Chinese Mitten Crab As a Potential Host for Lung Flukes

p. 12-13. Walter and Culver discuss the potential for the recently established Chinese mitten crab to serve as an intermediate host to human parasitic lung flukes. It is presently unknown whether North American or Asian lung flukes occur or could become established in mitten crabs within the San Francisco Estuary and associated watershed. No lung flukes have been found in the 500 adults examined, however, juvenile crabs and other crustaceans have not been examined.

Understanding Reproductive Development of the Chinese Mitten Crab

pp. 13-16. Tsukimura and Toste describe their work to develop indicators of reproductive state in mitten crabs. Understanding the processes that regulate the onset of reproduction could lead to identification of the stimulus (e.g., water temperature or day length) initiating downstream migration of crabs. If these stimuli can be monitored or predicted, it may be possible to anticipate the onslaught of migrating crabs, which could minimize the crab's threat to fish salvage operations at the SWP and CVP.

Water Quality Results from San Francisco Bay

pp. 17-20. Buchanan presents times series data of specific conductance, water temperature, and water level collected at seven sites in San Francisco Bay during water year 1999. Graphical results show tidal variability (ebb and flood) and seasonal differences strongly influence these data.

The Benefits of Floodplain Habitat to Rearing Chinook Salmon

pp. 26-30. Sommer and others present results of a study comparing the value of floodplain and riverine habitats to rearing chinook salmon. Study results indicate that salmon rearing on the Yolo Bypass floodplain have better growth, feeding success and perhaps survival than those which migrate through the heavily channelized Sacramento River. Results from these sorts of studies can help determine priorities for habitat restoration in the estuary.

Primary Food Resources in the Delta

pp. 21-25. Jassby and Cloern present a summary from their work examining the quantitative importance of different organic matter sources and some of the factors affecting temporal and spatial variability. Differences among sources were found among water years and seasons. Spatial heterogeneity implies that the relative importance of various sources will differ among subregions of the Delta. The results demonstrate that flow management has profound effects on the supply of organic matter to Suisun Bay, an important nursery area for larval fish. Moreover, these results underscore the need to obtain a better understanding of Delta ecology and the underlying processes to help guide the substantial restoration efforts contemplated for the Delta.

Monitoring the Distribution and Migration of Delta Smelt Using a Midwater Trawl

pp. 31-36. Gartz reviews the DFG midwater trawl (MWT) survey and its ability to provide useful information about the abundance, distribution, and spawning migration of delta smelt. This article provides a thoughtful discussion about the limitations of the MWT survey and the challenges to addressing those limitations. The article concludes with several recommendations for changes to this survey.

Largemouth Bass Fishery in the Delta

pp. 37-40. Analyzing tournament data from 1985-1999, Lee shows a remarkable increase in the number of bass tournaments and angler effort devoted to catching bass in the Delta over the last 15 years. The Delta Bass fishery has shown improvements not demonstrated by other California black bass fisheries. This article clearly demonstrates that other fishes besides the natives (delta smelt, salmon, and splittail) we hear so much about are also important.

Estimating Population Level Effects on Salmon and Estuarine Species

pp. 41-54. Miller presents a provocative article describing methods for estimating the population effects of changes in river flows and Delta water project operations on several important species of fish. Such approaches could have application in estimating the benefits of using water from an environmental water account or other actions to mitigate the impacts of water project operations.

Standardized Terms for IEP Publications:
A Hindrance or Help for Communicating the Value of IEP Work?

Regarding Wim Kimmerer's suggestions for standardized communications in the IEP Newsletter (spring 2000 issue): I concur with Wim about using the terms, "San Francisco Estuary" and "Sacramento-San Joaquin Delta." However, I do not agree that the IEP Newsletter should use metric units. Wim argues that the IEP Newsletter and IEP technical reports are about scientific issues and that the language of science includes a common system of units which is entirely metric.

I think Wim is going in the wrong direction with that suggestion. I do not think the IEP Newsletter or technical reports have a problem of not being scientific enough. Their problem is the opposite--about 80% of the IEP's funds come from the state and federal water projects. These projects are interested in information that is timely and relevant to the problems of the San Francisco Estuary in general and the Sacramento-San Joaquin Delta in particular. The IEP is doing a progressively better job of satisfying that need.

Randy Brown's "Of Interest to Managers" inside the front cover is a big step in the right direction. I would like to see even more emphasis on the management relevance of IEP work, and that emphasis appears to be forthcoming.

I would argue that the Newsletter's departure from the normal rules of scientific publications is what makes it so valuable. Information is timely. Ideas can be presented and then debated in later issues. And, we don't have to convert the numbers to another language. (Incidentally, when Ron Robie was DWR Director, there was an attempt to go metric. It did not work.)

If we have to use metric units to gain scientific respectability (the appropriate amount of which I do not believe is lacking), then follow the English units with metric units in parentheses, but please don't start producing graphs that require all of us to convert to acre-feet or cubic feet per second before we can appreciate their relevance.

William J. (B.J.) Miller, Consulting Engineer

Bloom Detected in Stockton Ship Channel

Scott Waller, DWR
swaller@water.ca.gov

Bay-Delta Monitoring and Analysis Section staff detected a brief and moderately intense phytoplankton bloom in the Stockton Ship Channel in the eastern Delta on May 22. The bloom was located in the vicinity of the multi-parameter recording station in the San Joaquin River at Burns Cutoff, near the western end of Rough and Ready Island.

Staff conducted a follow-up study of the central and southern Delta on May 25 to further clarify the extent and intensity of the bloom. The bloom extended from the San Joaquin River at Buckley Cove to the Stockton Yacht Harbor at the extreme eastern end of the Stockton Ship Channel and consisted of several phytoplankton taxon, with Cryptomonas being the most dominant organism. Other taxa present included Thalassiosira eccentrica, Aphanizomenon flos-aquae, Cosinodiscus, and an unidentified flagellated green algae.

Water quality was also evaluated in the bloom area to characterize conditions. Surface water temperatures ranged from 23.2 °C in the San Joaquin River at Channel Point to 25.1 °C at the Stockton Yacht Harbor. Fluorometric values ranged from 42.4 fluorescence units at the Stockton Turning Basin to 146.2 fluorescence units at the Stockton Yacht Harbor. The spectrophotometric values of chlorophyll a and pheophytin measured at the Stockton Yacht Harbor were 51 and 79.2 g/L, respectively, and were 26.7 and 21.1 g/L, respectively, at Channel Point. Nephelometric turbidity units (NTU) ranged from 6.2 NTU the Stockton Yacht Harbor to 10.6 NTU at the San Joaquin River at Buckley Cove. Finally, surface specific conductance values ranged from 413 S/cm at the end of the Stockton Yacht Harbor to 475 S/cm near the San Joaquin River at Buckley Cove.

Increased light intensity, warmer water temperatures and lower San Joaquin River inflows that typically occur during late spring and early summer may have been a stimulus for this bloom. The high production typical of the Stockton Turning Basin and Yacht Harbor may have also contributed to the introduction of the bloom into the San Joaquin River.

Neomysis and Zooplankton

Jim Orsi, DFG
jorsi@delta.dfg.ca.gov

As usual, the native Neomysis mercedis was not abundant during the spring. Highest abundance in April was slightly more than 1/m3 in the Suisun Marsh sloughs. Abundance was somewhat higher in May; the maximum was 10/m3 in the lower San Joaquin River and 8/m3 in Suisun Slough. The exotic Acanthomysis bowmani was much more abundant and reached 361/m3 at Martinez and 277/m3 in the low salinity zone.

As usual, the exotic Limnoithona tetraspina was the most abundant copepod, reaching highest concentrations in western Suisun Bay and in Carquinez Strait. The maximum was about 157,000/m3 at Martinez in May. Eurytemora affinis was widely distributed but did not exceed more than a few hundred per cubic meter at any location. The exotic Pseudodiaptomus forbesi was also widely distributed and more abundant than E. affinis. It reached a maximum abundance of about 2,500/m3 in Disappointment Slough. The native Diaptomus and Cyclops and the exotic Sinocalanus doerrii were not abundant but the native Acartia reached more than 35,000/m3 in Carquinez Strait. This is the highest seen in several years. Cladocerans were not abundant except in the San Joaquin River at Stockton in April. Rotifers were only moderately abundant.

Delta Smelt

Andy Rockriver and Michael Dege, DFG
arockriv@delta.dfg.ca.gov, mdege@delta.dfg.ca.gov

A special delta smelt vertical migration study was conducted on April 26-27, 2000, near Jersey Point on the San Joaquin River. Larval fish were sampled at three discrete depths using 0.5 m diameter conical plankton nets: one net was towed at the surface, one towed halfway to the bottom, and one towed near the bottom. Ninety samples were collected over a 17-hour period. To date, less than half of the samples have been processed. It appears larval osmerid densities were low. Preliminary results suggest there was a slightly higher catch of osmerids at the mid-depth than at the surface or bottom. Three times as many smelt were caught at night than during the day, and there seems to be no difference in catch between tides. The final data analysis will be completed this fall.

In May and June, high delta smelt densities near the CVP and SWP Delta export facilities resulted in the "red light" take limit being exceeded. Densities began to decline towards the end of June. To determine the "real time" distribution of delta smelt, three extra surveys (special surveys) were added to the normal 20-mm Survey. This resulted in weekly 20-mm Survey data from May through the middle of June.

Juvenile delta smelt monitoring by the 20-mm Survey has conducted 10 surveys (7 scheduled and 3 additional) through the middle of June. Preliminary results suggest minor spawning occurred in the central and southern Delta (surveys 1 and 2) and increased throughout the Delta (surveys through 6). Although the initial spawning was indicative of a wet year, catch from the latter surveys shows a trend similar to that of a dry year. Spawning incidence could be attributed to fluctuations in water temperature. High delta smelt densities (>1,000 fish per 10,000 m3) appeared in June around the confluence. For additional information, access our website at http://www.delta.dfg.ca.gov/data/20mm/2000.

North Bay Aqueduct larval fish sampling continues. The lab processing of these samples is lagging by several weeks due to the higher priority of processing 20-mm Survey samples. It appears some delta smelt spawned in the north Delta. So far this year, we caught more delta smelt (274) than the last two years combined (54). More than 75% of the delta smelt larvae were from the stations around Prospect Island. Several delta smelt were caught in Barker Slough in April and May of this year, compared to none in the past two years. Wakasagi numbers are also much higher than previous years, access our website at http://www.delta.dfg.ca.gov/data/nba/2000 for more information.

Real Time Monitoring

Robert Vincik, DFG
rvincik@delta.dfg.ca.gov

The Real-time Monitoring (RTM) program is approaching the end of the 2000 season. Monitoring began in late March and will finish June 30. Kodiak trawling at Mossdale continues as one of three maintained sites for the RTM 2000 survey. Trawling effort began on April 3 and will continue five days per week until June 30. Midwater trawls at Sherwood Harbor (Sacramento) and Chipps Island have been reduced to three days per week due to low tagged salmon catches, and increased numbers of delta smelt. This year RTM provided additional 20-mm surveys (special surveys 10, 11, and 12) which were conducted the weeks of May 7, 22, and June 5. Data from these surveys can be found at http://www.delta.dfg.ca.gov/data/20mm/2000/.

Light trapping for larval delta smelt began in March and continued through the first week in May. Surveys were conducted in Victoria Canal, Old River above Clifton Court, Miner and Cache sloughs, Old River at Frank's Tract, Turner and Columbia cuts, Grant Line canal, the North and South forks of the Mokelumne, Connection and Threemile sloughs, Empire Cut, Mandeville Tip, and Decker Island. The first delta smelt larvae were collected on April 6 in Turner cut. The largest concentration of delta smelt larvae were collected on April 20 in Victoria Canal and the Old River site above Clifton Court. Light trapping found post-hatch delta smelt distributed primarily in the central and south Delta.

Data from RTM light trapping, Kodiak and midwater trawling, 20-mm Survey, the spring midwater trawl and the federal beach seine surveys are available at the DFG website at http://www.delta.dfg.ca.gov/.

Delta Flow Measurement

Richard N. Oltmann, USGS
rnoltman@usgs.gov

The twelve stations of the continuous flow-monitoring network collected data throughout the quarter without extended periods of missing data, except for the Threemile Slough station. As reported last quarter, the attempt to calibrate the SL-ADCP at Threemile Slough was not successful, therefore, on May 10th, a UVM was reinstalled at the site. Several sets of flow measurements will be made during June and July to flow calibrate the new UVM.

Tidal and daily flow data from the UVM and SL-ADCP stations should become available in near real time during next quarter from a website under development by the USGS. This new website will also have a link to the new hydrodynamics database, also being developed by the USGS. The new database will replace the old FORTRAN-based database that has been in use for the last 15 years or so, and will contain historical UVM and UL-ADCP flow and stage data, plus assorted other data for the Delta and Bay.

Splittail Investigations

Randall Baxter, DFG
rbaxter@delta.dfg.ca.gov

The quarter began with hiring Scientific Aids and preparing for field sampling. The quarter ended with preliminary sampling and modest changes to our approach for habitat measurement in our study of age-0 splittail habitat use in the Sacramento River. Initial plans to use a differentially corrected GPS (DGPS) to measure habitat area were bolstered by the recent elimination of selective availability (intentionally introduced error in the satellite clocks that reduced location accuracy), but in practice, errors in accuracy were still 5 to 10 m, too high for this study. Instead, we will (1) use DGPS to locate habitat center-points, (2) record range and bearing to habitat boundary points, and (3) map and calculate surface area of each habitat in ArcView. Preliminary fieldwork indicates a good splittail year class despite the abrupt reduction in March outflow that drained most floodplains. We expect year-class size is sufficient to allow detection of differences in habitat use. One indication of a good year class occurred the first day of field training when over 300 age-0 splittail were captured in a single 15-m beach seine haul. Fieldwork will continue through September.

Microsoft Access queries were completed to calculate age-specific splittail abundance indices for Bay Study otter and midwater trawl data, USFWS beach seine and Chipps Island data. This should reduce the time necessary to produce these indices in the future, barring any significant modifications to any of the databases.

Juvenile Salmon Monitoring

Rick Burmester, USFWS
rburmest@delta.dfg.ca.gov

Seining at the lower Sacramento River sites collected 110 fall/spring run. The north, central, and south Delta catches included 590 fall/spring run. The San Joaquin River beach seine captured 39 fall run chinook, and the San Francisco Bay area beach seine caught one fall run on April 3 at Paradise Beach. Beach seine catches of juvenile chinook were down from those during the January through March 2000 period.

At Sacramento, the midwater trawl captured 2,691 fall/spring run. Kodiak trawling at Mossdale continued with DFG, Region 4 conducting the sampling. A total of 1036 chinook was captured. Midwater trawling at Chipps Island captured 17,761 fall/spring run and 50 winter run with the last one collected on May 20. The high Chipps Island fall/spring numbers were partly a result of double effort (20 tows per day) between April 16 and May 20 as part of increased tag recovery efforts for VAMP studies. While no late-fall run were captured in the trawls and winter run numbers declined, numbers of fall/spring run were lower than the previous quarter only at Sacramento. Mossdale fall run catches increased by 681 and Chipps Island fall/spring numbers were 17,658 greater than the previous quarter.

Catches of wild (non-adipose-clip) steelhead increased from the first quarter of the year, most of these were at Chipps Island where 41 steelhead were captured (181 to 447 mm). The Sacramento midwater trawl captured one steelhead at 215 mm, and three were captured in the Mossdale Kodiak trawl between April 7 and April 21 (240 to 287 mm).

This year, the Delta sub-team of the Salmon PWT is conducting a thorough review of the Delta Juvenile Salmon Monitoring Program and a report is expected soon. Several additional sampling efforts are recommended, such as year-round trawling at Mossdale, and a doubling of effort in the Delta and lower Sacramento River beach seines during the winter months. In addition, several cutbacks may be recommended, such as a reduction in effort of the midwater trawl at Sacramento during the spring.

For a review of the 1999-2000 Delta fisheries data, access the USFW- Stockton monitoring summary report at http://165.235.108.8/usfws/monitoring/report.asp.

Spring Midwater Trawl Survey, Midsummer Townet Survey, and Fall Midwater Trawl Survey

Russ Gartz, DFG
rgartz@delta.dfg.ca.gov

The Spring Midwater Trawl (SMWT) survey monitored the distribution and abundance of delta smelt (Hypomesus transpacificus) from January to March 2000. Results indicated that delta smelt were primarily located in Suisun Bay and Montezuma Slough. Monitoring was considered adequate despite the limitations of the gear and boat breakdowns in January.

The 2000 Midsummer Townet Survey (TNS) started on Friday, June 23, maintaining the continuity of the longest running survey in the Sacramento-San Joaquin Estuary. Results from the survey will be available on the Internet by late August or early September.

Rock Slough Monitoring Program

Jerry Morinaka, DFG
jmorinak@delta.dfg.ca.gov

A sieve-net was used to sample fish entrainment once a week at the Rock Slough intake of the Contra Costa Canal in April, May, and early June. The only fish captured in the sieve-net were three chinook salmon (Oncorhynchus tshawytscha) on May 3. All three salmon were within the fall-run size category for chinook salmon. Sampling was discontinued from May 8 to 22 due to a no diversion period at all of the Contra Costa Water District intakes. The sieve-net sampling will be discontinued in the late summer when the early phases of construction of the new fish screen facility begin at the Rock Slough intake. Fish entrainment sampling will resume when the initial construction period ends.

Old River Fish Screen Facility
(Los Vaqueros) Monitoring Program

Jerry Morinaka, DFG
jmorinak@delta.dfg.ca.gov

A sieve-net was used to sample fish entrainment three times a week behind the fish screens at the Old River Fish Screen Facility in April, May, and early June. The only fish captured in April were those that were entrained at the larval stage and had grown up within the facility. Sampling was discontinued from May 8 to 22 due to a no diversion period at all of the Contra Costa Water District intakes. Although only a few larval fish were entrained in May, large numbers of larval fish were entrained in early June. Striped bass, Morone saxatilis (mean fork length 10 mm), was the predominant larval fish species captured in the sieve-net in June. One delta smelt, Hypomesus transpacificus (18 mm FL) captured on June 2 was the first delta smelt captured behind the fish screens since inception of the facility. An egg and larval net was also used to sample fish entrainment behind the fish screen starting in June; however, very few fish have been captured in the net.

San Francisco Bay Fisheries Monitoring

Kathy Hieb, DFG
khieb@delta.dfg.ca.gov

The IEP, through DFG's San Francisco Bay Study, has been monitoring the abundance and distribution of fishes and macroinvertebrates in the Bay since 1980. Spring catches are a preliminary indication of year class strength for many species, although we typically use at least six month's data to calculate annual abundance indices. Age-0 longfin smelt catches from April through June 2000 were relatively low for the study period, with a total catch of 280. By comparison, we collected 1350 age-0 longfin smelt during the same months last year. However, catches have been much lower, with less than 100 age-0 longfin smelt collected annually from 1988 to 1992. In 2000, age-0 longfin smelt were distributed from Central San Francisco to Suisun bays, with the highest catches in Central San Francisco Bay in May and Central San Francisco and San Pablo bays in June.

Age-0 Pacific herring catches from April through June 2000 were the highest since 1993. (Note that in 1994 we dropped the midwater trawl from our survey after April.) With over 4,100 age-0 fish, the year 2000 catch was approximately seven times greater than either the 1998 or 1999 catches. The early cohort reported in the previous highlights article was still present in April, with fish from 65 to 80 mm FL. Fish from this cohort have been aged by Mike O'Farrell, a San Francisco State University graduate student. His preliminary analyses indicate spawn dates of October 20, 1999, and early November, which is very early for this species. Most age-0 Pacific herring were collected from northern South Bay and Central Bay, with a few fish as far upstream as Suisun Bay.

The first age-0 Dungeness crabs were collected in May, with a May-June total of 122 crabs. This is slightly higher than the 1999 May-June catch of 90 crabs; the 1999 age-0 index was the highest since 1988, which had an exceptional year class. In May 2000, age-0 Dungeness crabs were concentrated in the channel from northern South Bay to lower San Pablo Bay, but by June, they were dispersed over the shoals and collected from south of the Dumbarton Bridge to upper San Pablo Bay.

In contrast to the apparent revival of several cold water species, such as Pacific herring and Dungeness crab, our catches of some subtropical species, such as Pacific sardine, have declined. To date, we have collected only two Pacific sardine in 2000, compared to 831 fish during the same period in 1999. Also, no age-0 California halibut have been collected in 2000; in the first six months of 1999, we collected over 200 age-0 fish. The strong La Niña of 1999 dissipated in early 2000 on the West Coast, as sea surface temperatures have been near or slightly above average since January. Access the NOAA El Niño Watch website (http://cwatchwc.ucsd.edu/elnino.html) for more information about West Coast ocean conditions.

Adult Striped Bass Monitoring

Nina Kogut, DFG
nkogut@delta.dfg.ca.gov

Biennial tagging of legal-sized striped bass (>42 cm FL) was performed this spring. Striped bass were captured with two gill-netting boats in the western Delta (April 3 to June 1) and nine fyke traps in the Sacramento River near Knights Landing (April 19 to June 16).

We tagged 11,070 striped bass, the most since 1974. Before 1982, the legal size limit was 38 cm FL. If tagging had included fish from 38 to 41 cm FL this year, the total would have been approximately 12,671 compared to 13,785 in 1974. The number of striped bass tagged in the 1990s ranged from 4,612 (5,426 with 38 to 41 cm FL) in 1992 to 8,375 (9,821 with 38 to 41 cm FL) in 1991. In the 1980s, the highest number tagged was 7,403 (7,868 with 38 to 41 cm FL) in 1985. From 1969 to 1979, the number tagged ranged from 4,253 in 1978 to 18,377 in 1972 (>38 cm FL).

Of 11,908 legal-sized striped bass observed this spring, only 30 were recaptures from previous years. Twenty-nine were from the last tagging in 1998, and one was tagged in 1994. Coded-wire tags from net-pen-reared fish released into San Pablo Bay as yearlings or two-year-olds were found in 2.7% of the sublegal fish and 2.5% of the legal fish. The last time we tagged striped bass, in 1998, coded-wire tags were found in 0.8% of the sublegal fish and 2.4% of the legal fish.

This year's catch appears to have been dominated by three- and four-year-old striped bass (ca. 42-60 cm FL; 1997 and 1996 year classes), but an estimate of the actual age composition and abundance must await age determination of the tagged fish. The apparent high abundance of these year classes was not observed in the townet or midwater trawl surveys; however, the abundance is consistent with generally favorable estuarine hydrology.

Salmonid catch during striped bass tagging in 2000 included 51 adult chinook salmon and 17 adult steelhead. Forty-eight of the salmon were bright and likely to be spring run; the other three were more mature and were probably winter run. At least ten of the steelhead were hatchery-produced fish, as evidenced by adipose fin clips. These results compare with recent adult chinook salmon catches of 13 in 1998, when only the gill nets were fished, and 26 in 1996. Steelhead were not formally recorded before 2000.

Developing a Key for Larval Osmerids

Lenny Grimaldo, DWR; Lisa Lynch, DFG;
Johnson Wang, National Environmental Sciences;
and Brent Bridges, USBR
lgrimald@water.ca.gov

Wakasagi larvae were successfully cultured from an adult stock collected from San Luis Reservoir. Wild wakasagi larvae were also collected from San Luis Reservoir. A portion of the wild collected larvae was confirmed as wakasagi through genetic analyses. Over the next several months, we will document the variability of hatchery and wild wakasagi larvae using morphometric analyses. These characteristics will be compared with those of delta smelt larvae cultured and supplied by the Delta Smelt Culture Project. Additional wild specimens of delta smelt will need to be collected in 2001. Once enough specimens are collected we will begin to validate the key through a series of blind assessment trials with trained and untrained personnel.

Identifying the Trophic Structure and Carbon Sources of Fishes in Tidal Wetlands of the Sacramento-San Joaquin Delta

Lenny Grimaldo, DWR
lgrimald@water.ca.gov

The purpose of this project is to elucidate the trophic structure and source of organic matter that is ultimately assimilated by fishes along littoral zone (e.g., intertidal and subtidal habitats) and open water habitats (channel and deep subtidal) using stable isotope analysis. I anticipate this project will provide baseline information on how energy flows between primary producers and fishes in the Delta. Macrophyte, phytoplankton, invertebrate, and fish samples were collected at Mildred Island, Venice Cut Island, and Sherman Lake earlier this year. Over the next few months I will continue collections at these sites. Laboratory work will begin in August.

Exposure of Delta Smelt to Dissolved Pesticides

Kathryn Kuivila, USGS
kkuivila@usgs.gov

This project is measuring the exposure of delta smelt to dissolved pesticides during egg, larval, and juvenile stages for the third year. Sampling began at the end of April with water collected at six Delta sites every two weeks (coinciding with DFG's 20-mm sampling) and analyzed for dissolved pesticides. In addition, periodic "burst" sampling is being conducted in Montezuma Slough to establish a pesticide-salinity relationship over time. Study results for 1998 and 1999 will be presented in an IEP Newsletter article being planned for the fall 2000 issue.

Knights Landing Juvenile Salmonid Monitoring

Bill Snider, DFG
bsnider@dfg2.ca.gov

Juvenile salmonid emigration monitoring at Knights Landing continued through the spring period, April through June 2000. Juvenile salmon and steelhead catches at Knights Landing fell to zero during the latter part of this period marking the end of the primary migration season. Salmon emigration essentially ended during the week of June 12. Steelhead emigration ceased over a month earlier in mid-April.

During the quarter, we captured 794 fall-run sized, 41 spring-run sized, 10 winter-run sized and 3 late-fall-run-sized chinook salmon. Nearly all of these salmon were collected during April, immediately following the first large release of Coleman National Fish Hatchery (CNFH), produced fall run into the upper Sacramento River. As observed during the past four years, the last catches of steelhead, and winter-run and late-fall-run chinook salmon at Knights Landing are associated with the first, large release of CNFH salmon. Seven steelhead, three late-fall run and nine winter run were captured at Knights Landing shortly after the CNFH release, while no steelhead, late-fall or winter-run salmon were collected for at least four weeks prior.

Overall, catches of both salmon and steelhead were low during the 1999-2000 season, less than half of the mean catch (about 60,000 salmon) observed during the first four years of monitoring at Knights Landing. Altogether, we collected 23,531 salmon and 38 steelhead, including 23,435 fall-run, 185 spring-run, 75 winter-run, 45 late-fall-run and 60 adipose-clipped salmon, and 27 adipose-clipped steelhead.

Sherman Island Agricultural Diversion Evaluation

Matt Nobriga DWR
mnobriga@water.ca.gov

This element will compare the relative abundance and species composition of fishes entrained in side by side diversion siphons (one screened, one not screened) in Horseshoe Bend on the lower Sacramento River. The siphons are being sampled using modified fyke nets (1600-m mesh) that sample all of the water coming through the siphons. We are planning to do a continuous 48-hour sampling blitz (consisting of hourly samples) from water being diverted through both the screened and unscreened siphons simultaneously. This initial field work will take place sometime during the first two weeks of July, but the specific dates have not been set.

Upper Estuary Chinese Mitten Crab Research Projects

Tanya Veldhuizen and Cindy Messer, DWR
tanyav@water.ca.gov, cmesser@water.ca.gov

Few Chinese mitten crabs have been collected in the Sacramento-San Joaquin Delta this year, although mitten crabs remain very abundant in South Bay tributaries. Mitten crab catch for the Chinese Mitten Crab Habitat Use Study remains low with only three crabs collected since February. Alternative sampling methods (for example, burrow excavation, beach seine, and modified crab scrape) will be explored in July and August.

The Mitten Crab Benthos Impact Study also has collected few mitten crabs. Sampling began in late April and has consisted of monthly otter trawls at nine stations. These stations are part of DWR's historical benthic monitoring stations. Data obtained from these initial trawls will be used to determine the presence of mitten crabs at the stations. Two crabs have been collected to date, one 46-mm male crab was collected in Suisun Bay near Martinez (D6), and a second 57-mm male crab was collected in the Sacramento River at Collinsville (D4). Both crabs were collected on May 18. A 425 mm green sturgeon, Acipenser medirostris, was also collected at D4 on May 18.

Interestingly, an age-0 crab (4 to 5 mm CW) was collected in the Yolo Bypass toe-drain in June. The crab was found amongst leaves in the rotary screw trap located 14.5 river miles upstream of the bypass confluence with the Sacramento River near Rio Vista.

Delta Smelt Culture Update

Bradd Baskerville-Bridges and Joan Lindberg
University of California, Department of Animal Sciences
(209) 839-0752, bridges@tracy.com

Nearly 120,000 eggs were collected this season, yielding over 50,000 larvae. Most of the eggs were spawned during March and April, while temperatures were still cool. Smelt in the outdoor tanks (natural lighting) started spawning earlier and produced nearly twice as many eggs as fish from the indoor tanks (dim artificial lighting). As the outside temperature rose during May and June, water flows had to be reduced in all tanks. This was done to maintain 16 to 18 °C and may account for the reduced spawning activity during this time.

The smelt culture facility is now equipped with three recirculation systems fur use in larval/juvenile research. Experiments are still in progress to investigate the effect of stocking density (20, 40, and 80 larvae/L) and temperature (14 °C, 17 °C, and 20 °C) on growth and survival of smelt larvae. In addition, small-scale studies are being performed to follow up on last years feeding behavior experiments.

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Davis GM, Chen CE, Kang ZB, Lui YY. 1994. Snail hosts of Paragonimus in Asia and the Americas. Biomedical and Environmental Sciences 7:369-82.

Li YS. 1989. A survey of freshwater crabs harbouring parasites in Fujian Province. Acta Hydrobiologica Sinica 13:83-6.

Lou YS, Fujino T, Morita K, Ishii Y. 1992. A comparative ultrastructural and histochemical study of the metacercarial cyst walls of four species of Paragonimus. Parasitology Research 78:457-462.

Miyazaki I, Chiu JK. 1980. Examination of the so-called Paragonimus westermani in Taiwan. Medical Bulletin of the Fukuoka University 7:277-79.

Yokogawa M. 1965. Paragonimus and Paragonimiasis. Advances in Parasitology 3:99-158.

Yokogawa S, Cort WW, Yokogawa M. 1960. Paragonimus and Paragonimiasis. Experimental Parasitology 10:81-137, 139-205.

Notes

Mark Torchin. Marine Science Institute, University of California, Santa Barbara. Personal conversation with author on January 10, 1998.

Reproduction in the Chinese Mitten Crab, Eriocheir sinensis

Brian Tsukimura and Angela Toste, Department of Biology, California State University, Fresno
BrianT@CSUFresno.edu

Introduction

Since the 1992 discovery of the Chinese mitten crab, Eriocheir sinensis (Decapoda: Brachyura) in the South San Francisco Bay, their population has expanded into the Sacramento-San Joaquin Delta system and watershed (Veldhuizen and Hieb 1998). The juvenile crabs migrate into freshwater areas where they develop into adults. In California, these crabs now range from as far north as Colusa, east to Marysville, and south to San Luis National Wildlife Refuge in Merced County (Veldhuizen and Stanish 1999). Towards the end of summer, the crabs start their seaward migration to spawn. This migration has caused much concern for the U.S. Bureau of Reclamation's Tracy Fish Recovery Facility and the Department of Water Resources Skinner Fish Recovery Facility. Issues of concern involve the loss of endangered fish species and curtailment of water pumping. During the late summer, the crab's reproductive system begins to mature. It is unknown whether the downstream migration and reproductive events are linked to a single environmental or physiological stimulus or initiated by separate stimuli.

Understanding the stimulus that initiates reproduction is critical for the development of plans that could minimize the adverse effects of the mitten crab on the estuary system, and fish and water facilities. Water temperature and day length are probable cues for stimulating reproduction in these crabs. Understanding the environmental parameters that regulate the onset of reproductive processes can provide a mechanism that will enable water managers to anticipate the onslaught of downstream migrating crabs. These data might allow monitoring water temperature and day length to predict the downstream migration of the crabs.

To initiate studies on reproduction of the mitten crab, we determined the gonadosomatic index (GSI) of downstream migrating females. These data provide a baseline against which annual comparisons can be made. To facilitate examination of reproduction, identification of a biological marker is required. Yolk, also known as vitellin, is an obvious choice for a biological marker because it composes the greatest volume of the egg. Thus, the synthesis of yolk proteins is a good indicator of female reproductive activity. (See reviews in Charniaux-Cotton 1985; Meusy and Payen 1988; Tsukimura submitted.) Furthermore, the presence of yolk proteins has been frequently used to study the environmental cues that appear to initiate reproduction.

Abbreviated Methods

Results and Discussion

From September through November, female crabs were of similar carapace width (mean = 66.3 mm; range: 59 to 78 mm carapace width) from the Tracy Fish Recovery Facility (Figure 1). The crabs in February were smaller than those in October, but not from September and November. Crabs collected in April were significantly smaller (mean carapace width = 55.1 mm) than those collected earlier. These smaller sized crabs, possessing developing ovaries and still non-ovigerous, were collected with many other ovigerous females, which may explain the size difference. These smaller crabs may take longer to reach the higher salinity waters that are required for final ovarian maturation. The crabs from Tracy BOR were similar in size to downstream migrating mitten crabs reported in France (42 to 74 mm) (Hoestlandt 1948), but larger than those reported for fourth- and fifth-year crabs (38 to 50 mm) in other regions of Europe (Ingle 1986).

1. Mean carapace width for female Eriocheir sinensis collected at the Tracy Fish Recovery Facility. Fall sizes are similar, whereas differences occur in later months. The smaller females may require more time to descend from their freshwater habitats. Data were analyzed using one-way ANOVA (+ Tukey's Test). Means followed by the same letter are not significantly different (p < 0.05). "n" indicates number of individuals examined. Note that April animals were collected downstream of Tracy and were significantly smaller than earlier months. These crabs were not yet ovigerous, but were collected when many larger crabs were already ovigerous.

Female mitten crabs migrating downstream in September had lower GSI (4.5%) than all female crabs in successive months (7.8%), except for April (Figure 2). Because the carapace sizes of these crabs are similar, the smaller GSI appears to reflect these crabs' earlier reproductive development in comparison to crabs collected in later months. Only three non-ovigerous females were collected in April with a wide range of GSI data (3.6% to 12.8%). Data from France indicate that developing oocytes are common in downstream migrating mitten crabs (Hoestlandt 1948). The completion of ovarian development occurs in brackish water (DeLeersnyder 1967), thus it would not be expected that animals with significantly larger GSI would be found at Tracy.

1. Mean GSI for female Eriocheir sinensis collected at the Tracy Fish Recovery Facility. Females caught in September had significantly lower GSI than the successive months. Data were analyzed using one-way ANOVA (+ Tukey's Test). Means followed by the same letter are not significantly different (p < 0.05). "n" indicates number of individuals examined.

Upon purification of the Vn, the protein was analyzed by HPLC column chromatography and determined to be 618 kDa in molecular mass. This size is large compared to the known molecular mass for other crabs (Tsukimura submitted). For example, the Vn of the green crab, Carcinus maenas, has a molecular mass of 480 kDa (Andrieux and deFrescheville 1992), and Potamon potamias Vn has a molecular mass of 551 kDa (Pateraki and Stratakis 1997). Under denaturing conditions, E. sinensis Vn consists of four subunits (111 kDa, 112 kDa, 127 kDa and 135 kDa) (Figure 3). In other crabs, Vn is composed of two to four subunits (with molecular mass ranging from 39 to 188 kDa) (Tsukimura submitted). Eriocheir japonica has two subunits (Komatsu and Ando, 1992). Other crabs with two Vn subunits are: the green crab, Carcinus maenas, (Andrieux and de Frescheville 1992); Uca pugilator (Eastmen-Reks and Fingerman 1985); and Charybdis feriata (Komatsu and Ando 1992). In addition, the rock crab, Cancer antennarius, has three subunits (Lee and Puppione 1988; Spaziani 1988) and the blue crab, Callinectes sapidus, has four subunits (Lee and Watson 1995).

1. SDS-PAGE separation of Eriocheir sinensis vitellin (Vn) demonstrating the presence of four subunits, with sizes indicated. Molecular mass (MW) markers are shown on the right side.

We have developed and characterized an anti-Vn antiserum. Thus far we have found that the antisera only bind the four subunits of Vn when examining crude ovarian extracts and reproductive female hemolymph (data not shown). This makes it useful for the identification of yolk protein molecules from hemolymph samples. We are currently using this anti-Vn antiserum to develop an Enzyme-linked Immunosorbant Assay (ELISA) with which hemolymph levels of yolk proteins can be determined. We have previously collected hemolymph samples from mitten crabs last fall and winter that will be assayed for yolk protein levels. These data will then be compared to the GSI and carapace data to better assess the amount of ovarian development that is occurring in downstream migrating female mitten crabs.

During oocyte development, yolk proteins are synthesized both within the oocyte and often in the hepatopancreas, which is the crustacean equivalent to the liver (see review in Tsukimura submitted). The yolk is transported through the hemolymph to the oocytes where it is incorporated into the egg (Charniaux-Cotton 1985). Thus, the amount of yolk protein in the hemolymph is an indicator of reproductive progress, and at least, an indicator of gonadal development.

In summary, we have established a baseline GSI and size of downstream migrating female crabs at the Tracy Fish Recovery Facility. These data will be used to compare carapace sizes and GSI for fall 2000-winter 2001 crabs. In addition, we have purified and characterized the yolk protein of the mitten crab, then developed an anti-Vn antiserum. We will use this antiserum in an ELISA that will detect changes in yolk protein levels in hemolymph. This assay will be useful in examining environmental and physiological cues that stimulate ovarian development.

At the last annual meeting of the Society for Integrative and Comparative Biology where a crustacean physiology symposium was convened, much interest was generated about the presence of the Chinese mitten crab invasion of California. This is the only catadromous crab in North America. Many biologists were interested in the crab's physiological abilities to withstand salinity and temperature changes, as well as how the crab regulates molts and tissue growth. Although the full impact of this invasive species remains unknown, it is a useful organism to study basic crustacean biology.

References

Anderson SL, Clark WH, Chang ES. 1985. Multiple spawning and molt synchrony in a free spawning shrimp (Sicyonia ingentis: Penaeoidea). Biol Bull 168:377-94.

Andrieux and deFrescheville. 1992. Caratérization de la vitelline secondaire chez le Crustacé Brachyoure Carcinus maenas. CR Acad Sci Paris Ser III 314:227-30.

Charniaux-Cotton H. 1985. Vitellogenesis and its control in malacostracan crustacea. Am Zool 25(1):197-206.

De Leersnyder M. 1967. Influence de la salinité et l'ablation des pédoncles oculaires sur la mue et sur le développement ovarien d'Eriocheir sinensis H. Milne-Edwards. Cah Biol Mar 8:421-35.

Eastman-Reks SB, Fingerman M. 1985. In vitro synthesis of vitellin by the ovary of the fiddler crab Uca pugilator. J Exp Zool 233:111-6.

Hoestlandt H. 1948. Recherches sur la biologie de l'Eriocheir sinensis H. Milne-Edwards (Crustacé Brachyoure). Ann Inst Océanogr 24:1-116.

Ingle RW. 1986. The Chinese mitten crab Eriocheir sinensis H. Milne-Edwards--a contentious immigrant. Lond Naturalist 65:101-5.

Komatsu M, Ando S. 1992. Isolation of crustacean egg yolk lipoproteins by differential density gradient ultracentrifugation. Comp Biochem Physiol 103B:363-8.

Laemmli UK. 1970. Cleavage of structural proteins during the assembly of bacteriophage T4. Nature (London) 227:680-5.

Lee C-Y, Watson RD. 1995. In vitro study of vitellogenesis in the blue crab (Callinectes sapidus): Site and control of vitellin synthesis. J Exp Zool 271:364-72.

Lee RF, Puppione DL. 1988. Lipoproteins I and II from the hemolymph of the blue crab Callinectes sapidus: Lipoprotein II associated with vitellogenesis. J Exp Zool 248:278-89.

Meusy JJ, Payen GG. 1988. Female reproduction in malacostracan Crustacea. Zool Sci 5:217-65.

Pateraki LE, Stratakis E. 1997. Characterization of vitellogenin and vitellin from the land crab Potamon potamios: Identification of a precursor polypeptide in the molecule. J Exp Zool 279:597-608.

Riley LG, Tsukimura B. 1998. Yolk protein synthesis in the riceland tadpole shrimp, Triops longicaudatus, measured by in vitro incorporation of 3H-Leucine. J Exp Zool 182:238-47.

Spaziani E. 1988. Serum high density lipoprotein in the crab, Cancer antennarius Stimpson: II. Annual cycles. J Exp Zool 246:315-8.

Tsukimura B, Bender JS, Linder CJ. Developmental aspects of gonadal regulation in the ridgeback shrimp, Sicyonia ingentis. Submitted.

Tsukimura B. Crustacean vitellogenesis: Its role in oocyte development. American Zoologist. Submitted.

Veldhuizen T, Hieb K. 1998. What's new on the mitten crab front? IEP Newsletter 12(2):24-5.

Veldhuizen T, Stanish S. 1999. Overview of the life history, distribution, abundance, and impacts on the Chinese mitten crab, Eriocheir sinensis. Report prepared for the U.S. Fish and Wildlife Service. Sacramento (CA): California Department of Water Resources. 26 p.

Specific Conductance, Water Temperature, and Water Level Data from San Francisco Bay, California,
in Water Year 1999

Paul A. Buchanan, U.S. Geological Survey
(916) 278-3121, buchanan@usgs.gov

Introduction

This article presents time-series plots of specific-conductance, water-temperature, and water-level data collected at seven sites in San Francisco Bay during water year 1999 (October 1, 1998 through September 30, 1999). Specific conductance and water temperature data are recorded continuously at the following locations (Figure 1).

• Carquinez Strait at Carquinez Bridge
• Napa River at Mare Island Causeway near Vallejo
• San Pablo Bay at Petaluma River Channel Marker 9
• San Pablo Strait at Point San Pablo
• Central San Francisco Bay at Presidio Military Reservation
• Central San Francisco Bay at Pier 24
• South San Francisco Bay at San Mateo Bridge near Foster City

Water level data are recorded only at Point San Pablo. The data from Point San Pablo, Presidio, Pier 24, and San Mateo Bridge were recorded by the California Department of Water Resources (DWR) before 1988, by the U.S. Geological Survey (USGS) National Research Program from 1988 to 1989, and by the USGS-DWR cooperative program since 1990. The Carquinez Bridge, Napa River, and San Pablo Bay sites were established in 1998 by the USGS.

Data Collection

Typically, specific conductance and water temperature data were collected at near-surface and near-bottom depths in the water column to define the vertical stratification. However, at the more shallow San Pablo Bay and Presidio sites, data were collected only at near-bottom depth because the mean lower-low water depth was about six feet. The mean lower-low water depth is the average of the lower-low water height of each tidal day observed during the National Tidal Datum Epoch [the specific 19-year period (1960-1978) adopted by the National Ocean Service as the official time segment over which tide observations are taken and reduced to obtain mean values]. The San Mateo Bridge site was shut down in March 1999 for seismic retrofitting of the bridge and data collection is scheduled to resume in June 2000.

1. Location of specific conductance, water temperature and water level data continuous monitoring sites in San Francisco Bay, California

Specific conductance (reported at 25 °C) was measured using either a Foxboro electrochemical analyzer (calibrated accuracy 3%) or a Hydrolab Datasonde 4 multiprobe (conductivity cell calibrated accuracy 1%). Water temperature was measured using a Campbell Scientific thermister (accuracy 0.4°C) or the Hydrolab Datasonde 4 multiprobe (temperature probe accuracy 0.1°C). Water level was measured using a Handar incremental encoder with a float-driven, incremental, stainless steel tape. Specific conductance, water temperature, and water level measurements were made and data were stored every 15 minutes, controlled by a Campbell Scientific CR10 data logger or the Hydrolab Datasonde 4 multiprobe internal data logger.

Instrument calibrations were completed in the field every two to three weeks. Calibration of the continuous recording instruments measuring specific conductance was done using an Orion model 140 conductivity meter (calibrated accuracy 2%) calibrated to a known specific conductance standard. Calibration of the water temperature instruments was done using a VWR Scientific thermister (accuracy 0.2 °C). Water level instruments were checked using a wire-weight gage mounted to the pier at Point San Pablo. Data corrections (normally resulting from biological fouling), based on differences between the continuous-recording instrument readings and the field-calibrated instrument readings, were applied to the record for final computation using the USGS Automated Data Processing System.

Data Presentation

Figures 2 through 6 show time-series plots of the specific conductance, water temperature, and water-level data measured at the seven sites in San Francisco Bay. Tidal variability (ebb and flood) affects specific conductance, water temperature, and water level. In Figures 2 through 6, the degree of tidal variability corresponds with the vertical range of the "black bands," which is caused by compressing a year of time-series data into a small plot. To illustrate tidal variability, Figure 7 shows the near-surface and near-bottom specific conductance and water level at Point San Pablo for the 24 hours of December 25, 1998. Tidal variability was greater in San Pablo Bay than in South San Francisco Bay (Schoellhamer 1997). Gaps in the data usually are caused by equipment malfunctions.

Maximum and minimum values of specific conductance, water temperature, and water level data for the seven sites are published annually in volume 2 of the USGS California water data report series, which is available on the USGS website at http://water.wr.usgs.gov.

1. Near-surface (NS) and near-bottom (NB) measurements of specific conductance at Carquinez Bridge (CARQ), Napa River (NAP), Point San Pablo (PSP), and San Pablo Bay (SPB), San Francisco Bay, water year 1999. For reference, seawater has a specific conductance of 53,000 microSiemens per centimeter.

1. Near-surface (NS) and near-bottom (NB) measurements of specific conductance at San Mateo Bridge (SMB), Pier 24 (P24), and Presidio (PRES), San Francisco Bay, water year 1999. For reference, seawater has a specific conductance of 53,000 microSiemens per centimeter.

1. Near-surface (NS) and near-bottom (NB) measurements of water temperature at Carquinez Bridge (CARQ), Napa River (NAP), Point San Pablo (PSP) and San Pablo Bay (SPB), San Francisco Bay, water year 1999

1. Near-surface (NS) and near-bottom (NB) measurements of water temperature at San Mateo Bridge (SMB), Pier 24 (P24), and Presidio (PRES), San Francisco Bay, water year 1999

1. Water levels at Point San Pablo, San Francisco Bay, water year 1999. Vertical datum is 10 ft below sea level.

1. Near-surface and near-bottom measurements of specific conductance and water levels at Point San Pablo, San Francisco Bay on December 25, 1998. Vertical datum is 10 ft below sea level. For reference, seawater has a specific conductance of 53,000 S/cm.

References

Schoellhamer DH. 1997. Time series of SSC, salinity, temperature, and total mercury concentration in San Francisco Bay during water year 1996: 1996 Annual Report of the Regional Monitoring Program for Trace Substances. p 65-77.

Introduction

The Sacramento-San Joaquin River Delta, a complex mosaic of tidal freshwater habitats, is now a focus of ecosystem rehabilitation because of changes in critical functions associated with its geographic location at the land-estuary interface. One of these functions is the production, transport, and transformation of organic matter that constitutes the "primary food supply," that is, the food supply to the base of the food web. Interest in the primary food supply is motivated by evidence for sub-optimal food quantity or quality at trophic levels that support fish recruitment, including primary consumers such as clams, mysids, cladocerans, rotifers, and native copepods. We used the historical data set to examine the magnitudes of the most important organic matter sources for the Delta, the factors underlying their interannual and longer-term variability, and the implications of ecosystem rehabilitation actions for these sources. Here, we present a summary of the first phase of the analysis, including the quantitative importance of different organic matter sources and some of the hydrological controls on their year-to-year variability. The full report of this first phase-including data sources, the methods of calculation, and references, is in press elsewhere (Jassby and Cloern forthcoming). The historical data analysis is part of a larger project in which measurements of stable isotopes and biogeochemical markers, and experiments on organic matter biodegradation and zooplankton growth rates, are being used collectively to define the primary food resources and their quality.

Gross Organic Matter Sources

Organic matter sources in terms of total organic carbon (TOC) are summarized in Table 1. Comparisons are possible only on an average annual Delta-wide basis for most of these sources. Tributary-borne loading is the largest source overall. Phytoplankton production (estimated from a model that incorporates incident light, phytoplankton biomass, and water clarity) and agricultural drainage are secondary sources. Wastewater treatment plant discharge, marsh export, and possibly aquatic macrophyte production are tertiary sources. Benthic microalgal production, urban runoff and other sources not explicitly mentioned are negligible. Phytoplankton is clearly the dominant primary producer on a Delta-wide basis, whereas tributary-borne loading is dominant among the allochthonous (external) sources. The ratio of combined primary production to total sources is only 15%. It is important to note that these are sources for benthic habitat and water column combined. An accounting for the water column alone would have to isolate the supply of dissolved organic carbon (DOC) from the sediments. DOC can be a significant source for bacterioplankton production.

For most of the organic matter supply, sufficient data exist to compare based on season and water year classification. A water year extends from October 1 of the previous calendar year to September 30. Water years in the Sacramento River Basin are classified based on annual stream flow data into (1) wet, (2) above-normal, (3) below-normal, (4) dry, and (5) critical. We combined (1) and (2) into a category referred to as "above normal" and (3) to (5) into a category referred to as "below normal." For each category, we compared phytoplankton productivity and tributary-borne load, only for those years in which complete data are available for each of these sources. Agricultural drainage is also included, although we have had to assume that the amount is independent of year (Table 2).

Phytoplankton production, tributary-borne loading and agricultural drainage together account for 90% of total sources. In above normal years, tributary-borne loading is always dominant. Although phytoplankton productivity is small compared to agricultural drainage in winter, it is similar in autumn and much greater during spring and summer. A comparison among water year types shows, phytoplankton productivity increases in spring of below-normal years because of higher hydraulic residence time and the resulting accumulation of phytoplankton biomass. Tributary-borne loading, in contrast, decreases in below-normal years because of lower inflows. Consequently, the two sources are similar in magnitude. Even in summer of below-normal years, they differ by only a factor of two. The relative importance of sources is therefore clearly dependent on season and on the prevailing climate conditions.

Many of these sources are also distributed in a spatially heterogeneous manner. This diversity and heterogeneity implies that the relative importance of sources will change as we move from one Delta subregion to another. The aquatic vascular plant Egeria densa, for example, covered 35% of Franks Tract in September 1997. If we assume this level of coverage for the year and apply our phytoplankton productivity estimates from one station in Franks Tract to the remaining area, then annual Egeria and phytoplankton production are within 10% of each other. Similarly, much of the remaining tidal marsh habitat in the Delta is found in the western portion, and so tidal marsh export is bound to be more important in this region. In the San Joaquin River near Vernalis, large phytoplankton blooms occur, sometimes reaching chlorophyll a concentrations of over 50 g/L. Phytoplankton production is most likely the dominant organic matter source in this part of the Delta during spring and summer.

Net Organic Matter Sources

These sources differ in their availability to the food web, and a further refinement is necessary before they can be directly compared as food sources. Particulate organic carbon (POC) enters the Delta from allochthonous sources mostly as phytoplankton and phytoplankton-derived detritus, other microscopic detrital particles, microheterotrophs, and suspended mineral particles with adsorbed organic matter. It is not clear how much the latter form of POC participates in the food web. The remaining POC input immediately becomes part of the microscopic particle or microalgae pool; it should be just as available to the metazoan food web as particulate primary production. In contrast, allochthonous dissolved organic carbon (DOC) must go through an additional step before it becomes available to the metazoan food web (Figure 1). Conversion to POC does not guarantee incorporation into the metazoan food web, but at least it places DOC input on a par with microscopic food particles. It is essential to consider the losses during this step, because most of the allochthonous organic matter enters in dissolved form. In a similar vein, we must also correct gross primary productivity for losses due to phytoplankton respiration. Then we can more accurately compare allochthonous sources and primary production in terms of net food particle production. These corrections, detailed in the full manuscript, take into account (1) the proportion of DOC that is labile; (2) bacterial growth efficiency; (3) the ratio of DOC:TOC; and (4) a simple model for phytoplankton respiration that includes basal metabolism and photosynthesis-dependent losses.

When these losses are taken into account, the relative importance of organic matter sources changes dramatically (Table 3). Except for above-normal winters, net phytoplankton productivity is a significant source in all seasons. Moreover, phytoplankton productivity is comparable to and sometimes greater than tributary-borne loading in spring and summer of both above-normal and below-normal water years. Spring and summer are particularly critical seasons for larval development and recruitment success. In contrast, agricultural drainage is almost never significant.

1. A simplified model of organic carbon pools and flows in the Sacramento-San Joaquin Delta. The thick gray arrows represent exchange with the CO2 pool through photosynthesis or respiration. The dashed arrows represent flows of secondary significance.

Role of Allochthonous POC

The above considerations imply that tributary-borne DOC contributes little to the available supply. From the viewpoint of primary food sources, the main function of the tributaries is to deliver POC. What is the value of this allochthonous POC as food for primary consumers? Although we cannot characterize this POC completely, at times a large fraction appears to be phytoplankton and phytoplankton-derived detritus (Figure 2). Moreover, the supply of this river-borne phytoplankton material can sometimes compare with production within the Delta (Figure 3). Some of the remaining portion of the POC load is composed of nonliving organic detritus along with bacteria and other heterotrophs. Generally, the food value of detritus and bacteria is not as high as phytoplankton, and it is enhanced when supplied in combination with phytoplankton, which contains higher amounts of essential fatty acids and other substances. Phytoplankton-derived material is therefore important beyond its simple contribution to the total POC loading. A final portion of the POC load is organic matter adsorbed to mineral suspensoids. Clay-organic-bacteria aggregates can be important components of turbid systems. The concentration of POC on clay increases bacterial growth efficiency and the use of these aggregates directly by larger zooplankton bypasses the inefficient microzooplankton link of nanoflagellates and ciliates. While a large portion of the load may be in this form at times, its value for the food web remains unknown and it remains a major gap in our understanding of organic matter supply.

1. Phytoplankton-derived PON as a percentage of total organic N (TON) loading into the Delta, as a function of season and river flow. Note that the phytoplankton percentage of PON loading into the Delta must be even higher. Inset values: seasonal means ( standard error of the mean among years).

The Delta as a Transition Zone

Suisun Bay and the western Delta downstream of our boundary at Rio Vista-Twitchell is the site of an important larval fish nursery. The estuarine turbidity maximum with its unique biological characteristics and elevated POC is found in this downstream region. The Delta can be viewed as a kind of transformer, either attenuating or enhancing the mass loading from tributaries before discharging into this region and ultimately San Francisco Bay. What net effect does the Delta have on delivery of this material? We examine this question by comparing mass loading ratios for total organic nitrogen (TON) in wet versus critically dry water years. The wet and critically dry years were chosen for comparison because they are the extreme categories and because the necessary data are available.

1. Phytoplankton-derived POC loading into the Delta relative to phytoplankton productivity within the Delta, as a function of season and river inflow. Inset values: seasonal means ( standard error of the mean among years).

Table 4 demonstrates that, on the upstream side, the Sacramento River contributed most TON loading. Nonetheless, the San Joaquin River contributed 20% to 42% of the total on a seasonal basis, much higher than expected based on flow. The main difference of note between year types is the proportion flowing downstream--that is, the outflow:efflux ratio--in wet versus critical years. In critical years, the proportion of the efflux flowing out into the ecologically important area just downstream of the Delta drops by almost half. Only 24% to 47% of the TON, depending on the season, flows downstream into the Bay; the remaining 53% to 76% is exported from the Bay-Delta for use elsewhere.

Several points implied by the data of Table 4 require emphasis because of their ecological and management importance to Suisun Bay and the rest of San Francisco Bay downstream. First, the Delta can act as a net producer rather than net consumer of organic matter in critical years. Second, whether or not the Delta augments the supply of inflowing organic matter, enough is exported from the system so that organic matter outflow into the Bay is much less than inflow from tributaries to the Delta. Finally, even with losses to exports, organic matter loading from the Delta to Suisun Bay is still significant compared to sources within the Bay. For example, we previously estimated organic matter sources in Suisun Bay to be 3.9 T/d TON, exclusive of riverine loading. In the present study, we estimate the mean ( standard error of the mean) for riverine loading to Suisun Bay, i.e., outflow from the Delta, to be 17 4 T/d TON. Taken together, these points demonstrate that flow management has profound effects on the supply of organic matter to Suisun Bay and, therefore, the food supply for larval fish in this important nursery area.

Concluding Remarks

In general, the results demonstrate that the phytoplankton-derived organic matter supply, both from production within the Delta as well as from upstream loading, is much more important for food particle production than apparent from a simple accounting of organic carbon. Its importance is probably even greater than indicated by our quantitative analysis, for two reasons. First, even though DOC may be converted to bacterial biomass, the bacteria must be repackaged as larger particles before being consumed by many mesozooplankton. This may happen automatically if the bacteria are part of a clay-organic-bacteria aggregate, but otherwise requires consumption of bacteria by microzooplankton with attendant losses due to respiration. Second, recent research suggests primary consumers such as zooplankton may be limited by the availability of certain polyunsaturated fatty acids found in phytoplankton, not by energy or generic organic carbon. Insofar as this is true, bacteria and perhaps even the non-phytoplankton-derived organic carbon from upstream may be a relatively poor food source. In any case, as demonstrated in the full paper, restoration actions--including new canals, flow and fish barriers, increased use of floodplains, and increased shallow-water habitat--all have significant effects on phytoplankton production, some positive and some negative. Given the significance of phytoplankton production to the food base in the Delta, these effects must be defined quantitatively and used to help guide the restoration strategy.

Acknowledgments

This research was funded by CALFED (1425-98-AA-20-16240) and the U.S. Geological Survey. The senior author is also grateful for support from the U.S. Environmental Protection Agency (R819658) through the Center for Ecological Health Research at the University of California, Davis. Although the U.S. EPA partially funded preparation of this document, it does not necessarily reflect the views of the agency and no official endorsement should be inferred.

References

Jassby AD, Cloern JE. Organic matter sources and rehabilitation of the Sacramento-San Joaquin Delta (California, USA). Aquatic Conservation: Marine and Freshwater Ecosystems. Forthcoming.

Floodplain Rearing May Enhance Growth and Survival of Juvenile Chinook Salmon in the Sacramento River

Ted Sommer, Matt Nobriga, Bill Harrell, Wendy Batham, and Ryon Kurth, DWR; Wim Kimmerer, SFSU
tsommer@water.ca.gov

Although the trophic dynamics of large rivers are strongly affected by upstream inputs (Vannote and others 1980), there is increasing recognition that floodplain habitat plays a major role in the productivity and diversity of riverine communities (Junk and others 1989). Here we provide evidence that floodplain provides better habitat than adjacent river channels for juvenile chinook salmon (Onchorhynchus tshawytscha) in the Sacramento River. The system is particularly well-suited to a comparative study because young salmon migrating down the lower Sacramento River (Figure 1) in high flow years have two alternative paths: they may continue down the heavily-channelized main river or they may pass through the Yolo Bypass, the primary floodplain of the estuary. The 24,000 ha floodplain seasonally floods in winter and spring in about 60 percent of water years, when it is designed to convey up to 14,000 m3/s. Under typical flood events, water spills into Yolo Bypass via Fremont Weir (Figure 2) when Sacramento basin flows surpass approximately 2,000 m3/s.

We had several reasons to believe that floodplain habitat might be important habitat for young salmon. First, high flow years are known to enhance populations of a variety of estuarine species (Jassby and others 1995) and survival of young chinook salmon (Kjelsen and others 1982; Brandes and McLain forthcoming). However, the exact mechanisms for high flow years enhance populations of salmon and other species have not been established. Floodplain inundation is one of the unique characteristics of wet years, when the Yolo Bypass is likely to be a significant migration corridor for young Sacramento Valley salmon. During high flow events the Yolo Bypass can convey 75 percent or more of the total flow from the Sacramento River basin, the major producer of salmon in the system. Second, we had evidence that floodplain inundation provides major habitat for another migratory estuarine fish, the Sacramento splittail (Pogonichthys macrolepidotus) (Sommer and others 1997).

1. Location of Yolo Bypass in relation to the San Francisco Estuary and its tributaries

Materials and Methods

During 1998 and 1999 we studied the Yolo Bypass and the adjacent Sacramento River. Flow data were taken from U.S. Geological Survey gauges. Daily water temperatures for each site were calculated for single stations in the Sacramento River (USGS) and a data logger (Onset Corp) installed at the base of the Yolo Bypass (Figure 2).

1. Sacramento River, Yolo Bypass, and its primary tributaries. Sampling locations are shown for beach seine (circles) and water temperature (triangles).

Salmon fork length (mm) was measured from January through April in 1998 and 1999 from fish samples collected by 15-m beach seines. When the bypass was flooded, samples were collected weekly at five core locations (Figure 2) located around its perimeter. As the bypass was draining, additional samples were collected at semi-randomly selected ponds near the five core locations. Comparative data on salmon size in the adjacent reach of the Sacramento River were collected by USFWS at six stations using techniques similar to those used in the bypass. Additional information on salmon growth was collected using paired releases of coded-wire-tagged (CWT) salmon fry in the Yolo Bypass and Sacramento River. This approach allowed growth comparisons on fish of a similar origin and provided a relative estimate of migration time and survival. The salmon fry were produced and tagged at the Feather River Fish Hatchery and released on March 2, 1998 and February 11, 1999. The release sites were in Yolo Bypass below Fremont Weir (52,000 in 1998; 105,000 in 1999) and in the adjacent reach of the Sacramento River (53,000 in 1998; 105,000 in 1999). Each release group had a mean fork length of approximately 57 mm. Migration time and lengths of CWT salmon released in the Sacramento River and the Yolo Bypass were compared for fish recaptured at Chipps Island in the USFWS midwater trawl sampling program. Survival indices of the paired CWT releases were calculated by dividing the number of fish recovered at Chipps Island from each tag code by the number released, corrected for the fraction of time and channel width sampled.

We performed diet comparisons on fall-run size juvenile salmon collected in beach seine samples. The stomachs were removed from fish and the contents were identified with a dissecting microscope. Up to ten individuals of each prey type encountered were measured and assigned a dry weight using regression equations from the literature. Feeding success was examined in two ways: (1) prey biomass estimates from the stomach content analysis; or (2) prey biomass estimates as a function of maximum theoretical consumption. For the first measure, we used the stomach content data to calculate total prey biomass for individual fish. A limitation of using prey biomass as a measure of feeding success between locations is that thermal history affects how consumption alters growth rate. As will be discussed in further detail, water temperatures were significantly higher in the Yolo Bypass floodplain than in the Sacramento River. To correct this problem, our second approach used bioenergetic modeling to incorporate the metabolic effects of water temperature. We used methods similar to Rand and Stewart (1998) to calculate a wet weight ration index, which uses prey biomass for each sampled individual as a proportion of the theoretical maximum daily consumption rate. The theoretical maximum daily consumption rate (Cmax) was modeled using Fish Bioenergetics 3.0 (Hanson and others 1997) using model parameters from Stewart and Ibarra (1991) and observed body size and water temperature at the time of collection in beach seine sampling. The model was run for individual fish to estimate the wet weight ration index, then the results were grouped and analyzed as for prey biomass.

Results and Discussion

The 1998 and 1999 results suggest chinook salmon that rear on the Yolo Bypass floodplain have higher growth rates than those that remain in the adjacent Sacramento River channels. Mean length increased faster in the Yolo Bypass during each study year (Figure 3) and CWT fish released in the Yolo Bypass were larger when they emigrated the Delta than those released in the Sacramento River (Table 1). It is possible that these observations are due to higher mortality rates of smaller individuals in the Yolo Bypass or of larger individuals in the Sacramento River, however we have no data or reasonable mechanisms to support this argument.

Apparent growth differences between the two areas are consistent with water temperature and stomach content results. We found that the Yolo Bypass floodplain had higher water temperatures (Figure 3) and young salmon ate significantly more prey (Figure 4) than in the Sacramento River. The wet weight ration indices calculated from bioenergetic modeling suggest increased prey availability in Yolo Bypass was sufficient to offset increased metabolic requirements from higher water temperatures (Figure 4). Higher water temperatures in the Yolo Bypass are expected as a result of the shallow depths on the broad floodplain. Increased feeding success in the Yolo Bypass is consistent with trends in prey availability. Although Yolo Bypass and Sacramento River had similar levels of zooplankton, Yolo Bypass had dramatically more dipteran prey in the drift and in the fish stomachs (DWR, unpublished data). Studies by Rondorf and others (1990) showed that zooplankton were the least-favored prey items in juvenile chinook salmon diets. The dominance of zooplankton in the diets of Sacramento River salmon therefore probably reflects relatively low availability of other more energetically valuable prey items such as dipterans.

1. Fish size versus physical conditions in the Yolo Bypass and Sacramento River during winter and spring of 1998 and 1999: (A) mean daily flow (m3/s or cms) in the Yolo Bypass (solid line) and Sacramento River (circles); (B) mean water temperature (°C) at Yolo Bypass (solid symbols) and Sacramento River (open symbols); (C) mean daily chinook salmon fork length for Yolo Bypass (solid symbols) and Sacramento River (open symbols) beach seine stations. For presentation purposes, only the daily mean fork lengths are shown; however, individual observations for February-March were used for statistical analyses. The regression slopes for log10-transformed Yolo Bypass and Sacramento River fork length data were significantly different (t-test, p < 0.001) in both years.