Unique Characteristics of Riverine Spawning Pygmy Whitefish

The Cedar River Municipal Watershed is a major source of high quality drinking water for the City of Seattle. The main reservoir, Chester Morse Lake, provides habitat for a unique population of adfluvial bull trout (Salvelinus confluentus), federally listed as threatened, and pygmy whitefish (Prosopium coulterii), one of their main food resources. Concurrent research and monitoring efforts are being conducted by SPU to document pertinent aspects of both species’ lacustrine and riverine ecology in order to support resource management and habitat restoration strategies. We used PIT (passive integrated transponder) technology to document spawning behavior of pygmy whitefish in selected major tributaries.  Over five separate winter spawning seasons (2006 – 2010), 2,512 pygmy whitefish were captured from the river during spawning, PIT tagged, and released. Many of these fish returned to spawn and were detected at an instream PIT tag antenna array during subsequent years.  We present preliminary data showing the length of time fish spend in tributaries, and intriguing new data on recurring spawning by tagged individuals over the last five spawning seasons.  To our knowledge, these data are the first to document individual spawning behavior for the species.