Juvenile Salmonid Migratory Behavior at the Mouth of the Columbia River and within the Plume

Juvenile salmonids tagged in the Columbia River with small acoustic transmitters (weight = 0.43 g in air) were detected on a sparse array of Juvenile Salmon Acoustic Telemetry System (JSATS) autonomous receivers in the Columbia River plume in an effort to inform survival study experimental design. The 20-receiver ‘box-shaped’ array had ~3 km internode spacing with the terminus portion along the 100-m depth contour. A total of 1,680 unique JSATS-tagged juvenile salmonids were detected on the plume array between 5 May and 8 August 2010. Travel rates of juvenile Chinook salmon were slower upon ocean entry when compared to in-river movement rates. Juvenile steelhead travel rates increased upon ocean entry. Most yearling (86%) and subyearling (74%) Chinook salmon and steelhead (96%) moved from the mouth of the river to the plume array in 3 days or less. Subyearling Chinook salmon spent more time between the mouth of the river and their final detection on the plume array, with 20% taking more than 6 days to traverse this area. Tagged yearling Chinook salmon and steelhead were primarily detected on the terminus array, with more of the remainder being detected on the southern sub-array than on the northern sub-array prior to 18 May 2010. In the latter half of May, more yearling Chinook salmon and steelhead were last detected on the northern sub-array than on the southern sub-array; however the majority continued to be last detected on the terminus sub-array. Before 18 May, about 27 and 47% of the yearling Chinook salmon and steelhead, respectively, were last detected on the southern sub-array. From 18 May and later, 14 to 18% of each species was last detected on the southern sub-array. The distribution of tagged yearling Chinook salmon last detected moving north and south were skewed toward deeper waters farther off-shore in comparison to steelhead and subyearling Chinook salmon. Subyearling Chinook salmon were more often last detected on the northern sub-array (55%) and southern sub-array (23%), than they were on the terminus sub-array (22%). The 2010 pilot scale JSATS array deployment in the Columbia River plume was successful in terms of providing the necessary behavioral information to enable the design of a robust survival study of juvenile salmonids exiting the Columbia River.