious natural resource, and helped the class visualize their place in the watershed along the Stanislaus River, a tributary of the San Joaquin River. We also traced the amazing journey that young salmon make from Oakdale to the ocean -- a trek of 165 miles!

Most students were well versed in the salmon life cycle, and the majority had seen salmon spawning upriver at Knight's Ferry as part of their fourth grade curriculum. One student even pointed out that our photo of a steelhead was a great example of countershading, an adaptation that helps fishes hide from predators and prey. The fishes' dark backs make them hard to spot when looking down on them from above, while their silvery bellies make them blend into the sunlight when looking up from below. It's nice to know at least a few facts get...  Read more> 

IN THE NEWS: Recent stories you might have missed...
Statewide survey maps sport fish contamination in California rivers
Lake County News 

Concentrations of contaminants such as methylmercury and pesticides in sport fish were found to be low at the majority of locations sampled in the first-ever systematic statewide survey of California rivers and streams. The fish survey, conducted by the State Water Resources Control Board's Surface Water Ambient Monitoring Program (SWAMP), surveyed sport fish from 63 locations in 2011. The survey analyzed sport fish because they provide information on potential human exposure to contaminants, and on the condition of the aquatic food web... Read more> 

Delta takes its place among top 10

Stockton Record

California's Delta has been rated in the top 10 of the best black bass fishing lakes in the United States by Bassmaster Magazine, putting a spotlight squarely on a truly amazing fishery that sits right at Stockton's doorstep.

James Hall, editor of the magazine based in Birmingham, Ala., said the final list of lakes was based on data from state wildlife scientists and catch rates of countless fisheries, coupled with recommendations from bass... Read more > 

Chinook salmon study breaks ground in bay, Delta
San Mateo County Times

On a sunny morning in the state capital, Mike McHenry, a fisherman out of Pillar Point Harbor in San Mateo County, guided his boat to a dock on the Sacramento River and readied its 10,000-gallon hold for some special cargo.
Once the captain had filled the tank with river water, a team of state Fish and Wildlife biologists and technicians aimed a 100-foot tube into the belly of McHenry's 64-foot boat, the Merva W. About 100,000 baby salmon gushed out... Read more > 

Climate change study: 82% of California native fish species risk extinction
Sacramento Bee
Climate change may cause the extinction of 82 percent of California's native fish species, including iconic ones such as Central Valley salmon and Delta smelt, according to a new study. The peer-reviewed study by fishery experts at UC Davis created a framework to measure how vulnerable numerous species are to climate change. It assesses habitat conditions, climate change projections and temperature sensitivity for the 121 native and 50 nonnative fish species that inhabit California... Read more > 
Another "banner year" for wild spring-run Chinook salmon
Chico Enterprise Record

People who know fish are expecting another "banner year" for threatened spring-run chinook salmon in Butte Creek. All but a few stragglers have made their way from the ocean, through the delta, along the Sacramento River, up Sutter Bypass and Butte Slough to Butte Creek Canyon. The fish rest in pools for the summer, living off fat stored in their bodies. In September, they will spawn and die. From creekside cliffs, the fish look like dark shadows... Read more >