Anadromous fish at the arid urban edge - status of steelhead populations and habitat in Malibu Creek, Los Angeles County

Malibu Creek is a 109 square mile watershed at the north-western edge of the Los Angeles metropolitan area. Is it 22% developed, yet it supports one of the southern-most populations of endangered Oncorhynchus mykiss. This population is impacted by a number of impassible barriers including a large dam, the presence of numerous invasive species, anthropogenic pollution, and complex native geochemistry. A die-off of native and exotic fish and invertebrate species, including the endangered southern steelhead trout (Oncorhynchus mykiss) was observed in Malibu Creek, Los Angeles County, during the summer and fall of 2006. Physical, chemical and biological variables, including temperature, dissolved oxygen, a variety of chemical contaminants, presence of toxin producing algae, and direct pathology, were examined, but results remain inconclusive. A similar population decline was observed in 2009, sparking the development of a multifaceted investigation into possible causes including water quality, and the impact of aquatic invasive nuisance species, including a fairly recent invasion by the New Zealand mudsnail, Potamopyrgus antipodarum.