Pescadero Marsh Natural Preserve Salinity,
Tidewater Goby and Red-legged Frog Monitoring 1995-96

Jerry J. Smith
Dawn K. Reis

Department of Biological Sciences
San Jose State University
San Jose, CA 95192
June 25, 1997

A Report Prepared for the California Department of Parks and Recreation 3790-301-722(7)

INTRODUCTION

The Pescadero Marsh, a 320 acre coastal wetland, includes an estuary/seasonal lagoon at the
confluence of Pescadero and Butano creeks, fresh and brackish water marshes, brackish water
ponds, and riparian areas along the streams. Modifications to the marsh complex due to past
human land uses include restricted water flow, due to a levee system throughout the marsh, and
reduced tidal prism, due to both the levees and sedimentation from land uses in the upper
watershed. Although it no longer functions as it did 150 years ago, Pescadero Marsh supports a high
diversity of animal and plant life, and is a refuge for a number of sensitive species (Smith 1990;
Jennings and Hayes 1990). Federally endangered tidewater gobies (Eucyclogobius newberryi)
use the lagoon and marsh habitats. Federally threatened California red-legged frogs (Rana
aurora draytonii) and federally endangered San Francisco garter snakes (Ihamnophis sirtalis
tetrataenia) use the fresher portions of the complex. Low salinity habitat (less than 4 parts per
thousand (PPT)) is required for California red-legged frog egg survival (Jennings and Hayes
1990), and relatively low salinity habitat (less than 7.5 PPT) is required for larval survival
(Jennings, pers. comm.). Tidewater gobies tolerate fresh or saltwater habitats, but avoid
strongly tidal areas when the sandbar is open (Smith 1990). North Marsh and Butano Marsh,
partially leveed wetlands in the northern and southern portions of the lagoon/marsh complex
(Figure 1), provide extensive habitat for both California red-legged frog and for tidewater goby,
but the quality of that habitat depends upon the timing of sandbar formation, water surface
elevations, the amount of flooded marshland and upon water salinity.

Portions of the Pescadero Marsh Restoration Project were implemented in the summer and fall
of 1993. One modification involved removal of portions of the levees separating North, Middle
and East Butano marshes (near water quality stations D3 and D6, Figure 1); previously an
opening had been made in the levee separating the eastern end of East Butano Marsh from
Butano Creek. These modifications allow Butano Creek flood waters to flow through the Butano
Marshes. They also allow tidal water, or water impounded by a closed sandbar, to move much
more easily throughout the Butano Marsh complex.

The second major restoration effort involved modifying the northern portion of the marsh
complex. A small culvert through the levee separating North Marsh and North Pond from
Pescadero Creek was replaced with 6 large culverts and two small culverts (water sampling
station B). In addition, a:levee that formerly separated North Pond was removed (north of water
sampling site C2).

Finally, a low levee (designed for + 5.5 feet) was added to separate North
Marsh from the channel leading to North Pond. Two large, normally-closed, culverts were
installed in the low levee (between water sampling sites C3 and Fl and between Cl and El).
One result of these modifications was to restore tidal action to North Pond, and the channel
leading to it, when the 6 large culverts are open; the culverts were to be left open except for
brief periods immediately following sandbar closure. The second intended result to was to
isolate North Marsh as a fresh-water to mildly brackish-water habitat for red-legged frogs and
San Francisco garter snakes. North Marsh would also serve as a potential refuge for tidewater
goby in case yellowfin goby (Acanthogobius flavimanus) became established in the saltier
portions of the marsh complex. The only open connection between North Marsh and the
remainder of the lagoon/marsh complex was to be a permanently open 12 inch culvert at +4.5
feet extending through the levee between water sampling sites Band El.

This report describes the results of water level and salinity sampling in 1994, 1995 and 1996 and
sampling for adult and larval frogs and tidewater gobies in 1995 and 1996. The monitoring was
designed to evaluate the functioning of the estuary/marsh complex in response to the restoration
actions and to propose additional management actions to maintain water levels, salinities and
other habitat conditions suitable for red-legged frogs, San Francisco garter snakes and tidewater
gobies.

Recommendation 1
Low levee levee should be raised to +5.5 to 6.0 ft to
prevent spills of saline water over the levee to North Marsh. The surface
of the levee should be revegetated or otherwise protected against erosion
when overtopped. The raised levee will store more water in North Marsh and
delay drying of the marsh and will also allow the regular resumption of
tidal flow to North Pond (with culverts open at station B)

Recommendation 2
The large culverts at Station B and at north and south
ends of the lee should be regularly maintained so that they do not leak and
can be opened and closed as needed.

Recommendation 3
The 2 small culverts at Station B should be periodically
checked to see that they are not clogged. The slide gates on the small
culverts do not work. A slide gate should be installed and maintained on
the culvert from Sation B to E1, so that it might be occasionally closed to
regulate salinity or height of water in North Marsh.

Recommendation 4
Proposed future actions include the opening of the levees
at the upstream end of East Delta Marsh. This would increase flood flows
through the marsh and might freshen the marsh in winter and early spring.
However, the levee opening also might increase use of the marsh by
bullfrogs, which in 1996 appeared to approach the marsh from the downstream
opening (G2) from their apparent source upstream on Butano Creek. If the
levee opening is at a high enough elevation so that a portion of the flood
flows, but not late spring and summer flows, passed through the break fewer
bullfrogs might enter East Delta Marsh. The present inoperable tide gate at
I (3/23/2010) Kristine Atkinson – RE: Were any Smith an~ @D1997) r~~omm~ndations imelemented?
East Butano Marsh could be modified rather than moved. This might keep the
marsh wetter and fresher longer in summer, and improve red-legged frog
larval survival.

Recommendation 5
The Trout Ponds should be maintained as seasonal ponds
and not converted to permanent freshwater habitats by heavy diversion of
water from Pescadero Creek; permanent water would result in the
establishment of a reproducing bullfrog population.

Recommendation 6
The water right on Pescadero Creek could be used to
augment the water level of the Trout Ponds in spring and early summer of dry
years, so that red-legged frogs could metamorphose before the pond dried.
The diversion could also be used to augment and freshen the water in the
south ditch (E1-3) of North Marsh in dry years.

Recommendation 7
Continue to monitor water quality and tidewater goby and
red-legged frog populations, especially in years when the sandbar forms
early and conditions are different from those observed in 1995-96. Water
quality stations that should be monitored are: B, C1, or C3, C4, D3, 5, 6,
E1-3, F1-2, G1-2, H, an S1-2. Monitoring of larval or juvenile frogs is
probably most useful.

Recommendation 8
Movement of red-legged frogs and bullfrogs are not known,
but are apparently important to the biology of both species. Red-legged
frogs could be radio-tracked in late summer to see what habitats provide
refuges hen the marshes dry or become salty. Bullfrogs could be
radio-tracked to determine seasonal movements and potential sources within
the watershed.

Recommendation 9
San Francisco garter snake numbers and season movements
are unknown. They could be trapped with drift fences and funnel traps, PIT
tagged to identify individuals, and radio-tracked to determine movements and
habitat use.

Recommendation 10
If bullfrogs become abundant at Pescadero Marsh, a
management plan to reduce them may be needed. Possible management actions
might include periodically managing for salinity and water levels, like
those seen in 1995 and 1996, and attempts to reduce bullfrog populations at
major sources in the watershed.

Check out Part 1 of this report here in pdf format.

Check out Part 2 of this report here in pdf format.