Minnow Trapping
Collection of the longjaw mudsucker was accomplished using baited minnow traps in first-order channels (creeks) of mature pickleweed marsh and along fringes of ponded water inside breached ponds. The study began in July 2010, with pilot sampling taking place approximately bi-monthly (July, August, October, November, and December) at several sites to determine optimal locations for long-term study sites. We chose reference sites with remnant pickleweed marsh on the outside levees of restored ponds, where at least 3 traps could be spaced evenly at approximately 5 meters apart along creek habitats to represent the source population for fish emigrating into restored ponds. This was not possible for many sites as very few remnant marsh creeks remaining or were overgrown with cordgrass (Spartina) or tules (Schoenoplectus) (e.g., outside ponds A8, A19, A20, and A21). We searched restored ponds for creek habitat and only pond A21 had pickleweed on the marsh plain where creek habitat was beginning to form; therefore, we selected fringing pickleweed along the borrow-ditch edges as test sites for most pond sites. Several sites were only sampled once or infrequently during the pilot period due to no catch or difficulty of access.
Study Design
We selected 3-5 replicate creek habitats per site. Each site was sampled with 1-5 baited minnow traps (depending on creek length) for a minimum of 12 hours overnight during the full-moon spring tide, when the highest monthly tides occur. Monthly sampling began in May 2011 and has been ongoing at ponds A6, A8, and A21 in the Alviso Marsh Complex and at SF2 at Ravenswood (Figure 2). Quarterly sampling has been occurring at the outer Bair island restored pond and Pond E9 at the Eden Landing Complex because of overall low catch. All fish species collected were counted and measured for standard length, and all invertebrate taxa were identified to species and enumerated. A sub-sample of Longjaw Mudsucker, Pacific Staghorn Sculpin, Three-spine Stickleback and Yellowfin Goby were wet-weighed for assessment of fish condition.
Alviso Marsh Complex
Pond A6 (A6_I, A6_O) is a fully tidal pond with two breaches along Alviso Slough that were opened in November 2010. We chose 4 reference creeks along the remnant marsh outside the second northernmost breach to the pond. Initially, our first creek occurred where the breach occurred and we were forced to abandon this location. This area is characteristic of a remnant marsh that was altered by pond formation, with a levee built at the uppermost edge. Creek habitats are relatively intact, with short meandering reaches creating steep undercut banks that provide habitat for the longjaw mudsucker. Creeks are 30-40 meters in length and average a depth of 1.5 meters. The marsh plain is dominated by pickleweed and very little cordgrass occurs on the marsh plain. Inside A6, the margins of the borrow ditch are forming pickleweed marsh; however, creek formation has not yet occurred.
Pond A8 (A8_I) is a tidally muted pond, with the water levels dictated by flood-control plans. Depths are usually between 1-3 meters. The pond is surrounded by hardened rip-rap levees with very little pickleweed marsh. One small patch of pickleweed occurs at the old boat launch just north of the tide gates; however, this area is dewatered approximately half the year due to fluctuating water levels, rendering this location as a long-term study site difficult. We chose three lines (~30m length) along the southeast levee along the road, and when inundated we sampled the pickleweed marsh adjacent to the boat launch east levee. In May 2012, we began sampling just outside the tide gate along the edge to monitor for recruitment of juvenile longjaw mudsucker.
Pond A21 (A21_I, A21_O) was the most extensively surveyed since it has the largest marsh plain, with pickleweed filling in much of the open space and pockets of cordgrass occurring as well. We have sampled extensively along the borrow ditch edges (east, west, and north levees), along the inside of the large slough forming within the middle of the marsh, and along the marsh plain along the northeastern edge. Here we identified four reference creeks of about 60-meters length with pickleweed beginning to line the banks. We began consistently sampling these locations in May 2012. Sites within the interior of the marsh plain did provide catches of longjaw mudsucker; however, access to this area has been very limited and navigation has been dangerous, thus we decided not to continue sampling in this area. We selected five creeks outside the northern levee along Mud Slough as our outside remnant pickleweed marsh site. The creeks here are only about 10 meters in length and less than one meter in width. During the survey, the banks began collapsing and have required continued maintenance.
Ponds A19 and A20 were sampled extensively in the first year of the study, with catches being sporadic but at times relatively high in the summer, averaging 1-3 per trap, when juveniles were searching intertidal habitat. In both ponds no pickleweed marsh has begun to grow on the marsh plain and only a very narrow fringing marsh exists. Since very little habitat existed in these ponds, we decided to abandon A19 and A20 to focus more effort in A21.
Ravenswood
We chose three reference creeks along the outside of Pond SF2 (SF2_I, SF2_O), which average 30-60 meters in lengths and are less than one meter in depth. One of the three creeks is less than 0.3 meters in depth and is only inundated on the highest spring tides of the month. The first creek (nearest the road) is a long meandering creek that is bifurcated into two first-order creeks and, as a result, is given twice the trap effort as the other two creeks. Inside SF2 along the east edge of the levee and the walking path, we chose 3 lines of about 30 meters in length, one before the breach and two after the breach.
Outer Bair Island (OB_I, OB_O). We extensively sampled outer-outer Bair Island (north side of Corkscrew Slough) and the outer Bair Island restoration pond beginning July 2010, with very few sites producing longjaw mudsucker. It was not until June 2012 that we settled on one creek site outside of the easternmost breach where a small patch of picklweed marsh exists. We also sampled inside the pond along the borrow-ditch edge and the marsh plain where pickleweed has been recruiting significantly in the last year.
Eden Landing (WT1-3, E9_I, E9_O, E8A, E8X). We sampled many pilot sites at the Eden Landing complex prior to breaching of E9, E8A, and E8X. Initial sampling occurred in July 2010 when restoration ponds were drawn down for construction. We sampled the remaining ditch waters adjacent to culverts and collected many longjaw mudsuckers; however, these sites were destroyed in the construction process. Two short creeks (~10m ) along the Whales Tail Marsh (WT1) on the northwest corner outside the E9 breach were chosen as long-term sites. These sites have mature pickleweed marsh but are littered with trash from the bay. South of WT1 within the Whales Tail Marsh, we selected a second creek site with mature marsh and meandering channels. We have yet to establish consistent trapping sites inside the restored pond, but in June 2012 we successfully collected longjaw mudsucker from the northeast corner where water flows into E13 from E9. This will likely be our long-term inside pond site for Eden Landing.
