Passive Telemetry Research Articles

A novel process to infer the reliability of ecological information derived from passive acoustic telemetry track reconstruction

Abstract Passive acoustic telemetry can be used within cooperative networks to track migratory species over great distances at a relatively low cost. However, the non‐uniform distribution of fixed receivers within networks often results in sporadic detection data. Here, we propose a novel combination of methods to measure the reliability of hot spot analysis results derived from track reconstructions of passive telemetry data. We use an iterative process to simulate tracks of animals, derive detection data from these tracks, and reconstruct tracks from these derived data using a movement model. We then compare quadrat count residuals from the simulated and reconstructed tracks for different grid resolutions. The methodological framework is outlined in detail and tested on the acoustic telemetry cooperative arrays off the US East Coast. Our methods are applied to a subset of blacktip shark, Carcharhinus limbatus, acoustic telemetry detection data collected off the US East Coast. We then apply the resultant quadrat count to a hot spot analysis to determine the distribution of animals derived from these track reconstruction methods. We integrate the results of our methods process with the hot spot analysis results to determine the reliability of this distribution information. The track reconstruction methods performed well in coastal regions, from Palm Beach County, FL to Long Island, NY, minimized the clustering effect of high densities of receivers, and closed the gaps in some regions that were lacking receiver coverage. This performance was primarily affected by the presence/absence of receivers, and to a lesser extent by receiver density and water depth, depending on the grid resolution. Our method combination demonstrates a means by which passive telemetry data can be regularized to determine the spatial distribution of animals across regions with non‐uniform sampling coverage. These methods also allow the user to determine the reliability of animal distribution products in a telemetry array and the factors that contribute to high accuracy and precision. Our iterative process enables managers to infer the reliability of ecological results in decision‐making processes and could be leveraged for use as a gap analysis to develop a national strategy for telemetry assets.

Spatial ecology and thermal preferences of muskellunge within a Midwest impoundment

AbstractMuskellunge are a valuable sportfish species which has been stocked throughout North America. Stocking is a strategy to generate angling opportunities by introducing species to waterbodies that otherwise would not have contained the fish, such as impoundments and reservoirs. Therefore, understanding the ways fish interact with different waterbodies is critical for managers to understand. To that end, we utilized a year‐long passive telemetry study with muskellunge in a reservoir known for its muskellunge angling. Additionally, we employed temperature loggers to track lake temperatures. We found that smaller female muskellunge were more resident at sites compared to similar‐sized males, although fish did not exhibit site‐specific preferences. We also found that fish moved high distances over the course of the year without time‐specific differences. Furthermore, we found evidence that muskellunge was selected for thermal refuges in the reservoir; however, in summer, when water temperatures were elevated, fish inhabited water, which has been shown to increase incidental mortality. The results of this study indicate a need for muskellunge managers, especially in reservoirs, to consider water temperature in angling regulations. Additionally, our results highlight a need for adding habitat structure in reservoirs and altering stocking densities of fish. Collectively, these results will help inform managers on muskellunge spatial interactions within a reservoir and achieve management goals.

Dynamic transient response measurement method for parity-time-symmetric LC telemetry sensors

Parity-time symmetry concept has been utilized to develop high precision LC passive wireless sensors. However, they often use the traditional frequency sweeping method for measurements, thus the measurement precision and speed are strongly influenced by the performance of the frequency domain analysis instrument. To solve this issue, herein we proposed a time domain measurement method and extracted sensing information from the transient response signals of the reader. Its measurement speed was much faster than that using the frequency domain analysis instrument. A distance sensing system was developed to demonstrate the feasibility of the new method. It showed a resolution of less than 300 nm for detections of centimeter range, and the measurement time was as short as 100 μs, which was at least 1000 times faster than that using the traditional method. This technology can be explored as an innovative strategy for LC passive telemetry sensing.

Movement of Paddlefish once past a lock‐and‐dam structure on the Alabama River

AbstractObjectiveMovement of fish past dams can be facilitated by dedicated fish passage structures, navigational locks, and crested spillways, with the efficacy of a passage structure depending strongly on the nature of the system (height of the dam, flow rate, etc.) and the fish's behavior and swimming capability. However, once the fish have passed a dam, whether by using a mitigation structure or due to active translocation, they encounter a different habitat upstream versus in the tailrace, potentially affecting their ability to continue their upstream migration.MethodsHere, we had two objectives. First, we determined whether Paddlefish Polyodon spathula that successfully passed a structure continued their upstream migration in the Alabama River. Because assuring passage by tagged fish required that we move the fish past the dam, our second objective was to determine whether translocated fish exhibited fallback behavior (downstream drift or movement postrelease that would compromise their continued migration). We used both active and passive telemetry methods to quantify the postpassage movements of tagged and translocated Paddlefish.ResultFish that were translocated above Claiborne Lock and Dam (CLD) exhibited upriver movements once translocated, and they exhibited no fallback (i.e., downstream movement with delayed or no continuation upstream). Timing of movement relative to spawning periods did not influence initial fish movement or the likelihood of reaching the next upstream dam (Millers Ferry Lock and Dam [MFLD]; ~100 river kilometers upstream) within the first 30 days of observation, but more fish that were tagged and released during the early prespawn period made it to within 4.83 km of MFLD (the location of our closest receiver below MFLD) relative to fish from the prespawn or spawning period. Fish that were released above CLD had a lower probability of being subsequently detected downstream of their release sites compared to fish that were released below CLD.ConclusionOur findings support that Paddlefish will continue their upstream migration once they have passed a structure, despite changes in habitat.

Flock: Accurate Network Fault Localization at Scale

Inferring the root cause of failures among thousands of components in a data center network is challenging, especially for "gray" failures that are not reported directly by switches. Faults can be localized through end-to-end measurements, but past localization schemes are either too slow for large-scale networks or sacrifice accuracy. We describe Flock, a network fault localization algorithm and system that achieves both high accuracy and speed at datacenter scale. Flock uses a probabilistic graphical model (PGM) to achieve high accuracy, coupled with new techniques to dramatically accelerate inference in discrete-valued Bayesian PGMs. Large-scale simulations and experiments in a hardware testbed show Flock speeds up inference by >10000x compared to past PGM methods, and improves accuracy over the best previous datacenter fault localization approaches, reducing inference error by 1.19-11x on the same input telemetry, and by 1.2-55x after incorporating passive telemetry. We also prove Flock's inference is optimal in restricted settings.

Miniaturized Fully Passive Wireless Neural Recording With Heterogeneous Integration in Thin Packages

Wireless fully-passive neural recording systems are demonstrated with heterogeneous integration of sensing, mixing, and communication components in flexible polymer dielectric films. The recording neurosensor has an antenna, antiparallel diode, and a by-pass capacitor to modulate an incoming carrier signal with the neuropotentials and backscatter the mixed signal to an external reader circuit. Planar antennas are realized on Liquid Crystal Polymer (LCP) flexible substrates with low dielectric constant. The designed antenna topology is realized with a single metal layer and eliminates the dependency on substrate thickness, and leads to thinner sensors. This is a major advance compared to prior passive neural recording with rigid and thicker substrates and components. Approximately 80% thickness reduction and 20% volume reduction are achieved with a similar performance when compared to earlier studies. Our approach thus leads to low-cost and disposable wireless neurosensors on a flexible platform with heterogeneous integration. This paper thus advances innovative wireless neural recording in three aspects: a)advanced packaging for miniaturized neural recording with passive telemetry, through which the overall size of the sensor is reduced without degrading the performance. b) new antenna topologies for neural recording applications, and c) detailed power link analysis to estimate the minimum signal sensitivity.

What's the effectiveness of stocking actions in small creeks? The role of water discharge behind hatchery trout downstream movement.

Fish stocking to enhance freshwater fisheries or to improve the conservation status of endangered fish species is a common practice in many countries. Little is known, however, of the effectiveness of these practices in spite of the high efforts and investments required. The movement of subadult/adult hatchery-released brown trout Salmo trutta L. was studied by passive telemetry in a small tributary of Lake Lugano (i.e., Laveggio Creek, Canton Ticino, Switzerland). Hatchery fish, together with some resident wild individuals sampled during electrofishing surveys, were tagged with Passive Integrated Transponders (PIT) tags. Hatchery fish were released upstream and downstream a submersible monitoring antenna, which was anchored to the streambed in a pass-over orientation. The number of hatchery fish detected daily by the antenna (divided between fish released upstream and downstream the antenna) was analyzed in relation to the daily water discharge, to search for similar patterns in their fluctuation over time. Only the movement of fish released upstream the antenna displayed a significant relationship with water discharge, with the highest number of fish detected during periods of high-water flow, occurring after heavy rains. High-water discharge events had a significant role in hatchery trout downstream movement in our study site, likely acting as a driver for the downstream migration to Lake Lugano. Such events contributed to the poor effectiveness of stocking actions in this small tributary, providing further evidence against stocking strategies based on subadult/adult fish.

Behaviour affects capture probability by active sampling gear in a cyprinid fish

Animal behaviour interacts with various relationships within biota, and its variation among individuals may cause bias in behavioural research because of its impact on sampling efficiency. In this study, we simultaneously recorded fish behaviour during the reproductive season by passive telemetry and sampled a fish population using an active sampling method by boat electrofishing. A total of 1479 individuals of the cyprinid fish asp (Leuciscus aspius) were tagged, and their reproductive behaviour was recorded using passive telemetry systems in 2015–2020. We investigated whether capture probability was related to fish behaviour during reproduction (length of spawning, number of individual visits to spawning grounds, proportion of time spawning, arrival date and average daily arrival time). Overall, males were more likely to be captured than females (30 ± 4% standard error (SE) vs. 20 ± 3% SE probability) when present in the area. Traits favouring the odds of being captured differed between sexes and included the length of presence, proportion of time invested in spawning and average daily arrival time in males; in females, the capture probability was related to the length of presence and arrival date. This study suggests that even a large sample obtained using active gear may not represent the entire population’s behaviour because of behavioural-related bias in a population.

Does Fish Conditioning in Aquaculture Increase Survival Success in the Wild? A Case Study on a Cyprinid Fish

Many endangered fish species in the wild are artificially bred, and their populations are strengthened by the stocking of aquaculture-raised juveniles. Because fish from aquaculture are generally not well prepared for the challenging life in the wild, we tested whether training for selected challenges could improve fish survival after stocking. We chose conditioning on predation pressure (by learning predator image of northern pike Esox lucius using predator chemical cues and visual stimuli), increased rearing water velocity 20 cm × s−1, and direct exposure to predation. The juvenile cyprinid fish asp (Leuciscus aspius) was used as a model prey species. A total of 7949 asp were reared in four groups using a combination of high flow, predation, and control treatments (low flow, no predation; 2018, 2149, 1929, and 1856 individuals, respectively). Of these, 1800 individuals were released into three ponds with pike, and their mortality rates were monitored in relation to predation for two months after stocking using passive telemetry arrays. The remaining 6149 aquaculture-reared individuals were released directly into a large reservoir, while 1426 individuals that survived pike predation for two months were released after the pond experiment ended. Fish survival in a reservoir was monitored in 2020 and 2021 by boat electrofishing and passive telemetry. The effect of training in aquaculture was not detected in pond conditions, but the fish that survived direct predation from pike for two months in the semi-natural treatment were more likely to survive in the wild than their aquaculture-reared counterparts. In the laboratory environment, asp responded to predator chemical cues with an increase in shoal cohesion and swimming activity, which demonstrate their ability to detect chemical cues. However, exposure to more fluvial conditions did not result in increased critical swimming speed. The study suggests that conditioning tested in aquaculture may not be sufficient to prepare fish for the wild, while exposing fish to direct predation could increase fish survival.

A Sawtooth MEMS Capacitive Strain Sensor for Passive Telemetry in Bearings

The development of economical and high-sensitive strain sensor is crucial for precise measurement of strain in industrial applications, such as bearings. During operation, bearing itself is a harsh environment, which usually has large temperature variations and large centrifugal forces. This paper presents a sawtooth MEMS capacitive strain sensor for passive telemetry in bearings. The interdigital fingers are designed into sawtooth shape to decrease the influence of centrifugal acceleration. The strain sensor chip is 4mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times4$ </tex-math></inline-formula> mm in size, and is fabricated by a simple SOI process. Connecting the sensitive capacitor with an inductor, an LC resonant tank is formed, and the strain signal can be read out wirelessly and passively through a readout coil. Measurement results show that, in the range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0\sim 1000~\mu \varepsilon $ </tex-math></inline-formula> , the sensitivity of the LC strain sensor reaches 34kHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> , and the gauge factor (GF) of the strain sensor reaches 430. The influence of thickness of adhesive layer on the strain sensitivity is investigated. When the thickness of the adhesive layer reaches <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500~\mu \text{m}$ </tex-math></inline-formula> , the applied stress cannot be transferred at all. Finally, the LC strain sensor is tested on a rotating platform. The measured resonant frequency shows only 0.4% deviation under 1000m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> centrifugal acceleration.

Hydropeaking causes spatial shifts in a reproducing rheophilic fish

The hydropeaking regime below hydropower facilities represents a serious threat to riverine fauna and may cause declines in populations living under its influence. However, the knowledge on direct fish responses to the threat of hydropeaking is limited. Here, we aimed to test whether the hydropeaking generated 12 km upstream may have a negative effect on the position of actively spawning rheophilic fish, asp, Leuciscus aspius. Two passive telemetry antenna arrays were used to record fish position on the spawning ground. We monitored the position of spawning fish (545, 764 and 852 individuals) in three one-month long spawning seasons in 2017–2019 and related the changes in detection probability on the two antenna arrays to flow conditions, temperature, time of a day and individual fish ID. The fish detection on the spawning ground was negatively affected by the flow change (both increase and decrease) in time. Moreover, the probability of fish detection was also influenced by water temperature, the time of the day and, as seen from the magnitude of individual random effect variability, the detection probability was rather individual-specific. Hydropeaking resulted in the change of spawning behaviour and likely caused interruption of spawning or shifting spawning outside the optimal area for egg development. We therefore advise to reduce the hydropeaking regime during the rheophilic fish spawning season under fisheries or conservation interests.

Residency of bull sharks, Carcharhinus leucas (Carcharhiniformes: Carcharhinidae), at San Pedrillo Islet in Islas Murciélago, North Pacific of Costa Rica

Introduction: The bull shark, Carcharhinus leucas, is particularly vulnerable to anthropogenic actions because of its permanence in coastal ecosystems; populations depletion is registered in different places around the world. Aggregations of bull sharks have been reported in the North Pacific of Costa Rica, at Islas Murciélago, within the Guanacaste Conservation Area.&#x0D; Objective: To study the residency of bull sharks at San Pedrillo islet, Islas Murciélago.&#x0D; Methods: During the study period (June 2013 to February 2015) we used passive telemetry to tag 10 bull sharks.&#x0D; Results: All the sharks tagged were females, they were detected on 59 798 occasions by the acoustic receiver deployed in San Pedrillo. Acoustic signals from tagged sharks were received for a total period of 1 to 229 days (mean = 73.9 ± 71.3 days), with the last detections occurring on 9 January 2015. The Residency Index for each tagged shark across the entire monitoring period ranged from 0.41 to 1.00. The bull shark activity showed a significant pattern throughout the day at the receiver that specifically corresponded with the daily light cycle.&#x0D; Conclusions: This study concludes that San Pedrillo is an aggregation site (cleaning station) for bull sharks (C. leucas), possibly related to reproduction and not feeding behaviors.

Climbing up the ladder: male reproductive behaviour changes with age in a long-lived fish

High reproductive performance is the key attribute of male fitness, especially due to the high reproductive skew among the males of most animal species. Males of long-lived iteroparous species have opportunities to improve upon their previous reproductive attempts with increasing age. We collected individual-specific reproductive behaviour and age data on a cyprinid fish, the asp (Leuciscus aspius), from 2015 to 2019. We tested whether males changed their performance over time using a unique dataset where individual performance was recorded yearly with passive telemetry. Individual fish behaviour was tracked from one to five reproductive seasons at least a year after the tagging. Fish were scored by measures of quality (first arrival time, number of visits and time spent in the reproductive grounds, and encountered proportion of males to all adult fish). In general, fish improved in the first three metrics with age, suggesting a shift towards behaviours likely to enhance reproductive success as individuals aged. A larger size at tagging was predictive of earlier fish arrival on the spawning ground in subsequent years. Our study therefore demonstrates the importance of age as a factor when considering the potential reproductive success of long-lived fish species.Significance statementHigh reproductive performance is the key attribute of male fitness. Males of long-lived species reproducing multiple times in their life have opportunities to improve upon their previous reproductive performance with increasing age. In this 5-year study, we tracked a large cyprinid fish with telemetry systems during their reproduction. We investigated the age-related behavioural changes in males and demonstrated the improvement of male reproductive timing and length of stay with potential repercussions for male’s reproductive output. We emphasize the importance of old and experienced individuals among the fish population, which are often targeted and selectively removed from the human-managed waters.

Passive In-Band Network Telemetry Systems: The Potential of Programmable Data Plane on Network-Wide Telemetry

In the last few years, the emergence of Programmable Data Planes and the appearance of programming protocol-independent languages such as P4 have offered powerful tools to define new network protocols, as well as to redesign existing network applications and systems. Network telemetry is one of the main areas of interest identified by the P4 Application Working Group. The collection of network-wide, fine-grained network information in real-time is a critical requirement for the design of useful and adequate monitoring tools that can be integrated into complex Operations, Administration & Maintenance applications. Recent research has focused on the definition and implementation of in-band monitoring systems, where specifically dedicated monitoring packets are not required. Even though the In-Band Network Telemetry specification proposed by the P4 Language Consortium is the starting point of many of the in-band monitoring systems, this is not the only alternative. Therefore, in this work, we will describe and compare other P4-based in-band passive telemetry proposals.

Combining disciplines: Dealing with observed and cryptic animal residencies in passive telemetry data by applying econometric decision-making models

Migratory species do not necessarily behave migratory continuously. An important aspect of studying migratory species is therefore to distinguish between movement and resident behavior. Telemetry is a rapidly evolving technique to study animal movement, but the number of data processing techniques to account for resident behavior remains limited. In this study we describe how models that were initially developed to predict human customer behavior, i.e. two-part and three-part models, provide new insights in the movement of migrating eel by accounting for resident behavior apparent from telemetry data sets. In econometrics, two-part models take into account that the decision of a customer to purchase an item and the decision of the customer on the purchase quantity of the concerning product, might be affected by different factors. Similarly, the factors that affect the decision of a fish to migrate or to stay resident might be different from the factors that affect the swimming speed of the fish. Telemetry data of eel movement in the Permanent Belgian Acoustic Receiver Network (PBARN) of the Scheldt Estuary was used. This network with high detection probabilities allowed residencies to be recognized, defined, and introduced as zero values in a movement-residency data set. Two-part models, which consider movement decision, i.e. residency or movement, and movement intensity, i.e. swimming speed, as two different processes or parts of one larger model, outperformed one-part models that do not make that distinction. This underlines the complex migration behavior eels exhibit. These two-part models in turn were outperformed by three-part models that also accounted for cryptic (i.e. unobserved) residencies. While the one-part model identified the tides and the distance from the most upstream gate as most important for movement, the three-part models identified the tides as most important for the movement decision and the distance from the most upstream gate as most important for the movement intensity. Considering movement decisions, cryptic residencies and movement intensity in modeling efforts increased model performance by 9.8%, underlining the importance of acknowledging the potentially complex behavior animals exhibit.

Maladaptive migration behaviour in hybrids links to predator-mediated ecological selection.

Different migratory species have evolved distinct migratory characteristics that improve fitness in their particular ecological niches. However, when such species hybridize, migratory traits from parental species can combine maladaptively and cause hybrids to fall between parental fitness peaks, with potential consequences for hybrid viability and species integrity.Here, we take advantage of a natural cross‐breeding incident to study migratory behaviour in naturally occurring hybrids as well as in their parental species and explore links between migratory traits and predation risk.To achieve this, we used electronic tags and passive telemetry to record detailed individual migration patterns (timing and number of migratory trips) in two common freshwater fish species, roach Rutilus rutilus, common bream Abramis brama as well as their hybrids. Next, we scanned for tags regurgitated by a key avian predator (great cormorant Phalacrocorax carbo) at nearby roosting sites, allowing us to directly link migratory behaviour to predation risk in the wild.We found that hybrid individuals showed a higher number of short, multi‐trip movements between lake and stream habitats as compared to both parental species. The mean date of first lake departure differed between bream and roach by more than 10 days, while hybrids departed in two distinct peaks that overlapped with the parental species' averages. Moreover, the probability of cormorant predation increased with multi‐trip movement frequency across species and was higher for hybrids.Our data provide novel insights into hybrid viability, with links to predator‐mediated ecological selection. Increased exposure to predators via maladaptive migratory behaviour reduces hybrid survival and can thereby reinforce species integrity.

Quantifying and reducing epistemic uncertainty of passive acoustic telemetry data from longitudinal aquatic systems

Passive acoustic telemetry data are used to study animal movement in aquatic environments, but tools to process the data are limited. In areas that are too large to be fully covered by the limited detection ranges of receivers or acoustic listening stations, researchers generally assume that animals are residing in an area when they are detected frequently at specific receivers. There is, however, no consensus on how this area and frequency should be spatially and temporally defined respectively, thereby introducing some unaccounted uncertainty of this residency-at-receivers. In longitudinal aquatic systems such as rivers or estuaries, strategically placed receivers are often used as gates or curtains through which tagged animals have to pass. Rather than being a proxy for the time spent near receivers, the detections can serve as boundary conditions to delineate the durations that animals spent between receivers (i.e. residency-between-receivers). As such, providing a spatial and temporal context to the detections and enabling the quantification of epistemic uncertainty. To assess the usefulness of this approach, we analyzed telemetry data for migrating eel in a longitudinal estuarine acoustic tracking network of 21 gates. Results revealed a logarithmic relationship between epistemic uncertainty and gate network resolution, which indicates that transferring information from the spatial to the temporal level has a positive effect on the epistemic uncertainty. The poor correlation between the at-receivers and the between-receivers approach indicates that the latter, although less precise, may be more accurate. It should be noted that the suggested approach assumes that the gates of receivers are perfect detectors. If tagged animals are able to pass these gates undetected the uncertainty will actually be higher than assumed. Our approach is therefore less suited for large open areas such as lagoons or seas where gates with high detection probabilities are logistically challenging. This approach allows the quantification and reduction of epistemic uncertainty by providing a spatiotemporal context to the detections. Since establishing and maintaining passive telemetry networks is generally expensive and the results these networks generate are often used in decision making, an assessment of the network quality and data uncertainty is vital.

Home range of newborn blacktip reef sharks (Carcharhinus melanopterus), as estimated using mark-recapture and acoustic telemetry

Sharks play important functional roles in coral reef ecosystems. Studying reef shark populations’ spatial ecology also contributes important data for effective conservation planning. The purpose of this study was to define the home range of neonatal blacktip reef sharks (Carcharhinus melanopterus) around Moorea, French Polynesia, and compare estimates using both mark-recapture surveys and active acoustic telemetry. Mark-recapture surveys produced a minimum convex polygon (MCP) of 0.07 km2 that was significantly larger than the MCP derived from acoustic telemetry (0.02 km2). Acoustic telemetry produced 50 and 95% kernel utilization densities that were smaller (0.02 km2) and larger (0.14 km2) than home range estimates from mark-recapture surveys, respectively. Home range estimates from this study are the smallest that have been documented for neonatal blacktip reef sharks, possibly owing to the study sites’ proximity to deep channels. Mark-recapture and active acoustic telemetry are complementary approaches worthy of consideration where passive telemetry is impractical.

Negative feedback concept in tagging: Ghost tags imperil the long-term monitoring of fishes.

Wildlife monitoring using passive telemetry has become a robust method for investigating animal migration. With increased use, this method progressively pollutes the environment with technological waste represented by so called ghost tags (PIT tags ending in the environment due to reproductive expulsions, shedding or animal mortality). However, their presence in the environment may lead to failed detections of living individuals. We used tagging data from studies of the asp Leuciscus aspius and the bleak Alburnus alburnus collected from 2014 to 2018 and located ghost tag positions on the monitored spawning site using portable backpack reader for their detection. We modelled virtual river-wide flat-bed antennas (widths 0.2, 0.4, 0.6 and 0.8 m) representing monitoring effort and estimated the probability of the presence of ghost tags within the antenna field. Of 3724 PIT tags used in the study, we detected on the spawning ground 173 ghost tags originating from long-term monitoring. The ghost tags accumulated in the environment in time, suggesting insufficient degradation rate or shift downstream from the research site. Number of ghost tags present on the spawning ground led to high probability of disabled readings of tagged fish passing through the antenna electro-magnetic field. We demonstrate how accumulated ghost tags may cause detection failures for focal species and incomplete data acquisition. We infer that intensive long-term monitoring using PIT tag technology may encumber future data acquisition or entail additional costs for clean-up.

Testing the applicability of tagging the Great crested newt (Triturus cristatus) using passive integrated transponders

Tracking individual animals with small-sized passive integrated transponder tags (PIT tags) has become a popular and widespread method, one which can be used for investigating life history traits, including dispersal patterns of small protected animals such as newts. In this study, we tested the applicability of PIT tag usage for individual marking with the Great crested newt (Triturus cristatus) as a model amphibian species, and to test the detection of the newts in nature using a passive telemetry system. Clove oil was used as an anaesthetic before surgery. We implanted PIT tags under the skin of 140 newts. The survival rate of newts was 98.57%. X-ray images were taken to check the exact positions of the PIT tags. Since approximately 15.71% of the newts were capable of expelling the tag from their bodies, tag loss has to be accounted for in future behavioural studies dealing with newts and other amphibians potentially capable of frequent tag expulsion. Lastly, we detected by passive telemetry 97 individuals out of 100 released into a natural breeding pond. Males had higher activity (13 detected males vs 7 females per hour) than females, thus males could be detected if present with more certainty. The result of the movement behaviour showed that e.g. the male of T. cristatus in a breeding pond can travel up to 20 m in 78 seconds. In summary, this promising method could allow the automatic data collection of marked newts in aquatic as well as in terrestrial biotopes, providing data on their dispersal, diurnal activity and movement behaviour.