## 1 Introduction  
Migrating fish may be injured or killed when they pass through hydroturbines and other passage routes at hydroelectric facilities [1-6]. In the Columbia and Snake River basins, several species of anadromous Pacific salmon are currently listed for protection under the Endangered Species Act of 1973 due to population declines. The 2008 Federal Columbia River Power System Biological Opinion (FCRPS BiOp; [7]) includes standards to be met to make hydroelectric facilities more fish-friendly through operational changes, improved hydroturbine design, and other structural or operational changes. Implementing and testing these changes require reliable estimates of behavior, timing, and survival of the juvenile salmonids as they migrate downstream through the FCRPS and into the Pacific Ocean [8-11].  
The Juvenile Salmon Acoustic Telemetry System (JSATS) is a nonproprietary sensing technology developed by the U.S. Army Corps of Engineers (USACE), Portland District, for evaluating behavior and survival of juvenile salmonids migrating through the FCRPS. Receivers have been deployed at large hydroelectric dams, in free-flowing sections of the FCRPS, and in the estuary of the Columbia River [12]. The JSATS consists of acoustic microtransmitters; autonomous, cabled, or portable receivers with hydrophones; and data management and processing applications.  
Self-contained autonomous receivers that detect, decode, and store decoded messages are typically deployed in areas within the Columbia River basin where a power source is not readily available and cable runs are not feasible [12,13]. General fisheries applications of JSATS and the autonomous receivers were reported in 2010 [12]. Portable receivers detect, decode, store, and display transmitted signals for in-laboratory transmitter testing and for displaying and entering transmitter codes at the time of tagging. A mobile receiver consisting of a single four-hydrophone cluster deployed from a mobile platform (e.g., a single boat) has been used to provide two-dimensional (2D) and three-dimensional (3D) position estimates on actively migrating tagged fish. Cabled receivers detect, decode, and store decoded messages, time of arrival (TOA), and message waveforms as received, on up to four hydrophones per four-channel receiver system. These receivers are typically located at large hydroelectric dams within the FCRPS and are used for estimating route and time of passage, including 2D and 3D position estimates for tagged fish. TOA information for valid detections on at least four hydrophones is required to solve for 3D position, and TOA information from at least three hydrophones is required to resolve for 2D position [14-21]. Cabled receivers are intended for deployment primarily at dams or other locations where cabled hydrophones can be deployed, electricity is available, equipment can be maintained without undue logistical complexity or cost, and immediate access to received transmitter messages is desirable. The cabled receivers also provide synchronization and high accuracy in the time of receipt of transmitter messages across an array of many hydrophones when required. In addition to fixed-location hydrophone arrays, cabled receivers also satisfy requirements for mobile arrays that may be deployed in fixed geometries from boats.  
In this article, we describe in detail the engineering design and implementation of the current version of the JSATS cabled system. In Part 2 [22], 3D tracking and error analysis using JSATS cabled systems are presented and evaluated.