ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

Home Browse Search

found in the Bay-Delta estuary where salinity is generally less than 2 parts per thousand(ppt). Except when spawning in fresh water, delta smelt are most frequently documented in, or slightly upstream of,the entrapment zone,where riverine freshwater flow in the estuary mixes with seawater and the salinity is between 0.5 ppt and 5.2 ppt(SWRCB and USACE 1995). Since the early 1980s, delta smelt have been most abundant in the northwestern Delta in the Sacramento River(USFWS 1994,Bennett 2005). Delta smelt disperse widely into fresh water in late fall and winter as the spawning period approaches, and may move as far upstream as Mossdale on the San Joaquin River(SWRCB and USACE 1995). However, in most years, delta smelt spawn primarily in the upper end of Suisun Bay,in Montezuma Slough, and in the southern and central Delta. They spawn in shallow, fresh or slightly brackish water upstream of the mixing zone. Most spawning happens in tidally influenced backwater sloughs and channel edgewaters (Moyle 2002;USFWS 2004). Larvae hatch between 10-14 days, are planktonic(float with the water currents), and are washed downstream until they reach areas near the entrapment zone where salt and fresh water mix. Delta smelt are fast growing and short-lived with the majority of growth within the first 7 to 9 months of life. Most smelt die after spawning in the early spring although a few survive to a second year. Delta smelt feed entirely on small crustaceans called zooplankton(Moyle 2002;USWFS 2004). Swanson and Cech(1995)conducted a series of laboratory investigations to identify the critical thermal maximum temperature threshold for delta smelt. Results of these laboratory investigations demonstrated that the upper thermal threshold for delta smelt is approximately 13-167 (delta T)above ambient with a maximum temperature of 77°F. Delta smelt abundance fluctuates greatly from year to year,however,recent information has demonstrated a dramatic decline of the delta smelt population(Bennett 2005). Their short lives and relatively low fecundity make populations susceptible to reduction following periods when conditions are unfavorable, such as during droughts. The declines have been attributed to reductions in Delta outflow in some years, excessively high outflow in other years, entrainment losses to water diversions, changes in food organisms,toxic substances, loss of genetic integrity, and habitat destruction(particularly loss of shallow-water habitat) (Moyle et al. 1995;USFWS 2004). Based on available information,the following temperature guidelines have been identified for delta smelt: ► Optimal range: 44°F to 60°F ► Range of increasing adverse effects: 617 to 68°F ► Lethal effects: >77°F; delta T of 13°F to 16°F Sacramento Splittail On September 22,2003 the USFWS removed Sacramento splittail from the list of threatened species. The USFWS determined that threats to Sacramento splittail are being addressed through habitat restoration actions such as the CALFED Bay-Delta Program and the Central Valley Project Improvement Act(CVPIA); as a result, splittail are not likely to become endangered in the foreseeable future. Sacramento splittail are endemic to California. Except for very wet years,they are mostly confined to the Delta, Suisun Bay, Suisun Marsh, and Napa Marsh(USFWS 1999). In recent years, splittail distribution appears to have been concentrated in the lower Sacramento River and south Delta(SWRCB and USACE 1995). Overall,the species distribution has been reduced to less than one-third of its original range. Splittail are typically found in waters with temperatures between 41°F and 75°F,but individuals acclimated to high temperatures can survive rapid changes and temperatures of 84°F to 91°F for short periods. They can also survive low dissolved oxygen levels(<1 milligram oxygen/liter [mg/1]). These tolerances make splittail well- suited to slow-moving sections of rivers and sloughs(Moyle 2002). Manteca WQCF and Collection System Master Plans EIR EDAW City of Manteca 4.13-9 Fisheries and Aquatic Resources