Colonization and Persistence of a Southern California Steelhead (Oncorhynchus mykiss) population

Abstract.-The life history and habitat interactions of southern Oncorhynchus mykiss populations have received less attention than their Pacific Northwest counterparts. In this article we create a conceptual model describing the factors affecting O. mykiss population dynamics in Topanga Creek, Los Angeles County, California to understand the process that led to extirpation following floods in 1980 and 1983, re-colonization in the late 1990's, and continued persistence. We conclude that key factors influencing population dynamics include life-history variability with both resident and anadromous individuals, population spatial structure connecting Topanga Creek with other watersheds within the metapopulation, exclusive distribution within the mainstem Topanga Creek, high-quality summer and winter rearing habit, and food availability sufficient to maintain growth at high temperatures. Protecting the population in Topanga Creek from future extirpation should include restoration of the lagoon, and preventing changes to the flow regime and water quality

Ichthyofauna of the Los Angeles River

The Los Angeles River is a highly modified urban system. Upper tributaries of the watershed are located in Angeles National Forest and are in a relatively natural state, but below the forest boundary the tributaries and the mainstem consist of a series of completely channelized sections with a concrete bottom that includes a low-flow channel and vertical walls, sections where there are graded berms and a substrate that was either not stabilized with a concrete substrate, or where enough sediment has accumulated to provide a “soft-bottom” with vegetation, boulders, and variation in flow, and off-channel impoundments. Here we provide the results of fish surveys and both professional and community-contributed citizen science observations collected from 2007-2020 that document the presence of 29 species, of which six, found either in upper reaches (sections of the river with similar habitat and hydrologic characteristics) or in the estuary, are native to the river. To accompany these data, we also provide a novel classification schema identifying the unique reaches of the LA River

A longitudinal temperature profile of the Los Angeles River from June through October 2016

This pilot study developed a longitudinal temperature profile of the Los Angeles River by deploying temperature loggers throughout the watershed between June and October 2016. The watershed was divided into zones based on river system component, urbanization, and channelization. Channelized sites recorded the highest temperatures, tributaries recorded the lowest, and the estuary showed the most fluctuation. Overall, temperatures were too warm to support re-introduction of native fish but currently support non-native fish species. Temperature mitigation is needed for native species to re-establish. Albeit limited in scope, this study establishes a baseline of summer/fall temperatures in the Los Angeles River

The effects of a prolonged drought on southern Steelhead Trout (Oncorhynchus mykiss) in a coastal creek, Los Angeles County, California

Long-term lifecycle monitoring of federally endangered southern steelhead trout (Oncorhynchus mykiss) in Topanga Creek provides a unique opportunity to examine the health and abundance of a steelhead population before (2008-2011) and during (2012-2016) a prolonged drought. We found that the five-year drought resulted in a substantial and significant decline in available wetted habitat suitable for rearing and upstream migratory access for anadromous adults. The response of the steelhead population has been a significant reduction in anadromous spawning, distribution of rearing, and abundance of all life stages of anadromous and resident steelhead. After five years of drought a population that exceeded 325 individuals in 2008, now numbers fewer than 50 fish, and appears to be at extremely high risk of extirpation. Acknowledging the possibility of increased drought regionally and globally, the need to bolster southern steelhead resiliency to additional disturbance is paramount