Martin L. Ahmann

Assessment of Barotrauma from Rapid Decompression of Depth-Acclimated Juvenile Chinook Salmon Bearing Radiotelemetry Transmitters

Abstract This study investigated the mortality of and injury to juvenile Chinook salmon Oncorhynchus tshawytscha exposed to simulated pressure changes associated with passage through a large Kaplan hydropower turbine. Mortality and injury varied depending on whether a fish was carrying a transmitter, the method of transmitter implantation, the depth of acclimation, and the size of the fish. Juvenile Chinook salmon implanted with radio transmitters were more likely than those without to die or sustain injuries during simulated turbine passage. Gastric transmitter implantation resulted in higher rates of injury and mortality than surgical implantation. Mortality and injury increased with increasing pressure of acclimation. Injuries were more common in subyearling fish than in yearling fish. Gas emboli in the gills and internal hemorrhaging were the major causes of mortality. Rupture of the swim bladder and emphysema in the fins were also common. This research makes clear that the exposure of juvenile Chinoo...

Quantifying Mortal Injury of Juvenile Chinook Salmon Exposed to Simulated Hydro-Turbine Passage

Abstract A proportion of juvenile Chinook salmon Oncorhynchus tshawytscha and other salmonids travel through one or more turbines during their seaward migration in the Columbia and Snake rivers. There is limited information on how these fish respond to the hydraulic pressures found during turbine passage events. We exposed juvenile Chinook salmon to varied acclimation pressures and subsequent exposure pressures to mimic the hydraulic pressures of large Kaplan turbines. Additionally, we varied abiotic (total dissolved gas and rate of pressure change) and biotic factors (condition factor, fish length, and fish weight) that may contribute to the incidence of mortal injury associated with fish passage through hydropower turbines. We determined that the main factor associated with the mortal injury of juvenile Chinook salmon during simulated turbine passage was the ratio between the acclimation pressure and the lowest exposure pressure. Condition factor, total dissolved gas, and rate of pressure change were fo...

The Influence of Tag Presence on the Mortality of Juvenile Chinook Salmon Exposed to Simulated Hydroturbine Passage: Implications for Survival Estimates and Management of Hydroelectric Facilities

Abstract Each year, telemetry tags (acoustic, radio, and passive integrated transponder tags) are surgically implanted into thousands of fish to assess their passage and survival through hydropower facilities. One passage route that is of particular concern is through hydroturbines, where fish may be exposed to a range of potential injuries that include barotraumas from rapid decompression. The change in pressure from acclimation to exposure (nadir) has been identified as an important factor in predicting the likelihood of mortality and injury for juvenile Chinook salmon Oncorhynchus tshawytscha undergoing rapid decompression associated with simulated turbine passage. The presence of telemetry tags has also been shown to influence the likelihood of mortality and injury for juvenile Chinook salmon. We investigated the likelihood of mortality and injury for telemetry-tagged juvenile Chinook salmon that were exposed to a range of pressure changes associated with simulated turbine passage. Several factors wer...

Improving hydroturbine pressures to enhance salmon passage survival and recovery

Barotrauma caused by rapid decompression during hydroturbine (turbine) passage may occur as fish move through the low pressure region below the turbine runner. This scenario is of particular concern in North American rivers with populations of ESA-listed salmon. The US Army Corps of Engineers (USACE) and the Pacific Northwest National Laboratory released Sensor Fish into lower Snake and Columbia River turbines to determine the magnitude and rate of pressure change fish might experience. Recorded pressures were applied to simulated turbine passage (STP) in laboratory studies to determine the effect of rapid decompression on juvenile Chinook salmon. These STP studies have increased our understanding of how pressure effects fish passing through turbines and suggest that the ratio of pressure change [acclimation pressure (the depth upstream of the dam where fish are neutrally buoyant) divided by nadir pressure (lowest pressure)] is highly predictive in determining the effect on smolt survival. However, uncertainty remains in smolt acclimation depth prior to entering turbine intakes at hydroelectric facilities. The USACE continues to make progress on salmon survival and recovery efforts through continued research and by applying pressure study results to turbine design. Designing new turbines with higher nadir pressure criteria is likely to provide safer fish passage for all salmonid species experiencing turbine passage.

A Field Evaluation of an External and Neutrally Buoyant Acoustic Transmitter for Juvenile Salmon: Implications for Estimating Hydroturbine Passage Survival

Turbine-passed fish are exposed to rapid decreases in pressure which can cause barotrauma. The presence of an implanted telemetry tag increases the likelihood of injury or death from exposure to pressure changes, thus potentially biasing studies evaluating survival of turbine-passed fish. Therefore, a neutrally buoyant externally attached tag was developed to eliminate this bias in turbine passage studies. This new tag was designed not to add excess mass in water or take up space in the coelom, having an effective tag burden of zero with the goal of reducing pressure related biases to turbine survival studies. To determine if this new tag affects fish performance or susceptibility to predation, it was evaluated in the field relative to internally implanted acoustic transmitters (JSATS; Juvenile Salmon Acoustic Telemetry System) used widely for survival studies of juvenile salmonids. Survival and travel time through the study reach was compared between fish with either tag type in an area of high predation in the Snake and Columbia rivers, Washington. An additional group of fish affixed with neutrally-buoyant dummy external tags were implanted with passive integrated transponder (PIT) tags and recovered further downstream to assess external tag retention and injury. There were no significant differences in survival to the first detection site, 12 river kilometers (rkm) downstream of release. Travel times were also similar between groups. Conversely, externally-tagged fish had reduced survival (or elevated tag loss) to the second detection site, 65 rkm downstream. In addition, the retention study revealed that tag loss was first observed in fish recaptured approximately 9 days after release. Results suggest that this new tag may be viable for short term (<8 days) single-dam turbine-passage studies and under these situations, may alleviate the turbine passage-related bias encountered when using internal tags, however further research is needed to confirm this.

Migration depth and residence time of juvenile salmonids in the forebays of hydropower dams prior to passage through turbines or juvenile bypass systems: implications for turbine-passage survival

We studied the depth and residence time of migrating juvenile salmonids in the forebays of hydropower dams before their passage through turbines or Juvenile Bypass Systems. This valuable information will increase our understanding of fish passage and help us identify possible management operations or better turbine designs.

Three-dimensional migration behavior of juvenile salmonids in reservoirs and near dams

To acquire 3-D tracking data on juvenile salmonids, Juvenile Salmon Acoustic Telemetry System (JSATS) cabled hydrophone arrays were deployed in the forebays of two dams on the Snake River and at a mid-reach reservoir between the dams. The depth distributions of fish were estimated by statistical analyses performed on large 3-D tracking data sets from ~33,500 individual acoustic tagged yearling and subyearling Chinook salmon and juvenile steelhead at the two dams in 2012 and subyearling Chinook salmon at the two dams and the mid-reach reservoir in 2013. This research investigated the correlation between vertical migration behavior and passage routes. The depth distributions of fish within the forebays of the dams were significantly different from fish passing the mid-reach reservoir. Fish residing deeper in the forebay tended to pass the dam using deeper powerhouse routes. This difference in depth distributions indicated that the depth distribution of fish at the mid-reach reservoir was not related to behaviors of fish passing through certain routes of the adjacent dams. For fish that were detected deeper than 17.5 m in the forebays, the probability of powerhouse passage (i.e., turbine) increased significantly. Another important finding was the variation in depth distributions during dam passage associated with the diel period, especially the crepuscular periods.