Scientific Investigations Report 2006–5225
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5225
We used the terms embryo, free embryo, and larva to describe white sturgeon early life stages detected during sampling. These terms are adapted from Balon (1975, 1984).
The term embryo is used to define the life period that begins at fertilization and ends at hatch. White sturgeon embryos gain nutrition endogenously. The free embryo period begins when an embryo hatches from its egg casing. At this stage sturgeon still receive all nutrition endogenously from a yolk sac. This period ends with the transition to exogenous feeding. The larval period for sturgeon begins with the start of exogenous feeding and ends when fins and organs are fully formed.
Eight types of collection gear were used to sample for embryos, free embryos, and larvae (table 1). Two gears, artificial substrates and plankton nets, are commonly used to collect early life stages of white sturgeon. In addition to these gears we used kick nets, suction devices, and a view scope to search for embryos, free embryos, and larvae among rock crevices and in vegetation where artificial substrates and plankton nets have not been used.
Collection efforts were made in various areas including the main channel of the Columbia River, the shallows on the main channel side of the islands, the shallows along the Oregon shore, and the side channel that runs between the islands and the Washington shore. The federal navigation channel was not sampled due to a high volume of commercial and recreational boat traffic. Figure 2 shows an overview of areas sampled.
Artificial substrates based on McCabe and Beckman (1990) were deployed and retrieved from a 4.9-m aluminum johnboat. Individual 76 × 91-cm artificial substrates were placed on the river bottom parallel to the river current. Each artificial substrate was set individually with one claw anchor and a set of surface floats. A Global Positioning System (ETrex Legend®, Garmin International, Inc., Olathe, Kans.) waypoint was taken for the location of each artificial substrate. The water depth at the time of deployment was recorded for each substrate using the boat’s depth sounder. After retrieval, artificial substrates were inspected visually and any embryos present were removed using forceps.
A 25 × 46-cm rectangular frame kick net (Watermark bottom aquatic kick net, Forestry Suppliers, Inc., Jackson, Miss.) with 500-micron mesh was used to sample for embryos, free embryos, and larvae in wadeable water. Kick net sampling was done by placing the long axis of the frame of the kick net on the substrate perpendicular to the river bottom. The substrate would then be disturbed directly upstream from the kick net (fig. 3). The nets also were repeatedly swept through inundated vegetation.
Plankton nets were used extensively during this study. Plankton nets were mounted in three configurations to sample both wadeable and non-wadeable water. Plankton nets were mounted on two differently shaped frames, D-shaped and square. The D-shaped net was fished with the flat side of the ‘D’ in contact with the river bottom. It measured 75 cm at its widest point and a maximum of 53 cm in height. The D-shaped plankton net was constructed of 2-mm knotless mesh. The square plankton net had a 50 × 50-cm frame with 500-micron mesh.
Wadeable water was sampled using D-shaped and square-framed plankton nets. The nets were staked into the substrate so the bottom of the frame was in contact with the substrate and the frame was perpendicular to the river bottom. Plankton nets were fished for variable time increments. Once staked into the substrate, plankton nets were visually monitored to assure they were fishing properly. After about 30 minutes of sampling, the collection cup of the plankton net was removed and the contents were poured into a 0.95-L glass jar. The collection cup was then reattached and the net was redeployed to continue sampling. The contents of the jar were visually inspected for the presence of white sturgeon embryos, free embryos, and larvae.
Non-wadeable water was sampled with D-shaped plankton nets. Two D-shaped plankton nets were simultaneously deployed from a 7.6-m aluminum boat anchored in the current. Each plankton net was weighted with two 9-kg lead balls on the bottom of the frame to facilitate the net reaching the substrate and being held in an upright position in the strong currents. The plankton nets were retrieved and checked after each one-half hour of sampling. The collection cup of the plankton net was removed and the sample was visually inspected for embryos, free embryos, and larvae.
Three gears were used less than one hour each and were minor components of the study. A manual bilge pump (Thirsty-mate® Hand Pump; West Marine, Watsonville, Calif.) was used to suction the interstitial spaces of the substrate. A slurp gun (Rick’s Tackle, Long Beach, Calif.) was used in a similar manner as the bilge pump. A view scope (Aqua Scope II™; Lawrence Enterprises, Seal Harbor, Maine ) was used to observe submerged vegetation for attached embryos.
Due to the various gears used, effort was measured in hours. The measurement of effort in hours acted as an estimation of effort and a relative comparison of use among gears, but was not an attempt to compare the effectiveness of gears or quantify the amount of habitat sampled.
Data pertaining to river environment were collected from multiple sources. Elevation and flow data for Bonneville tailrace and Ives Island were taken from the Fish Passage Center website (Fish Passage Center, 2005). Temperature data for Ives Island was also obtained from the Fish Passage Center website (Fish Passage Center, 2005). The gage recording the Ives Island data was near the upriver terminus of the channel on the north side of Ives Island. Temperature data for the Bonneville tailrace were from the Columbia River Data Access in Real Time website (Columbia River Data Access in Real Time, 2005). Bonneville tailrace data were collected by a water-quality monitoring station near Cascade Island directly on the downstream side of the Bonneville Dam.
River environment data were collected during field sampling of all free embryo and larva capture sites. Depth was recorded using a top set wading rod (Swoffer Instruments, Inc., Seattle, Wash.). Temperature data were collected using a YSI handheld water-quality meter (Model 85D, YSI, Inc., Yellow Springs, Ohio) Velocity measurements were made with a Swoffer direct reading current velocity meter (Model 2200, Swoffer Instruments, Inc., Seattle, Wash.) attached to a Price AA bucket wheel. Six velocity readings were taken over a one-minute period and then averaged to obtain a composite velocity for each capture site.
Embryos, free embryos, and larvae captured during field sampling were immediately placed in sample vials containing 95 percent ethanol. After about one month, the alcohol was removed from the samples and replaced with a 10 percent solution of formalin. After a minimum one-month fixation in formalin the samples were drained and then filled with 70 percent ethanol. During the process of switching mediums of preservation, the sample vials were filled with distilled water for 10 minutes and then drained to remove any latent residues.
Embryos, free embryos, and larvae were inspected using a dissecting microscope. Each embryo was assigned a numbered stage of development based on Beer (1981). Free embryos and larvae were assigned a stage of development in days post-hatch based on Beer (1981).
During August 2005, riverbed substrates were characterized at sites where embryos, free embryos, and larvae were collected. Grid counts (Bunte and Abt, 2001) were used to sample surface substrates for characterization. A 120 × 120-cm portable sampling frame was used to randomly select substrate particles for measurement. Substrate particles that were directly underneath each intersection of the grid were measured using a gravelometer. The grid spacing of the sampling frame was 13.2 cm. The sampling frame grid contained 64 intersections (fig. 4).
A Global Positioning System receiver was used to navigate to the sites in which early life stages were captured during the June sampling period. At each site the portable sampling frame was laid upon the substrate. At each site, 128–137 (mean = 130) substrate particles were measured, therefore, the sampling frame had to be placed a minimum of twice at each site. When a particle was large enough to be contacted by two intersections of the sampling grid it was measured only once. In this case, the sampling frame would be laid down a third time to make up for particles that could be measured only once because they were touched by two grids. When it was necessary to lay the sampling frame down a third time, a random number from 1 to 8 was chosen along with a random side from which to start the measurements. This random number combination would determine from which transect of the grid the particles would be measured.
A US SAH-97 hand-held particle size analyzer (commonly known as a gravelometer) was used to measure the b-axis of each particle. The US SAH-97 has 14 square holes that range from 2 to 180 mm. Particles greater than 180 mm were measured with a ruler built into the side of the gravelometer. Each substrate particle measured was put into one of 16 size classes. The smallest classification for a particle-size class is fines (< 2 mm) and the largest is boulder (≥ 256 mm). Each particle was measured individually based on which hole it could fit through in the gravelometer. Particles were tallied to create a size class percentage frequency of each sample. A complete guide for using the US SAH‑97 particle-size analyzer is outlined in Potyondy and Bunte (2002).
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Department of the Interior | U.S. Geological
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