Tracey W. Steig

Correcting bias in survival estimation resulting from tag failure in acoustic and radiotelemetry studies

The high detection rates of acoustic- and radio-tagged fish greatly improve the ability of an investigator to obtain information on survival and movement of fish with fewer tags. The trade-off, though, is a greater dependence on the individual tag performance, as each tagged fish in a smaller study represents a greater proportion of the outcome. This reduction in release size, due to the increase in detection capability, places a greater emphasis on the need to accurately gauge the status of the tagged fish. Should a tag fail while a smolt is migrating through the study area, the release-recapture model cannot discern the difference between smolt death and tag failure. If the release-recapture models are not adjusted for the probability of tag failure, the estimates of smolt survival will therefore be negatively biased. This article presents a semiparametric approach for adjusting survival estimates from release-recapture studies for tag failure, and provides subsequent estimation of sampling variance and its contributing components.

Improved techniques for studying the temporal and spatial behavior of fish in a fixed location

There are many situations when it is important to know accurately the behavior of fish as a function of time and space in a fixed, three-dimensional volume. One example is the optimal design of techniques that minimize the mortality of fish approaching hydroelectric dams or the cooling intakes of a power plant. The behavior of fish in other fixed volumes, such as estuaries and open rivers, is also of interest in the case of many migrating fish stocks. Both active (echosounding) and passive systems based on acoustic-emitting tags implanted in fish have been used to collect behavioral data. Active acoustic systems, including those with electronically and mechanically steered beams, only insonify a small part of the total volume of interest at any given time. Tag systems, on the other hand, can be used to monitor the behavior of tagged fish over the entire volume. A number of advances in the implementation, deployment, and analysis of acoustic-tag systems have been made over the past few years. These improvements include techniques for positioning optimally the receiving hydrophones to minimize the location measurement errors, the development of acoustic-signal waveforms that provide both unique target identification and accurate location estimates, and the development of tracking algorithms that associate and track the multiple returns from an individual fish. These various techniques are described. Guidelines are presented for selecting the various parameters for the tag system, including the positions of the hydrophones. Specific examples that compare the predicted and actual performance of the tag systems are described.

Review on monitoring adult salmonid (Oncorhynchus and Salmo spp.) escapement using fixed-location split-beam hydroacoustics

Since 1992, split-beam hydroacoustic techniques have been used to monitor adult salmonid escapement (Oncorhynchus and Salmo spp.) in 14 rivers in North America and Europe. Monitoring in rivers is one of the more challenging applications for fisheries acoustics. Rivers typically have a high reverberation level, uneven bottom bathymetry, and nonlaminar hydraulics, requiring sophisticated equipment and careful deployment, calibration, and testing. The major issues that were addressed in order to obtain estimates of adult salmon escapement included hydroacoustic equipment and techniques, site selection, transducer deployment, and fish behavior. Fixed-location hydroacoustic techniques were employed, utilizing narrow-beam transducers aimed horizontally, monitoring migrating fish in side-aspect. Fish were tracked in three dimensions as they passed through the acoustic beam. A bottom substrate of low acoustic reflectivity enabled the acoustic beam to be aimed close to the bottom. Sites were selected where fish were actively migrating, not holding or milling. In most cases, migrating salmonids were strongly shore- and bottom-oriented, where water velocities were slowest. Diel distributions of fish passage were weighted toward nighttime. Other results included fish size and velocity. Potential improvements in riverine monitoring capabilities include quadrature demodulation and FM Slide/Chirp signals.

A Multiple-Release Model to Estimate Route-Specific and Dam Passage Survival at a Hydroelectric Project

Abstract Previous methods of estimating route-specific passage and survival probabilities for anadromous salmonids past hydroelectric dams have often failed because of faulty assumptions. We present a robust, multiple-release model that combines release–recapture methods that are known to solve parts of the overall problem. Release 1 allows estimation of route-specific passage proportions and relative route-specific survival probabilities. Releases 2 and 3 provide an estimate of absolute survival through a particular route, which gives estimates of absolute route-specific survival probabilities and dam survival when combined with release 1. Releases 1 and 4 together provide an estimate of project (dam and pool) survival. Combining information from all four releases gives estimates of pool survival. The method is demonstrated through a 2006 study of sockeye salmon Oncorhynchus nerka passing Rocky Reach Dam on the Columbia River in Washington State. We estimate that the majority of tagged smolts passed via ...

Acoustic monitoring of salmonid density, target strength, and trajectories at two dams on the Columbia River, using a split-beam scanning system

Abstract Horizontal acoustic scanning was used at two hydropower dams on the Columbia River to monitor downstream migrating juvenile salmonids. Two split-beam systems with computer-controlled rotating capabilities monitored the fish movement patterns in the forebay areas of the Rocky Reach and Rock Island dams. Scanning consisted of 15 or 17 horizontal aiming angles, separated in 10° increments each monitored for 4 min, and tilted downwards from the horizontal at either 10° or 15°. Scanning was carried out for 24 h/day for periods of five days in May 1995 and was part of a larger study which lasted from 4–6 weeks. Estimates of mean fish density, target strength and trajectory were made for 5-m range cells within each horizontal scanning angle. Results show that fish movement patterns differed in the two dams. At Rocky Reach Dam, fish followed a circular trajectory pattern which was similar to the observed pattern of river flow and fish target strengths were higher in areas of low water velocity. At Rock Island Dam, fish behavior differed according to whether turbine units were operating or not. When turbines were in operation, fish moved towards the flow which contrasted with their milling behavior when the turbines were not operating. The fish target strengths were also greater in the latter situation. The difference in body aspect being insonified may account for this random acoustic aspect of milling fish compared with primarily head/dorsal aspect of fish oriented to the operational turbines.

Comparison of Two Alternative Approaches for Estimating Dam Passage Survival of Salmon Smolts

Abstract Traditional single and paired release–recapture models are incapable of providing unbiased estimates of dam passage survival because their assumptions can never be met. Nevertheless, regulatory requirements mandate the estimation of this important performance measure for migratory fish species passing through hydroprojects. We present a new release–recapture model that uses a virtual release of in-river migrants known to have arrived at the dam, combined with a paired release below the dam, to estimate dam passage survival. Analytical comparisons of the sampling precision of the proposed virtual–paired-release model and an established route-specific model found that the new approach was always more precise for equal release numbers of tagged fish. In a field trial at Rocky Reach Dam, Washington, using smolts of sockeye salmon Oncorhynchus nerka, the new approach estimated dam passage survival with more than twice the precision of the alternative method. The proposed virtual–paired-release design ...

Behavioral results from acoustically tagged fish using innovative techniques for analyzing three-dimensional data

Acoustic tags have been used to monitor the swimming patterns of downstream migrating salmon smolts approaching various dams on the Columbia River, USA. Downstream migrating yearling chinook (Oncorhynchus tshawytscha), steelhead (O. mykiss), sockeye (O. nerka), and sub-yearling chinook smolts were surgically implanted with acoustic tags. Fish were tracked in three-dimensions as they approached and passed into the turbine intakes, spillways, and surface bypass channel entrances at the dams during the spring and summer outmigrations of 2005-2009. A number of advances in the analysis methods, techniques and software have been made over the past several years. Some of these improvements include the development of fish density algorithms, stream trace modeling analysis, and advances in three-dimensional animation programs. Three-dimensional tracks of fish approaching the turbine intakes, spillways, and surface bypass channel entrances will be presented. Concentrations of fish passage will be presented as three-dimensional fish densities superimposed over dam structures.

Innovative techniques for analyzing the three‐dimensional behavioral results from acoustically tagged fish

Acoustic tags were used to monitor the swimming patterns of downstream migrating salmon smolts approaching various dams on the Columbia River, USA. Downstream migrating yearling chinook (Oncorhynchus tshawytscha), steelhead (Oncorhynchus mykiss), sockeye (Oncorhynchus nerka), and sub‐yearling chinook smolts were surgically implanted with acoustic tags. Fish were tracked in three‐dimensions as they approached and passed into the turbine intakes, spillways, and surface bypass channel entrances at the dams during the 2004 spring and summer outmigrations. A number of advances in the analysis techniques and software have been made over the past few years. Some of these improvements include the development of various fish density algorithms, stream trace modeling analysis, and advances of three‐dimensional animation programs. Three‐dimensional tracks of fish approaching the turbine intakes, spillways, and surface bypass channel entrances will be presented. Concentrations of fish passage will be presented as thr...

Development of a method for estimating the probability of detecting fish through a hydroacoustic beam

Active hydroacoustic sampling techniques are widely used to monitor fish densities and behavior in aquatic environments. Since the 1970s, this technology has been used to assess a wide range of fisheries-related questions, including upstream and downstream migrations, stock assessments, behavioral evaluations, and others. When properly applied, hydroacoustics is a powerful and effective fisheries assessment tool, providing high sampling coverage that is unobtrusive and nonselective. Like any sampling technique, an understanding of the factors potentially influencing the ability to detect organisms and quantify the sampled volumes with a hydroacoustic system enhances the ability to accurately interpret the results and derive quantitative estimates. Several factors can affect the probability of detecting fish using hydroacoustics. These include: 1) the sampling environment; 2) hydroacoustic system data collection methodology and parameters; and 3) characteristics and distribution of the fish being monitored. Interactions between these factors can influence both the ability to detect fish of a given minimum size and the effective sampling volume of the hydroacoustic system. This paper describes methods for estimating the probability of detecting a fish within a hydroacoustic beam under different conditions. Examples demonstrating the effect of each of these parameters on the ability to detect fish using hydroacoustics are presented.

New system for remotely monitoring the three‐dimensional movement of acoustically tagged fish

A passive acoustic tag system was developed to monitor the three‐dimensional movements of migrating fish with submeter resolution. The acoustic tag receiver monitors an array consisting of up to 16 omnidirectional hydrophones, with received signals synchronized to determine the arrival times for each pulse transmitted by the acoustic tag. Arrival times are then used to calculate the three‐dimensional position of a tagged fish as it moves through the array. Algorithms were developed to precisely calculate the three‐dimensional positions of the hydrophones, and of each acoustic tag. Over the last 4 years, this system was used at several dams in the United States. Most studies to date monitored downstream migrating juvenile salmonids as they approached and passed turbine intakes, spillways, and juvenile bypass systems at hydroelectric dams. Fish movement patterns were tracked in three dimensions over time, typically with submeter resolution. Tagged fish were 160–240 mm long. Acoustic tags were approximately 7 mm in diameter by 23 mm long, weighted 2 g, and transmitted at 307 kHz. Tag codes (up to 500), pulse width (typically 1–5 ms), and ping rate (typically 0.3–3 pings/s) were field programmable. Current tags incorporate signal encoding for an improved signal‐to‐noise ratio, and weigh as little as 1 g.