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Interagency Ecological Studies Program for-the Sacramento-San Joaquin Estuary LIBRARY COPT - NEWSLEITER BAY-DELTA FISHERY PR~::~;1994 Readers are encouraged to submit brief articles or ideas for articles. Correspondence, including requests for changes in the mailing list, should be addressed to Randy Brown, California Department of Water Resources, 3251 S Street, Sacramento, CA 95816-7017. EDITOR'SNOTE:Thefollowing article was submitted by Dr. Bruce Herbold of the U.S.Environmental Protection Agency. The author describes the data and rationale he used to arrive at estuarine habitat standards to protect delta smelt. Written comments on this or other articles In the Newsletter are welcome and will be presented, along with the author's responses, in the spring edition. -R. Brown and P. Herrgesell Habitat Requirements of Delta Smelt Bruc,z Herbold, USEPA One of the greatest difficulties in question is: "Does the occurrence springs (Sweetnam and Stevens devising protection for the threat- and duration of suitable habitat 1993). ened delta smelt has been to deter- during the spawning and nursery When delta smelt are in Suisun mine exactly what is threatening period in spring relate to subse- Bay, they are found in greatest them. In their recent Biological quent delta smelt adult fall abun- abundance at stations in the shal- Assessment, DWR and USBR dance?" pointed out the lack ofa significant lows (Moyle et al 1992). It is un- relationship between delta smelt Delta smelt are found in greatest clear whether this greater capture abundance and a wide array of abundance at salinities near 2 ppt rate reflects a habitat preference of variables. The absence of a simple (3.0 mS/cm). During the recent smelt or greater efficiency of the linear relationship with any of the drought almost the entire popula- sampling gear. environmental factors associated tion was found near Emmaton (Figure 1), where bottom salinity with flow results from delta smelt's Methods apparent low abundance in years stayed near 2 ppt almost year- of either very low or very high flow round. By contrast, in 1993 about The quantity of shallow, low- half the population remained in conditions (Moyleet al1992; Moyle salinity habitat available each year and Herbold 1989.) The following Suisun Bay throughout the sum- was estimated by calculating the analysis focuses on the habitat re- mer, although the region of 2 ppt number ofdays between February 1 quirements ofyoung delta smelt as retreated upstream. This is consis- and June 30 when salinities of2 ppt low salinity water in or near shal- tent with the pattern in' earlier were in Suisun Bay. The numbers low habitat (Moyle et al1992). The years when dispersal of delta of days were calculated based on smelt was greater fO'llowingwetter the fall is significant at the 0.05 level (r=0.496). Figure 2 is a scatter plot of the data, with each point labeled by year. The driest year on record (1977) and the wettest year on re- cord (1983) both provided no days of2 ppt in Suisun Bay and resulted in low abundances of delta smelt. 'Ibtal delta outflows were similar in 1986 and 1993, but the single large storm in 1986 did not provide as much habitat, or as many delta smelt, as the more prolonged pre- cipitation of 1993. The early 19708 yielded successive years ofvery high delta smelt abundance despite pro- ducing as few as 60 days of2 ppt in Suisun Bay. 'Ib identify which areas in Suisun Bay contributed mostto the overall relationship, I calculated a sepa- rate correlation for each 5-lan reach of the delta smelt historical range (San Pablo Bay to Rio Vista). The number of days when 2 ppt was in FlQUre 1 each 5-km reach was correlated SACRAMENTO-SAN JOAQUIN DELTA with the subsequent abundance of delta smelt. The resulting Pearson outflow (QOUT from the DAY- Results and Discussion correlation coefficients are shown FLOW data set) and the X2 equa- in Figure 3, labeled by a shore tion described in Kimmerer and The correlation between the num- location near the upstream end of Monismith (1993); ie, ber of days from February through each reach. The correlation for the June when mean daily salinities of X2t=10.16+0.945·X2~.1t1.48rLog,o(00UT}t reach from Roe Island to Middle 2 ppt were in Suisun Bay and the Ground is significant at the 0.01 These calculated values have been abundance of adult delta smelt in level. It is the only signific;:ant shown to accurately reflect meas- ured salinities in and near Suisun Bay (Kimmerer and Monismith 2000 T I a. 1993). The calculated values pro- u 70. .80 vide a continuous data set, unlike Cca '0 the salinity data, which contain c 1500 :::J many gaps and do not include data ,Q 0« 72. for all stations in all years. For 73• •• 1993, a preliminary estimate ofthe "i 1000 Delta Outflow Index was obtained E rn from DWR. Springtime conditions CD 81. .8a in each year from 1967 to 1993 •• "i ~7 were compared with subsequent Q 500 87. a8 .•2. • a1 abundance of delta smelt as meas- - '8 88. 87 • 'i • a8 I&. 82. .84 ured by DFG's fall midwater trawl '.a aa. survey (excluding 1974 and 1979, 0 I I which were not sampled). Data used 0 50 100 in this analysis are available from the author. Number of Feb-Jun Days with 2 ppt In Suisun Bay FIQure2 SPRING HABITAT EFFECTS ON DELTA SMELT RECRUITMENT value (:r=0.558).Note that all values ~ downstream of Carquinez Bridge c CD or upstream of Chipps Island are U .•.;: negative, while all sites in Suisun CD o Bay are positive. o c Th try to pinpoint the months of o ;: greatest sensitivity in this relation- III ship, I calculated a separate corre- 'i.. o.. lation for each month of the year. o The number of days when 2 ppt c was in Suisun Bay for each month ..~ -0.2 ofthe water year preceding the fall III CD midwater trawl was correlated a. with the subsequent abundance of "0:'\OO\.~,,\t't'S\lE.,,C~i\~"~••10~,~\\..E.'oI\S1" delta smelt. The Pearson correla- ••• co"f'o,; s.,... E.~ ,,\0 tion coefficients for each month are FIgUre 3 displayed in Figure 4. Correlations CORRELATIONS WITH 5-KM REACHES from October through May are high but only the peak in April ••c represents significance at the 0.05 CD level (:r=0.486). U 0.4 .•.;: However, within a year, the auto- CD o 0.3 correlations in time and space re- o duce the reliability of any analysis ~ 0.2 that compares parts of years or ;; II small geographic areas. ! 0.1 o.. o 0.0 Conclusions c o The resurgence of delta smelt in f! -0.1 II CD 1993 to the highest abundance in Q. 13 years, after a 12-year period of record low abundance, suggests stock/recruitment relationships FIQure4 play a small role in determining CORRELA nONS IN EACH MONTH the fall abundance of delta smelt. The higher captures of delta smelt ability of suitable habitat limits However, spring of 1993 provided near waters of2 ppt and in shallow the abundance of this species. In more of the habitat this species habitats (when waters of2 ppt are the absence of a significant stock! appears to require than any other near shallow habitats) strongly recruitment relationship or tie to year on record. The recent high suggest habitat selection·by delta any other environmental variable, abundance of delta smelt is consis- smelt. The tie between the amount availability ofnursery habitat seems tent with the pattern in earlier of this habitat and fall abundance to be the primary limiting factor to years when springtime conditions of delta smelt argues that avail- abundance of adult delta smelt. in Suisun Bay correlate well with fall abundance. References There is some evidence that a large Kimmerer, W, and S Monismith. 1993. An estimate of the historical position of 2 ppt part of this relationship rests on salinity in the San Francisco Bay Estuary. in Managing Freshwater Discharge to the San Francisco Bay/Sacramento-San Joaquin Delta Estuary: The Scientific the number of days in April when Basis for an Estuarine Standard. San Francisco Estuary Project. salinities of 2 ppt are between Moyle, PB, B Herbold, DE Stevens, LW Miller. 1992. Life history and status of the delta Middle Ground and Roe Island. smelt, Hypornesustranspacificus, in the Sacramento-San Joaquin Estuary, Califor- However, for 1993, larval smelt nia. Trans Am Fish Soc 121:67-77. were reported as early as February Moyle, PB, and B Herbold. 1989. Status of the Delta Smelt, H:Jl1X21lKSUS transpacificus. and as late as June, so nursery Final Report to US Fish and Wildlife Service. 19 pp + app. habitat may be needed throughout Sweetnam, DA, and DE Stevens. 1993. Report to the Fish and Game Commission: A the 5-month period. Status RelJiewof Delta SmeU (lbpomesus transpacificus) in California. Candidate Species Status Report 93-DS. Potamocorbula Amurensis Survey Peggy Lehman, DWR, and Wayne Fields, Hydrozoology Introduction of the Asian clam Po- data were based on natural geog- where densities reached only 9,578 tamocorbula amurensis (Mollusca raphy. Hymanson (1991) described clamslm2. Densities near 9,578 Corbulidae) in the San Francisco the methods in detail. clamslm2 were also measured in Bay/Delta estuary in 1986 has Suisun Marsh. In Suisun Bay, den- been of great concern because of its sities were comparatively low; high grazing rate (Hollibaugh and maximum density for a single sta- Werner 1991) and an associated Distribution of P. amurensis was tion was 4,981 clamslm2 in Grizzly decrease in cWorophyll biomass similar during 1990 and 1993.