Experimental Fish Guidance Devices

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Experimental Fish Guidance Devices

Position statement

By: National Marine Fisheries Southwest Division

Date: January 22, 1999

Source: National Marine Fisheries Southwest Division. "Experimental Fish Guidance Devices." January 22, 1999.

About the Author: The National Marine Fisheries Service (NMFS) is part of the National Oceanographic and Atmospheric Administration (NOAA), which is supported through the Department of Commerce. The Southwest Division of NMFS is located in Long Beach, California, and is responsible for the management, conservation and protection of marine species and habitats off the coast of California. It serves as both a scientific and policy resource.


For more than 300 years, Americans have used rivers, streams, and other waterways as a means of transport, for irrigation, and as a source of electricity and drinking water. People developed many different methods of changing the course of flowing water so that their own purposes could be served. For example, rivers are dammed to produce lakes and to generate electricity from the movement of water. Dykes are built to control flooding. Culverts are constructed to divert water and prevent erosion. Water diversions are used to move water into agricultural areas for irrigation.

The fish that live in the rivers are dependent on the flow of the river for their survival. Most species of fish that live in rivers and streams lay their eggs in one location and then migrate to another region of the river to feed. Juveniles often live in protected areas until they are large enough to forage in the open stream. Dams, dykes, culverts, and other manmade obstructions impede the ability of many fish to carry out the necessary movements that allow for their survival. In particular, many juvenile fish are killed trying to pass through water diversions.

In 2003, the U.S. Fish and Wildlife Service estimated that there were more than 2.5 million water diversions in the United States and that 75,000 of them were more than 6 feet (1.8 meters) high. As agricultural practices have changed through the years, many of these water diversions no longer serve their intended purpose and are obsolete. However, they still affect fish populations by fragmenting important habitat areas.

Surveys of fish populations toward the end of the twentieth century showed that some populations of fish native to streams and rivers in the United States had disappeared. Other species were severely depleted in number. One major cause was the impact of dams and other water diversions. Biologists studied potential methods for reducing the mortality of fish that pass through water diversions by building screening devices, which are structures that allow fish to swim around the diversions unharmed.



Introduction Numerous stocks of salmon and steelhead trout in California streams are at low levels and many stocks continue to decline. The Sacramento River winter-run chinook salmon is listed as "endangered" under the Federal Endangered Species Act. Petitions for additional listings are pending. It is essential to provide maximum protection for juveniles to halt and reverse these declines.

The injury or death of juvenile fish at water diversion intakes have long been identified as a major source of fish mortality [Spencer 1928, Hatton 1939, Hallock and Woert 1959, Hallock 1987]. Fish diverted into power turbines experience up to 40 percent mortality as well as injury, disorientation, and delay of migration [Bell, 1991], while those entrained into agricultural and municipal water diversions experience 100 percent mortality. Diversion mortality is the major cause of decline in some fish populations.

Positive barrier screens have long been tested and used to prevent or reduce the loss of fish. Recent decades have seen an increase in the use and effectiveness of these screens and bypass systems; they take advantage of carefully designed hydraulic conditions and known fish behavior. These positive systems are successful at moving juvenile salmonids past intakes with a minimum of delay, loss or injury.

The past few decades have also seen much effort in developing "startle" systems to elicit a taxis (response) by the fish with an ultimate goal of reducing entrainment. This Position Statement addresses research designed to prevent fish losses at diversions and presents a tiered process for studying, reviewing, and implementing future fish protection measures.

Juveniles at Intakes The three main causes of delay, injury, and loss of fish at water intakes are entrainment, impingement, and predation. Entrainment occurs when the fish is pulled into the diversion and passes into a canal or turbine. Impingement is where a fish comes in contact with a screen, a trashrack, or debris at the intake. This causes bruising, descaling, and other injuries. Impingement, if prolonged, repeated, or occurs at high velocities also causes direct mortality. Predation also occurs. Intakes increase predation by stressing or disorienting fish and/or by providing habitat for fish and bird predators.

A. Positive Barriers Positive barrier screen systems and criteria for their design have been developed, tested, and proved to minimize harm caused at diversions. Positive barriers do not rely on active fish behavior; they prevent physical entrainment with a physical barrier. Screens with small openings and good seals are designed to work with hydraulic conditions at the site, providing low velocities normal to the screen face and sufficient sweeping velocities to move fish past the screen. These screens are very effective at preventing entrainment [Pearce and Lee 1991]. Carefully designed bypass systems minimize fish exposure to screens and provide hydraulic conditions that return fish to the river, preventing both entrainment and impingement [Rainey 1985]. The positive screen and fish bypass systems are designed to minimize predation, and to reduce mortality, stress, and delay from the point of diversion, through the bypass facility, and back the river.

Carefully designed positive barrier screen and bypass systems have been installed and evaluated at numerous facilities [Abernethy et al 1989, 1990, Rainey, 1990, Johnson, 1988]. A variety of screen types (e.g. flat plate, chevron, drum) and screen materials (e.g. woven cloth, perforated plate, profile wire), have proved effective, taking into consideration their appropriateness for each site. Well-designed facilities consistently result in a guidance efficiency of over 95 percent [Hosey, 1990, Neitzel, 1985, 1986, 1990 a,b,c,d, Neitzel, 1991].

The main drawback to positive barrier screens is cost. At diversions of several hundred cubic feet per second or greater, the low velocity requirement and structural complexity can drive the cost for fish protection and the associated civil works over a million dollars. At the headwork, the need to clean the screen, remove trash, and provide regular maintenance (e.g. seasonal installation, replacing seals, etc.) also increase costs.

B. Behavioral Devices Due to higher costs of positive barrier screens, there has been much experimentation since 1960 to develop behavioral devices as a substitute for barrier screens [EPRI, 1986]. A behavioral device, as opposed to a positive (physical) barrier, requires a volitional taxis on the part of the fish to avoid entrainment. Early efforts were designed to either attract or repel fish. These studies focused on soliciting a behavioral response from the fish, usually noticeable agitation. Using these startle investigations to develop effective fish guidance systems has not been effective.

Experiments show that there is a large response variation between individual fish of the same size and species. Therefore, it cannot be predicted that a fish will always move toward or away from a certain stimulus. Even when such a movement is desired by a fish, it often cannot discern the source or direction of the signal and choose a safe escape route.

Many behavioral devices do not incorporate and use a controlled set of hydraulic conditions to assure fish guidance, as does the positive screen/bypass system. The devices can actually encourage fish movement that actually contrasts with the expected rheotactic response. Thus, the fish gets mixed signals about what direction to move. Another concern is repeated exposure; a fish may no longer react to a signal that initially was an attractant or repellant. In addition to the vagaries in the response of an individual fish, behavior variations are expected due to size, species, life stage, and water quality conditions.

In strong or accelerating water velocity fields, the swimming ability of a fish may prevent it from responding to a stimulus even if it attempts to do so. Other environmental cues (e.g., pursuing prey, avoiding predators, or attractive habitat) may cause a fish to ignore the signal.

A main motivation for opting to install behavioral devices is cost-savings. However, much of the cost in conventional systems is for the physical structure needed to provide proper hydraulic conditions. Paradoxically, complementing a behavioral device with its own structural requirements may lessen much of its cost advantage.

Present skepticism over behavioral devices is supported by the fact that few are currently being used in the field and those that have been installed and evaluated seldom exhibit consistent guidance efficiencies above 60 percent [Vogel, 1988, EPRI, 1986]. The louver system is an example of a behavioral device with a poor success record. In this case, even with the use of favorable hydraulics, performance is poor especially for smaller fish. Entrainment can be high, particularly when operated over a wide range of hydraulic conditions [Vogel, 1988, Cramer, 1982, Bates, 1961]. Due to their poor performance, some of these systems are already replaced by positive barriers….


In response to research into fish screening devices in the 1990s, which showed that the devices increased the survivorship of many fish species, Congress established the National Fish Passage Program in 1999. The goal of the program was to restore native fish populations to self-sustaining levels by allowing them to move throughout their natural habitat. At the same time, the program was sensitive to preventing the spread of introduced species by providing them with additional habitat. The program is broken up into seven regional offices, along with an administration in Washington D.C.

The National Fish Passage Program is a voluntary partnership between governmental agencies, private groups, and landowners. Costs are shared among these groups. Historically, the program has contributed approximately 27 percent of the cost for developing and installing fish screening devices, while the partners pay for the balance. Between 2000 and 2002, the program was funded at just over $1.5 million per year.

The National Fish Passage Program employs fisheries biologists who survey rivers and streams and produce a set of recommendations for sites that will best improve habitat for the most endangered species of fish. The information collected by the scientists is assimilated in a database called the Fish Passage Decision Support System. This system incorporates information on the location of water barriers, fish habitat and movement, benefits of building fish screening devices, cost of fish screening devices, and feasibility. The system relies on a geographical information system (GIS) to map all of this information. Analyses generated by the system is used to prioritize projects that will be undertaken by the Fish Passage Program.

Within three years, the program supported 105 fish passage projects in twenty-five states. The program partnered with 166 different agencies and saw significant benefits to fish populations throughout the country. Eighteen species of fish that were either endangered or threatened were directly impacted. The natural flow of water and natural water temperatures were reestablished for populations of trout, herring, striped bass, shad, sturgeon, salmon, minnows, and darters. Over 3,750 miles of river and nearly 70,000 acres of wetlands were restored as a result of the National Fish Passage Program.

Restoring natural river flows has benefits to other members of the ecosystem as well as the fish. Birds that eat fish, such as eagles, ospreys, and kingfishers have improved habitat in which to forage for food. Larger predators like bears, otters, and mink also enjoy larger prey populations. In addition, recreational, commercial, and subsistence fishermen benefit from larger fish populations that are spread out over a wider area.


Web sites

Hartlerode, Ray, Steve Allen, and Annette Dabashinsky. "John Day Fish Passage and Screening." 〈http://www.efw.bpa.gov/publications/H00005122-1.pdf〉 (accessed January 6, 2006).

Kepshire, Bernie. "Oregon Department of Fish and Wildlife Fish Screening Program: Fish Screen Types and Costs." 〈http://www.st.nmfs.gov/st5/Salmon_Workshop/20_Kepshire.pdf〉 (accessed January 6, 2006).

Oregon Department of Fish and Wildlife. "Fish Screening." 〈http://www.dfw.state.or.us/ODFWhtml/InfoCntrFish/PDFs/BKGFishScreen.pdf〉 (accessed January 6, 2006).

U.S. Fish and Wildlife Service. "National Fish Passage Program." 〈http://www.fws.gov/fisheries/FWSMA/fishpassage〉 (accessed January 6, 2006).

U.S. Fish and Wildlife Service—Pacific Region. "Fish Passage/Screening Program FRIMA." 〈http://www.fws.gov/pacific/Fisheries/Fish%20Passage-Screening%20Program.htm〉 (accessed January 6, 2006).

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