Die Off and Current Status of Southern Steelhead Trout(Oncorhynchus mykiss) in Malibu Creek, Los AngelesCounty, USA

摘要

A die-off of native and exotic fish and invertebrate species, including theendangered southern steelhead trout (Oncorhynchus mykiss) was observed in MalibuCreek, Los Angeles County, during the summer and fall of 2006. Death waspreceded by a period of illness during which trout in particular exhibited a noticeableyellow coloration. Physical, chemical and biological variables, including tempera-ture, dissolved oxygen, a variety of chemical contaminants, presence of toxinproducing algae, and direct pathology were examined but results remaininconclusive. The first day of a 12-day high temperature event occurred on thesame date yellow trout were first observed. This sustained event is different fromshorter term temperature spikes recorded in other years. Recovery monitoringdocumented re-colonization by all exotic fish species and crayfish, but limitednumbers of southern steelhead trout in 2007. Surveys in summer 2008 documented arecord number of anadromous adults (five silvery fish over 50 cm total length) andyoung of the year