EPA's Vessel General Permit and Small Vessel General

Francisco, San Pablo, and Suisun Bays eastward to Chipps Island at the confluence of the
Sacramento and San Joaquin Rivers. Tributary streams to Suisun Marsh including Suisun Creek,
Green Valley Creek, and an unnamed tributary to Cordelia Slough (commonly referred to as Red
Top Creek), excluding the Sacramento-San Joaquin River Basin, as well as two artificial
propagation programs: the Don Clausen Fish Hatchery, and Kingfisher Flat Hatchery/ Scott
Creek (Monterey Bay Salmon and Trout Project) steelhead hatchery programs.
The DPS is entirely composed of winter run fish, as are those DPSs to the south. As winter-run
fish, adults migrate upstream December-April, and smolts emigrate between March and May
(Shapovalov and Taft 1954, Hayes et al. 2008). At the time of the 1996 status review and 1997
listing, little information was available on the specific demographics and life history
characteristics of steelhead in this DPS. While age at smoltification typically ranges from 1 to 4
years, recent studies by Sogard and Williams (2009) indicate that growth rates in Soquel Creek
likely prevent juveniles from undergoing smoltification until age 2. Survival in freshwater
reaches tends to be higher in summer and lower from winter through spring for year classes 0
and 1 (Sogard et al. 2009). Larger individuals also survive more readily than do smaller fish
within year classes (Sogard et al. 2009). Greater movement of juveniles in fresh water has been
observed in winter and spring versus summer and fall time periods, with smaller individuals
more likely to move between stream areas (Sogard et al. 2009). Growth rates during this time
have rarely been observed to exceed 0.3 mm per day and are highest in winter through spring,
potentially due to higher water flow rates and greater food availability (Boughton et al. 2007,
Hayes et al. 2008, Sogard et al. 2009).
Status and Trends
The Central California Coast steelhead DPS was listed as a threatened species on August 18,
1997 (62 FR 43937); threatened status was reaffirmed on January 5, 2006 (71 FR 834).
Estimates of historical abundance are provided here only for background, as the accuracy of the
estimates is unclear. An estimate of historical abundance for the total DPS is provided by CDFG
at 94,000 fish. This estimate is based on a partial data set and “best professional judgment” (see
Good et al. 2005). Other estimates of historical abundance are on a per river basis: Shapovalov
and Taft (1954) (as cited in Busby et al. 1996) described an average of about 500 adults in
Waddell Creek (Santa Cruz County) for the 1930s and early 1940s.
No current estimates of total population size are available for this DPS, and consequently there is
no time series data available to evaluate the central California coast steelhead population trends.
Rather, a general dearth of data on adult steelhead within the DPS, led the biological review team
to examine data collected on juvenile steelhead (see Good et al. 2005). In general, juvenile data
is considered a poor indicator of the reproductive portion of the population as juvenile age
classes exhibit greater mortality rates, which are closely tied to stochastic events, and may move
widely within a basin (which may include intermixing with other populations). There is no
simple relationship between juvenile and adult numbers (Shea and Mangel 2001). Nonetheless,
there was not enough adult data upon which the biological review team could base an assessment
of the population trends within the DPS. Therefore, the biological review team log-transformed
and normalized juvenile survey data from a number of watersheds (presumed populations). As a
result, the team derived trend estimates for five populations: the San Lorenzo River, Scott
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