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Riedel T.E.,University of California at Los Angeles | Thulsiraj V.,University of California at Los Angeles | Zimmer-Faust A.G.,University of California at Los Angeles | Dagit R.,Resource Conservation District of the Santa Monica Mountains | And 7 more authors.
Water Research | Year: 2015

Elevated levels of fecal indicator bacteria (FIB) have been observed at Topanga Beach, CA, USA. To identify the FIB sources, a microbial source tracking study using a dog-, a gull- and two human-associated molecular markers was conducted at 10 sites over 21 months. Historical data suggest that episodic discharge from the lagoon at the mouth of Topanga Creek is the main source of bacteria to the beach. A decline in creek FIB/markers downstream from upper watershed development and a sharp increase in FIB/markers at the lagoon sites suggest sources are local to the lagoon. At the lagoon and beach, human markers are detected sporadically, dog marker peaks in abundance mid-winter, and gull marker is chronically elevated. Varied seasonal patterns of FIB and source markers were identified showing the importance of applying a suite of markers over long-term spatial and temporal sampling to identify a complex combination of sources of contamination. © 2014 Elsevier Ltd.

McLaughlin K.,Southern California Coastal Water Research Project | Sutula M.,Southern California Coastal Water Research Project | Busse L.,San Diego Regional Water Quality Control Board | Anderson S.,California State University, Channel Islands | And 5 more authors.
Estuaries and Coasts | Year: 2014

The magnitude and extent of eutrophication was assessed at 27 segments in 23 estuaries in the Southern California Bight (SCB) between October 2008 and 2009. We applied thresholds from the existing assessment frameworks from both the European Union and the U.S. National Eutrophication Assessment to measurements of three indicators [macroalgae biomass and cover, phytoplankton biomass, and dissolved oxygen (DO) concentration] to categorize eutrophic condition in each estuary. Based on these frameworks, a large fraction of segments had moderate or worse eutrophic condition-78 % based on macroalgae, 39 % for phytoplankton, and 63 % for DO. Macroalgal biomass exceeding 70 g dw m-2 and 25 % cover was found at 52 % of sites during any sampling event and in 33 % of segments for 8 weeks or longer, a duration found to negatively impact benthic infauna. Duration of hypoxic events (DO < 4 mg L-1) was typically short, with most events less than one day; although 53 % of segments had at least one event longer than 24 h. Assessment frameworks of eutrophic condition are likely to evolve over time as the body of literature on eutrophication grows, including aspects such as the applicability of indicators in specific habitat types, indicator thresholds, and how event frequency and duration are incorporated. This paper informs this debate by discussing how eutrophic conditions in SCB estuaries are categorized using different indicators and thresholds. To this end, categorization of estuarine eutrophic condition was found to be very sensitive to the type of threshold, how data are integrated to represent duration or spatial extent, and how indicators are used as multiple lines of evidence. © 2013 Coastal and Estuarine Research Federation.

Dagit R.,Resource Conservation District of the Santa Monica Mountains | Krug J.,Resource Conservation District of the Santa Monica Mountains
North American Journal of Fisheries Management | Year: 2016

As part of a 7-year lifecycle monitoring study, electroshocking was used to capture and characterize a small population of federally listed endangered southern California steelhead Oncorhynchus mykiss in Topanga Creek, Los Angeles, California. Electroshocking is a tool widely used to study fish populations, despite its potential behavioral and physical effects on individuals. We examined rates of external hemorrhaging (i.e., branding) and its effect on growth rates and survival of recaptured individuals. Rates of branding were low (0–3%) during most November events from 2008 to 2014, but higher during all March events (8–23%) and during the November 2011 event (13%). Overall, 5% of the total captured individuals exhibited branding. Growth rates (mm/d) of individuals recaptured after branding were not significantly different, but on average were 9% lower than average daily growth rates for individuals in the same size-class captured and recaptured in the same time periods. In general, larger fish were more likely to be branded than were smaller fish (P < 0.0001). Although 69% of brandings occurred in pool habitats, which tend to be larger and deeper than other habitats, branding was not significantly more likely to occur in any habitat type (P = 0.13) or in any substrate type (P = 0.16), and mean or maximum depth of habitat was not related to the rate of branding. The population-level effects associated with branding remain unclear. Although important information has been obtained through the use of electroshocking, the cumulative effects of electroshocking-induced injuries to this endangered species need to be considered. Received March 2, 2015; accepted March 27, 2016 Published online July 19, 2016 © American Fisheries Society 2016.

Bell E.,Stillwater science | Albers S.M.,Resource Conservation District of the Santa Monica Mountains | Krug J.M.,Resource Conservation District of the Santa Monica Mountains | Dagit R.,Resource Conservation District of the Santa Monica Mountains
California Fish and Game | Year: 2011

The life hisTories of Oncorhynchus mykiss populations in the southern portion of their range have received less attention than in the Pacific Northwest, and have only recently been the subject of focused studies. Here we examine size-at-age data collected from O. mykiss in Topanga Creek, Los Angeles County, California, where research has been conducted for nearly a decade. Our results suggest that all age classes of resident and anadromous O. mykiss in Topanga Creek grow yearround despite high summer water temperatures. In addition, age 2 steelhead smolts attain a size that has been associated with high (>10%) marine survival in other studies.

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