An evaluation of rehabilitation efforts based on carcass recovery and spawning activity

Spawning surveys were conducted for three years in Mendocino County streams. The results from the last two years of surveys are reported here. Surveys were conducted in seven watersheds in 1991 1992 and in ten watersheds in 1990-1991. These surveys were conducted to as a means to evaluate the effectiveness of restoration efforts to restore salmon populations. The populations of chinook and coho salmon were estimated by several methods including marking and recapture of carcasses, area-under-the-curve (AUC) method and from numbers of redds. A new model was developed to estimate spawning numbers which incorporated estimates of the average daily retention rate of carcasses. The reliability, of estimates are assessed in two streams where known numbers of fish were released. In both areas carcass retention and AUC estimates produced numbers_ far less than the of fish released. Redd counts were used to establish a range in spawning estimates which are believed to encompass the actual populations. It was determined that coho salmon could be expected to produce between 1 and 4 redds per female and chinook salmon from 1 to 1.8 redds per female.

The largest population of coho salmon was found in the South Fork Noyo where the run is enhanced through artificial production. This run ranged between 681 and 1197 in 1991-1992 and between 208 and 400 in 1990-91. The remainder of coho runs surveyed were supported by natural production only. The Hollowtree Creek coho run was about 120 fish in 1991-92 and between 50 and 90 in 1990-91. Caspar Creek had between 50 and 200 in 1991-1992 and between 8and 28 in 1990-1991. Little River had less than 30 in 1991-1992 and only a single pair in 1990-1991. The Pudding Creek coho run was_ between 20 and 100 fish both years. The chinook run in Hollowtree Creek was between 270 and 420 in 1991-92 and between 18 and 53 in 1990-91. The 1991-92 chinook run was composed of 5, 5, 51, 35 and 3 percent age 2, 3, 4, 5 and 6 year old fish, respectively. Returns from hatchery released chinook composed 10 percent of the age four fish. In some areas, low water conditions are believed to have impacted the number of fish that spawned.

Of five streams into which coho were reintroduced, only one had spawning activity believed to be returning coho adults from plantings. The number in this stream was quite low- only two to eight spawning coho. It is believed that low flows conditions may have prevented coho from entering planted streams. Introductions of chinook salmon into the Ten Mile River have resulted in natural chinook production. Habitat restoration activities could not be linked to improved coho or chinook salmon production in Mendocino County streams.