During this sampling period a total of 15 Chinook were caught which brings the season total to 19 Chinook. The largest daily catch of Chinook was three fish which occurred on both April 3^rd and April 13^th. Individual fork lengths ranged from 62 mm to 92 mm. Mean length for Chinook captured during this sampling period was 79 mm and mean weight was 6.1 grams (Figure 1).

Figure 1. Photo of a Chinook salmon parr caught on 4/20/07. [click on the photo for enlarged view]

The California Department of Fish and Game (CDFG) will be releasing a total of 300,000 coded wire tagged (CWT) Chinook between April 20^th and May 8^th into the Merced River. The first release of 100,000 CWT Chinook occurred on April 20^th from the Merced River Hatchery (RM 52). This is the first of six scheduled releases of CWT Chinook on the Merced River. In the upcoming weeks we expect more wild Chinook in our trap as a result of increased flows associated with the Vernalis Adaptive Management Program (VAMP)(Figure2).

Figure 2. Preliminary VAMP flow increase schedule for the Merced River. [click on the chart to download VAMP schedule]

Flow increases for VAMP began on April 19^th and will rise gradually until they peak at ~950 cfs on May 9^th.   Higher flows have lead to an increase in fish catch, in addition to more debris entering the trap requiring and increased monitoring effort (Figure 3).

Figure 3. Photo of a FWS employee Paul Miklos processing live box of the south trap at Hatfield State Park on April 10, 2007. [click on the photo for enlarged view]

No efficiency tests were conducted during this sampling period, however, CDFG has authorized the use of hatchery fish for tests starting later this month.

During this sampling period a total of eight different types of incidental species were captured including white catfish, bluegill sunfish, prickly sculpin, western mosquitofish, Sacramento sucker, smallmouth bass, spotted bass and largemouth bass (Figure 3).

    

Figure 4. Photo of a white catfish captured on April 13 (left) and two spotted bass captured on April 16 (right). [click on the photo for enlarged view]

Environmental Data: 

Instantaneous water temperature measured at the Hatfield rotary screw trap ranged from 58.5°F to 66.6°F.  Instantaneous turbidity measured at Hatfield rotary screw trap ranged from 0.81 to 6.13 NTU.  During the sampling period flows at Snelling (MSN; RM 46) ranged from 263 to 474 cfs, and at Cressy (CRS; RM 27) from 176 to 374 cfs.  Hourly flows in Dry Creek (DSN; confluence at RM 31.5), which is a significant tributary to the Merced River, ranged from 25 to 67 cfs.