Assessment of Salmonids and Their Habitat Conditions in the Walla Walla River Basin within Washington: 2001 Annual Report

This study began in 1998 to assess salmonid distribution, relative abundance, genetics, and the condition of salmonid habitats in the Walla Walla River basin.

Stream flows have shown a general trend that begins with a sharp decline in discharge in late June, followed by low summer flows and then an increase in discharge in fall and winter. The Walla Walla River saw continuous overland flow from Nursery Bridge in Oregon to the Washington/Oregon stateline, for the first time in decades, due to a 2000 settlement agreement with USFWS and the irrigation districts in Oregon. Manual stream flows at Pepper bridge showed an increase in 2001 of 300-400% from July-September, over the previous 3 years. The Washington Department of Fish and Wildlife (WDFW) also cooperated with the National Marine Fisheries Service (NMFS), Deparment of Ecology (DOE), the City of Walla Walla, the Walla Walla Flood Control District, the Corps of Engineers, the U.S. Fish and Wildlife Service (USFWS), and others on a test to increase and evaluate flows through the Mill Ck flood control channel. The purpose of the test was to try and eliminate a take of listed steelhead by diverting 3-12 cfs into the flood control channel.

Stream temperatures in the Walla Walla basin were similar to those in 2000. Upper montane tributaries held max summer temperatures below 65EF, while sites in mid and lower Touchet and Walla Walla rivers frequently had daily maximum temperatures above 68EF (high enough to inhibit migration in adults and juveniles, and to sharply reduce survival of embryos and fry). These high temperatures are possibly the most critical physiological barrier to salmonids in the Walla Walla basin, but other factors (turbidity, cover, lack of pools, etc.) also play a part in fish survival, migration, and breeding success. The increased flows in the Walla Walla (due to the 2002 settlement) did not show consistent improvements in temperatures over the years, but decreases in maximum temperatures were seen at Mojonnier Rd. and Swegel Rd. The test flow in Mill Ck on the other hand produced substantial increases in water temperature (10-20EF) from the Yellowhawk diversion to Roosevelt St., reaching leathal maximum temperatures over 90EF.

Rainbow/steelhead (Oncorhynchus mykiss) trout represent the most common salmonid in the basin. Other salmonids including; bull trout (Salvelinus confluentus), chinook salmon (Oncorhynchus tshawytscha), mountain whitefish (Prosopium williamsoni), and brown trout (Salmo trutta) had low densities, and limited distribution throughout the basin. The 2000 settlement on the Walla Walla River seems to have had some positive effects on salmonid survival. Densities have shown increases from the Washington/Oregon stateline to Mojonnier Rd., but densities below this were inconsistent (Table 8). Fish densities in Mill Ck seem to have been negatively affected by the test flow. Some fish mortalities were likely caused by the high temperatures (85-91EF) created by the increased flow. Fish were found throughout Mill Ck in June, but after the test flow from mid June through early July few rainbow/steelhead existed from the Yellowhawk diversion to 9th Ave, and from Gose St. downstream.

Steelhead spawning surveys in Washington found 30 redds in the Walla Walla River and its tributaries, and 124 redds on the Touchet River and its tributaries. Bull trout spawning surveys in the upper Touchet River tributaries found a total of 148 redds (84 in the Wolf Fork, 16 in the Burnt Fork, and 48 in the North Fork Touchet and its tributaries). The largest number of returning adult spring chinook to the Touchet River (31 adults at the Dayton trap) in several decades prompted us to initiate spawning surveys on the upper mainstem Touchet River, the North Fork, and the Wolf Fork. A total of 32 spring chinook redds were identified with the majority (23 redds) being found on the Wolf Fork.

We recommend several changes in study emphasis for 2002, such as increasing sampling in Mill Creek.