Richard L. Townsend

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.

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...

Statistical models for population reconstruction using age-at-harvest data

Statistical analyses based on maximum likelihood methods are presented to jointly estimate harvest rates, survival, recruitment, and population abundance from age-at-harvest data. To perform the population reconstruction from the age-at-harvest data, auxiliary field data and information on harvest reporting rates are required. The statistical methods permit tests of model assumptions, goodness-of-fit, and standard errors and confidence intervals for all estimated demographic parameters. We illustrate the methods using harvest data and radiotelemetry studies of elk (Cervus elaphus) from northern Idaho, USA, 1988-1993. We compare results with abundance estimates using an aerial sightability survey on the same herd. The maximum likelihood methods for age-at-harvest analysis provide a comprehensive framework for population reconstruction with abundance estimates comparable to field survey techniques.

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...

An Evaluation of Sex-Age-Kill (SAK) Model Performance

Abstract The sex-age-kill (SAK) model is widely used to estimate abundance of harvested large mammals, including white-tailed deer (Odocoileus virginianus). Despite a long history of use, few formal evaluations of SAK performance exist. We investigated how violations of the stable age distribution and stationary population assumption, changes to male or female harvest, stochastic effects (i.e., random fluctuations in recruitment and survival), and sampling efforts influenced SAK estimation. When the simulated population had a stable age distribution and λ > 1, the SAK model underestimated abundance. Conversely, when λ < 1, the SAK overestimated abundance. When changes to male harvest were introduced, SAK estimates were opposite the true population trend. In contrast, SAK estimates were robust to changes in female harvest rates. Stochastic effects caused SAK estimates to fluctuate about their equilibrium abundance, but the effect dampened as the size of the surveyed population increased. When we considered both stochastic effects and sampling error at a deer management unit scale the resultant abundance estimates were within ±121.9% of the true population level 95% of the time. These combined results demonstrate extreme sensitivity to model violations and scale of analysis. Without changes to model formulation, the SAK model will be biased when λ ≠ 1. Furthermore, any factor that alters the male harvest rate, such as changes to regulations or changes in hunter attitudes, will bias population estimates. Sex-age-kill estimates may be precise at large spatial scales, such as the state level, but less so at the individual management unit level. Alternative models, such as statistical age-at-harvest models, which require similar data types, might allow for more robust, broad-scale demographic assessments.

Calibrating Statistical Population Reconstruction Models Using Catch-Effort and Index Data

Abstract This paper illustrates how age-at-harvest data, when combined with hunter-effort information routinely collected by state game management agencies, can be used to estimate and monitor trends in big game abundance. Twenty-four years of age-at-harvest data for black-tailed deer (Odocoileus hemionus) were analyzed to produce abundance estimates ranging from 1,281 adult females to 3,232 adult females on a 22,079-ha tree farm in Pierce County, Washington, USA. The annual natural survival probability was estimated to be 0.7293 (= 0.0097) for this female population. The estimated abundance was highly correlated with an independent browse damage index (r = 0.8131, P < 0.001). A population reconstruction incorporating the browse index did not substantially improve the model fit but did provide an auxiliary model for predicting deer abundance. This population reconstruction illustrates a cost-effective alternative to expensive big game survey methods.

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...

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 Telemetry Evaluation of Juvenile Salmonid Passage and Survival at John Day Dam with Emphasis on the Prototype Surface Flow Outlet, 2008

The main purpose of the study was to evaluate the performance of Top Spill Weirs installed at two spillbays at John Day Dam and evaluate the effectiveness of these surface flow outlets at attracting juvenile salmon away from the powerhouse and reducing turbine passage. The Juvenile Salmonid Acoustic Telemetry System (JSATS) was used to estimate survival of juvenile salmonids passing the dam and also for calculating performance metrics used to evaluate the efficiency and effectiveness of the dam at passing juvenile salmonids.

Assessment of Subyearling Chinook Salmon Survival through the Federal Hydropower Projects in the Main-Stem Columbia River

AbstractHigh survival through hydropower projects is an essential element in the recovery of Pacific salmon Oncorhynchus spp. populations in the Columbia River. High dam passage survival is also a regulatory requirement under the 2008 Biological Opinion (BiOp; established under the Endangered Species Act) on Federal Columbia River Power System operation. The BiOp requires dam passage survival to be at least 0.96 and at least 0.93 for spring and summer out-migrating juvenile salmonids, respectively, and to be estimated with an SE of 0.015 or lower. An innovative virtual/paired-release design was used to estimate dam passage survival, which was defined as survival from the upstream face of a dam to the tailrace mixing zone. A coordinated four-dam study was conducted during the 2012 summer out-migration using 14,026 subyearling Chinook Salmon O. tshawytscha out-migrants with surgically implanted acoustic micro-transmitter tags. The release–recapture design consisted of 9 different release locations and 14 di...