Mark Jessop’s research while affiliated with National Oceanic and Atmospheric Administration and other places

Monitoring trends in abundance of Endangered Species Act (ESA) listed adult steelhead (Oncorhynchus mykiss) is essential to assessing their viability. However, in central and southern California (the southern extent of their range), monitoring is difficult due to the low abundance and patchy distribution of adults. The only successful method has been counting stations at barriers (e.g., dams, weirs, etc.) that involve a certain amount of ESA “take” in handling listed fish. As a new alternative that avoids “take,” we have successfully used dual-frequency identification sonar (DIDSON) for monitoring adult steelhead abundance (Pipal et al. In press). The operational aspects of using DIDSON to monitor small fish populations in a more urbanized setting are different than for its more common use to enumerate large runs of salmon in more remote regions. We have deployed DIDSON in three different locations in central California to monitor steelhead and have gained significant insight into the necessary operational considerations. These are described here in detail and include the following:  site selection  DIDSON unit configuration  deployment and system security  data management (recording, processing and storage)  species identification  and data analyses, which include a Decision Support Tool used to standardize fish counts .We also identify areas needing further research, particularly species identification, and offer suggestions for possible solutions.

Steelhead, Oncorhynchus mykiss, are currently listed under the United States Endangered Species Act (ESA) in central and southern California. In most of this region, steelhead are considered threatened, but the Southern California Distinct Population Segment (DPS), comprising populations in Santa Barbara County and southward is listed as endangered, with only very small numbers of steelhead reported from the Santa Maria River south to the United States-Mexico border (Good et al. 2005). The listings are based mainly on anecdotal information of adult steelhead abundance, with the exception of escapement estimates based on dam counts on the Carmel River (part of the South-Central California Coast DPS), and recently initiated monitoring efforts in two tributaries of the Santa Ynez River system and on the mainstem of the Ventura River (part of the Southern California Coast DPS). Knowledge of whether a species' abundance is increasing or decreasing is essential to assessing the effectiveness of management and recovery actions under the ESA. Consequently, the need to initiate steelhead monitoring programs in central and southern California is critical. However, the need to monitor abundance of this oftentimes rare species in these regions is beset by a number of technical challenges. First, the low abundance and potentially highly patchy distribution of spawners demand that a higher fraction of available habitats be sampled to achieve a particular level of precision. Additionally, many watersheds in California's coastal region are characterized by highly erodible soil types and extremely dynamic hydrographs, which produce high turbidity and otherwise difficult conditions for conducting conventional spawner, redd, or carcass surveys. These conditions suggest that use of video or other visual monitoring that targets adults in migration corridors downstream of known spawning areas may be more efficient, although such efforts are likewise hindered by the flashiness and turbidity typical of high-order streams in coastal California. The National Marine Fisheries Service (NMFS) has operated a floating resistance panel weir on Scott Creek (Santa Cruz County) to estimate coho salmon, Oncorhynchus kisutch, and steelhead escapement since 2004 (Bond et al. 2008). However, this is the only attempt at using such a device in a California coastal stream with a dominant substrate of mudstone and sand, both of which are easily transported during high flow events and can thus render such a weir inoperable during fish migration periods. Additionally, construction of weirs or other structures for the purpose of counting fish is likely to be undesirable, as these structures may impede or hinder the spawning migrations of populations that are close to extinction. In this paper, we introduce and provide a preliminary evaluation of a sonar-based approach that addresses the difficulties of monitoring rare or endangered salmonids. Dual-frequency identification sonar (DIDSON) uses high-frequency sound waves to produce California Fish and Game 96(1): 90-95; 2010