Evaluation of juvenile salmon behavior at Bonneville Dam, Columbia River, using a multibeam technique

Abstract

In recent years, with increased effort to bypass and guide fragile stocks of juvenile salmon in the Columbia Basin past hydroelectric projects, it has been increasingly important to obtain fine-scale fish behavior data in a non-intrusive manner. The Dual-Head Multibeam Sonar is an emerging technology for fisheries applications that addresses that requirement. It has two principal advantages over traditional hydroacoustic techniques: 1) it allows for simultaneous large-volume coverage of a region of interest, and 2) it affords three-dimensional tracking capability. The use of Dual-Head Multibeam Sonar in this study resulted in an unprecedented insight into fine-scale smolt behavior upstream of a prototype surface collector at the Bonneville Dam first powerhouse in 1998. Our results indicated that outmigrant juvenile salmon had an increased likelihood of milling or holding. This discovery will lead to better design criteria for future bypass and collector systems. Future fisheries multibeam sonar systems will likely be fully integrated systems with built-in real-time tracking capability. These systems may be used to track targets relative to physical guidance structures or other behavior-modifying stimuli such as light, turbulent flow, electrical/magnetic fields, or low-frequency sound and vibration. The combination of fine-scale fish behavior data and environmental parameters will yield better design criteria for the safe passage of listed or endangered species of Pacific salmon.

Résumé

Ces dernières années, avec l'effort croissant d'aménagement pour faciliter et guider le passage des saumons juvéniles au niveau des barrages hydroélectriques du fleuve Columbia, il est devenu de plus en plus important d'obtenir des données précises sur le comportement des saumons sans provoquer de dommage corporel aux poissons. Le sonar multifaisceaux à deux têtes est une nouvelle technologie qui permet cette application. Il a deux principaux avantages sur les techniques hydroacoustiques traditionnelles : 1) de grands volumes peuvent être considérés simultanément, 2) il permet un suivi en trois dimensions. L'utilisation de ce sonar dans cette étude a permis d'observer pour la première fois le comportement, à petite échelle, des smolts en amont, au niveau d'un prototype d'un système de collecteur en surface. Nos résultats indiquent que les saumons juvéniles en migration ont une probabilité qui va croissante de se faire happer par les turbines ou piéger. Cette découverte conduira à mieux définir les paramètres des futurs systèmes de collecteurs et de passes à saumons. Les systèmes de sonar multifaisceaux utilisés en pêche devront intégrer des systèmes permettant le suivi des poissons en temps réel. Ces systèmes pourraient être utilisés pour guider des poissons avec des barrières physiques ou en utilisant des stimulus qui modifieraient le comportement tels que la lumière, des courants tourbillonnaires, des champs magnétiques ou électriques ou bien des vibrations et sons à basse fréquence. La combinaison entre des données de comportement des poissons à petite échelle et de paramètres environnementaux donneront de meilleurs critères pour la réalisation de passes à poisson pour les espèces en danger telles que le saumon du Pacifique.

Introduction

The Portland District of the U.S. Army Corps of Engineers (Corps) began developing surface flow bypass and collection systems in 1995, in response to the 1995 biological opinion on the operation of the federal Columbia River power system (National Marine Fisheries Service, 1995). Because of this mandate, the Corps began an aggressive, nontraditional development of surface flow bypass concepts with a sense of urgency for design, construction, and testing U.S. Army Corps of Engineers, 1995, Johnson et al., 2000.

The Corps has conducted evaluations of surface flow bypass concepts for outmigrant juvenile salmonids for a number of years. One objective is to provide passive attraction or guidance flows to the salmonids and understand their behavior as they approach bypass structures, whether surface bypass structures retrofit to a dam or blocked trash racks and sluice chutes. Understanding the behavior of fish in front of these bypass and guiding structures will play a major role in helping engineers design permanent structures.

A number of different types of devices have been used in past years to try to understand the behavior of downstream-migrant fish. These include direct capture, video, radio telemetry, and sonic telemetry. Because many of the stocks in question are currently listed under the Endangered Species Act, techniques involving direct capture are limited. Video has met with limited success because of the relatively high turbidity levels associated with spring runoff. Video is best applied in close proximity to a structure, and thus, yields little information on the fish’s approach behavior. Radio telemetry, while not functionally limited in range, does not provide the information necessary for fine-scale behavioral evaluations. In recent years, the emergence of tag tracking systems, suitable for freshwater applications, has gained favor with researchers. However, current tag technology requires use of a relatively large tag (7 mm × 16 mm), which may affect fish behavior, particularly for 0-age salmonid smolts. Because of the shortfalls of traditional methods and current limitations of new telemetry methods, it was desirable to pursue a new, non-intrusive technique for evaluating juvenile migrant salmon behavior near prototype bypass structures.

This paper describes a new technique, Dual-Head Multibeam Sonar (U.S. Patent 6,084,827, issued July 4, 2000), for obtaining fine-scale fish behavior near prototype surface collector and guidance structures at hydropower projects.