Horse Linto and Willow Creek Downstream Migrant Trap Results and Following Adult Returns 1995-1998 

Drawn from: Dutra, B.L. and S.A. Thomas. 1999. 1998-99 chinook and coho spawning report. Final: April 1999. USDA Forest Service, Six Rivers National Forest. Lower Trinity Ranger District. Willow Creek, CA. 18 pp.

Dutra and Thomas (1998) advanced a working hypothesis on low adult returns to Horse Linto Creek in 1998:

" This may be related to flooding which occurred in this watershed during the winter of 1994-95. As cited in the Lower Trinity Ranger District downstream migrant final report, 103 salmon redds were counted in the Horse Linto watershed in the fall of 1994, which is not a low number. Subsequent downstream migrant trapping in the spring of 1995 and direct observation dives found extremely low numbers of young of the year (YOY) chinook. A total of 113 YOY chinook and 1,606 YOY steelhead (Oncorhynchus mykiss) were captured in the trap. Either the redds were damaged by the extreme high flows or most of the fish left the stream before the trap was operational. Based on this data and the subsequent low returns, it seems likely that the flooding of 94-95 impacted the number of four year old salmon returning to the Horse Linto watershed during the 1998-99 season."

Dutra and Thomas (1999) also made the following observation about age structure of 1998 Horse Linto Creek fall chinook spawners: "In fact, 1998-99 found the largest return of five year olds to date even though, four year old returns were depressed by flooding in 1995 possibly giving the false impression of a greater percentage of five year old returns, and the 1998-99 season experienced one of the smallest runs of the decade. It is not known why a greater number of fish held over in the ocean an additional year before returning to spawn. These growth and migration observations may be attributed to the El Nino event that occurred in 1997-98."

Dutra and Thomas (1999) made similar assertions with regard to Willow Creek 1998 fall chinook redd counts: "Downstream migrant numbers in 1995 for YOY chinook in Willow Creek were very low apparently due to the flooding that occurred that winter in this and other watersheds. This flooding, as stated previously, may have affected the number of returning four year old chinook, thus contributing to the low spawning activity. Also, Willow Creek continues to be affected by sediment input, which is a consequence of its proximity to a major highway; this has been a chronic factor which probably limits both spawning and rearing. It is difficult to assess the affects of instream enhancement work on fish habitat within Willow Creek when juxtaposed with the on-going sediment problem."