Acoustic Transmitters Research Articles

Temporal and Spatial Relationships of Yellowfin Tuna to Deepwater Petroleum Platforms in the Northern Gulf of Mexico

AbstractIn 2006–2007, 110 Yellowfin Tuna Thunnus albacares were tagged with acoustic transmitters near deepwater oil platforms and one drillship in the northern Gulf of Mexico off the Mississippi River delta to determine the extent to which platforms act as fish aggregating devices (FADs). Vemco acoustic receivers were installed on six deepwater platforms to detect the presence of tagged individuals. Five of 12 Yellowfin Tuna captured in 2006 were detected in 2007, demonstrating multi‐year presence in the region. Ninety Yellowfin Tuna were detected in 2007, resulting in 221 platform residencies and 32 single detections. Duration of residence at a platform was positively correlated with the platform's depth, and the number of transitions decreased with platform‐to‐platform distance. In total, 109 movements between platforms by 46 (51%) different individuals were detected, traveling distances of up to 98.2 km. Yellowfin Tuna displayed interactions with deepwater platforms in the northern Gulf of Mexico similar to their interactions with FADs and other studied geological features, by way of aggregating or using them as meeting points, landmarks, and stopovers within a movement corridor. The large number of oil and gas platforms located in the northern Gulf of Mexico may have a significant effect on distribution, retention, and migration of Yellowfin Tuna populations in this area of the gulf.

Reef manta ray social dynamics depend on individual differences in behaviour

Knowledge of the drivers of fine-scale spatial ecology in wide-ranging marine species is vital to understand population structuring and conserve threatened species. Movements and habitat use are likely to be strongly influenced by social relationships between individuals, and social units within animal populations may be subject to distinct selective pressures. Here we used passive acoustic telemetry and network-based analyses to investigate the site visit patterns and social affiliations of reef manta rays, Mobula alfredi , in Raja Ampat, West Papua. Acoustic transmitters were externally deployed on 27 rays that were tracked for up to 110 days. Visit profiles were retrieved from nine acoustic receivers positioned in clusters at known aggregation sites, enabling analysis of movement behaviour and social processes at various spatial scales. We utilized Bayesian inference and a double permutation method to address issues in sampling and hypothesis testing on social networks constructed from automated telemetry data. We found that social affiliations were assorted into spatially defined communities which remained stable over several weeks to months, although many affiliations were short lived. Interindividual variability in detection profiles was correlated with social network metrics. Individuals with high levels of site attachment had stronger social affiliations, while individuals that regularly attended different receiver clusters were more central to the overall social network. These results suggest that reef manta ray movements, habitat preferences and social relationships should be understood as linked behavioural processes for which variability between individuals and groups may drive emergent population structure. Future research and local management of manta rays will likely benefit from identifying how, where and why social gatherings occur. • We used acoustic telemetry to record fine scale social dynamics in reef manta rays. • Social affiliations were assorted into spatial communities. • Social structuring persisted over time periods of weeks to months. • Individuals with high levels of area fidelity had stronger affiliations. • Mobile individuals were important in connecting social networks.

Movements of Hatchery-Reared Dusky Groupers Released in a Northeast Atlantic Coastal Marine Protected Area

No-take areas are key instruments to promote the effectiveness of Marine Protected Areas (MPAs), particularly concerning the protection of endangered species such as the dusky grouper (Epinephelus marginatus). However, despite the establishment of no-take areas and the prohibition of catching this species in a southwestern Portuguese MPA (SACVMP—‘Sudoeste Alentejano’ and ‘Costa Vicentina’ Marine Park) since 2011, there is still no evidence of population recovery. By using acoustic biotelemetry, this work aimed to evaluate the feasibility of restocking hatchery-reared adult dusky groupers in two no-take areas within the SACVMP. In 2019 and 2021, thirty groupers were tagged with acoustic transmitters and the site attachment and movements of the groupers were assessed in the releasing sites (no-take areas). None of the tagged fish settled down in either of the areas, leaving the no-take areas mainly at dusk and night. Some individuals displayed extended movements of more than a hundred kilometers along the Portuguese coast which was rarely reported for this species. At least in some coastal stretches, those movements were performed close to the shore, which may evidence the importance of coastal MPAs to protect and promote the connectivity of species more associated with rocky reef habitats. Following studies should focus on the conditions that promote site attachment and fidelity by hatchery-reared dusky groupers so that future large-scale restocking programs can be successful in MPAs with appropriate habitats.

Informative priors assess tradeoffs between mark–recapture and telemetry-based fish movement in a large river system

Telemetry and mark–recapture provide movement information, but each approach comes with tradeoffs, potentially producing conflicting understandings of fish movement patterns. Using a Bayesian framework that allows exchanging priors from either method may help assess these inconsistencies. We evaluated channel catfish Ictalurus punctatus movements in the Red River of the North and Lake Winnipeg system, which impacts harvest management across different jurisdictions and affects different ecosystems (e.g., lotic and lentic). Channel catfish were tagged with T-bar tags or acoustic transmitters. The resulting movement data were modeled using a Bayesian multi-state Cormack–Jolly–Seber model to estimate survival, movement, and recapture probabilities. Model estimates with uninformative priors showed a greater tendency of downstream movement from the Red River into Lake Winnipeg for the T-bar tags. In contrast, the telemetry method showed fish predominantly stay in the river. However, exchanging increasingly stronger prior information from the alternative method's model revealed that telemetry movement estimates were less sensitive than the T-bar model to informative priors. Using priors from both methods provided a transparent means to assessing tagging approach tradeoffs quantitatively.

Effects of tag type and surgery on migration of Atlantic salmon (Salmo salar) smolts.

Tagging salmon smolts to provide information about the timing of outmigration has been a common approach to monitor phenology and model the risk of encountering stressors. However, the validity of tagging has come under scrutiny because of the sensitivity of this parameter in various management systems. We studied the probability of migration, timing of migration and growth during migration for Atlantic salmon smolts tagged with three different tags in the River Dale, western Norway. Two groups were tagged with passive integrated transponder (PIT) tags via a small ventral nonsurgical incision, either a 12 mm or a new 16 mm PIT tag. Two groups were subjected to surgical implantation of either a dummy acoustic transmitter or a 12 mm PIT tag (a sham surgery). Overall, 71% of the tagged smolts were recaptured at the downstream Wolf trap. Smolts from the sham tagged group were recaptured most frequently (78%) compared to dummy acoustic transmitters and 16 mm PIT tags (both 68%), but the differences were not significant. Results agree with prior assessments that longer smolts migrated earlier, with about half a day earlier migration for each millimetre total length of the smolt, but did not suggest any difference in time of migration among the tag types. Growth in length was evident from release to recapture, with smaller smolts exhibiting greater growth and no effect of tagging treatment. Our findings suggest that inferences about the timing of outmigration for salmon smolts based on acoustic tagging should be made cautiously because of the relationship among tag size, suitable fish size and the timing of a tagged individual's migration.

Detection range of two acoustic transmitters in four reservoir habitat types using passive receivers

BackgroundRecently, South Dakota Department of Game, Fish, and Parks (SDGFP), has undertaken a suite of rigorous acoustic telemetry studies. The goals and scope of the individual research projects vary but all use the same receiver array throughout Lake Sharpe in central South Dakota. Prior to initiating the telemetry studies, we sought to describe the detection probability of receivers from a representation of habitats within Lake Sharpe, South Dakota. We used both a V9-2H transmitter and a V13-1L transmitter in combination with VR2W 69 kHz passive receivers [all from Innovasea (Vemco)] to determine detection probability in four novel habitats of Lake Sharpe. Both transmitter and receiver were moored at fixed distances (200 m 400, and 600 m) for multiple consecutive days and detection probability compared between transmitter type, distance, site, and diel period using ANOVA following arcsine square-root transformation.ResultsWe found significant differences in detection probability between the four habitat types for both the V9 and V13 transmitters. Sites protected from wind and wave action, and with little boat traffic, had larger detection ranges compared to areas that were wind exposed and host more boat traffic. The site immediately downstream from a hydroelectric dam that is exposed to both high wind fetch and is popular for boating, exhibited the poorest detection probability at all distances for both transmitter types. V13 transmitters consistently exhibited greater detection probability relative to V9 transmitters and this difference was greater at further distances. In general, detection probability was higher at nighttime compared to daytime and these differences were significant dependent on transmitter, site, and distance.ConclusionsUsing the information presented, SDGFP has modified their receiver array to maximize the ability to detect acoustic transmitters in the novel habitats of Lake Sharpe. Specifically, receiver spacing was reduced and/or expanded dependent on the distance, where 50% detection probability was attained. More work is needed to identify those factors that influence detection probability of acoustic telemetry systems.

Insights into Chinook salmon (Oncorhynchus tshawytscha) movement ecology in the terminal reaches of the upper Yukon River during the spawning migration

Chinook salmon ( Oncorhynchus tshawytscha (Walbaum, 1792)) from the upper Yukon River are highly unique, with some populations migrating nearly 3000 km to spawning habitat near the northern range limit for the species. We conducted a 4-year study to understand the behaviour of Chinook salmon in the terminal reaches of their migration by tagging salmon with acoustic and radio transmitters in Whitehorse, Yukon, Canada, ∼2800 km from the ocean. Various migration characteristics were quantified for Chinook salmon, including en route mortality, diel behaviour, migration rates, and homing patterns, and associations with salmon origin (wild vs. hatchery), sex, size, and migration timing were explored. Salmon had high survival to spawning grounds (>98%) and migrated throughout all hours of the day, with higher proportions of nighttime movements in a smaller spawning tributary than in the Yukon River mainstem. Migration rates were faster for larger salmon as well as late-arriving salmon, which was likely necessary to ensure they had sufficient time and suitable conditions on spawning grounds to reproduce. Non-direct homing movements (e.g., tributary exploration) were more common in male salmon and considerably increased migration distance through the study area. Findings from this study may help to inform the complex international and inter-nation management of these increasingly threatened Chinook salmon populations.

Residency and Use of an Important Nursery Habitat, Raja Ampat’s Wayag Lagoon, by Juvenile Reef Manta Rays (Mobula alfredi)

The behaviour and spatial use patterns of juvenile manta rays within their critical nursery habitats remain largely undocumented. Here, we report on the horizontal movements and residency of juvenile reef manta rays (Mobula alfredi) at a recently discovered nursery site in the Wayag lagoon, Raja Ampat, Indonesia. Using a multi-disciplinary approach, we provide further corroborative evidence that the lagoon serves as an important M. alfredi nursery. A total of 34 juvenile rays were photo-identified from 47 sightings in the sheltered nursery between 2013–2021. Five (14.7%) of these individuals were resighted for at least 486 days (~1.3 years), including two juveniles resighted after 641 and 649 days (~1.7 years), still using the nursery. Visually estimated (n=34) disc widths (DW) of juveniles using the nursery site ranged from 150–240 cm (mean ± SD: 199 ± 19), and the DW of two juveniles measured using drones were 218 and 219 cm. Five juveniles were tracked using GPS-enabled satellite transmitters for 12–69 days (mean ± SD: 37 ± 22) in 2015 and 2017, and nine juveniles were tracked using passive acoustic transmitters for 69–439 days (mean ± SD: 182 ± 109) from May 2019–September 2021. Satellite-tracked individuals exhibited restricted movements within Wayag lagoon. The minimum core activity space (50% Utilisation Distribution-UD) estimated for these five individuals ranged from 1.1–181.8 km2 and the extent of activity space (95% UD) between 5.3–1,195.4 km2 in area. All acoustically tagged individuals displayed high residency within the nursery area, with no acoustic detections recorded outside the lagoon in the broader Raja Ampat region. These juveniles were detected by receivers in the lagoon throughout the 24 h diel cycle, with more detections recorded at night and different patterns of spatial use of the lagoon between day and night. The observed long-term residency of juvenile M. alfredi provides further compelling evidence that the Wayag lagoon is an important nursery area for this globally vulnerable species. These important findings have been used to underpin the formulation of management strategies to specifically protect the Wayag lagoon, which will be instrumental for the survival and recovery of M. alfredi populations in Raja Ampat region.

Taking the time for range testing: an approach to account for temporal resolution in acoustic telemetry detection range assessments

BackgroundIn acoustic telemetry studies, detection range is usually evaluated as the relationship between the probability of detecting an individual transmission and the distance between the transmitter and receiver. When investigating animal presence, however, few detections will suffice to establish an animal’s presence within a certain time frame. In this study, we assess detection range and its impacting factors with a novel approach aimed towards studies making use of binary presence/absence metrics. The probability of determining presence of an acoustic transmitter within a certain time frame is calculated as the probability of detecting a set minimum number of transmissions within that time frame. We illustrate this method for hourly and daily time bins with an extensive empirical dataset of sentinel transmissions and detections in a receiver array in a Belgian offshore wind farm.ResultsThe accuracy and specificity of over 84% for both temporal resolutions showed the developed approach performs adequately. Using this approach, we found important differences in the predictive performance of distinct hypothetical range testing scenarios. Finally, our results demonstrated that the probability of determining presence over distance to a receiver did not solely depend on environmental and technical conditions, but would also relate to the temporal resolution of the analysis, the programmed transmitting interval and the movement behaviour of the tagged animal. The probability of determining presence differed distinctly from a single transmission’s detectability, with an increase of up to 266 m for the estimated distance at 50% detection probability (D50).ConclusionWhen few detections of multiple transmissions suffice to ascertain presence within a time bin, predicted range differs distinctly from the probability of detecting a single transmission within that time bin. We recommend the use of more rigorous range testing methodologies for acoustic telemetry applications where the assessment of detection range is an integral part of the study design, the data analysis and the interpretation of results.

Using Telemetry Sensors Mapping the Energetic Costs in European Sea Bass (Dicentrarchus labrax), as a Tool for Welfare Remote Monitoring in Aquaculture

Physiological real-time monitoring could help to prevent health and welfare issues in farmed fishes. Among physiological features that can be of interest for such purposes, there is the metabolic rate. Its measurement remains, however, difficult to be implemented in the field. Thus, mapping the fish acceleration recorded by tag with the oxygen consumption rate (MO2) could be promising to counter those limitations and to be used as a proxy for energy expenditure in the aquaculture environments. In this study, we investigated the swimming performance (Ucrit) and the swimming efficiency (Uopt, COTmin), and we estimated the metabolic traits (standard and maximum metabolic rates, SMR and MMR, as well the absolute aerobic scope, AS) of European sea bass (Dicentrarchus labrax; n = 90) in swimming tunnel. Among all tested fish, 40 fishes were implanted with an acoustic transmitter to correlate the acceleration recorded by the sensor with the MO2. In this study, the mean SMR, MMR, and AS values displayed by sea bass were 89.8, 579.2, and 489.4 mgO2 kg−1 h−1, respectively. The Uopt and COTmin estimated for sea bass were on average 1.94 km h−1 and 113.91 mgO2 kg−1 h−1, respectively. Overall, implantation of the sensor did not alter fish swimming performance or induced particular stress, able to increase MO2 or decrease swimming efficiency in tagged fish. Finally, acceleration recorded by tag has been successfully correlated with MO2 and fish mass using a sigmoid function (R2 = 0.88). Overall, such results would help for real-time monitoring of European sea bass health or welfare in the aquaculture environment in a framework of precision livestock farming.

Frequency-multiplied cylindrical triboelectric nanogenerator for harvesting low frequency wave energy to power ocean observation system

Cylindrical triboelectric nanogenerators (C-TENGs) have been designed for low frequency wave energy harvesting. However, the random, and low amplitude and frequency of the ocean waves represent a major challenge for the operation and performance of most C-TENGs. A C-TENG must be able to operate and be triggered by any wave conditions, even in the middle of the ocean, with uniform, low amplitude, and low frequency water waves. Here, a frequency-multiplied cylindrical TENG (FMC-TENG) that uses magnets to store potential energy and instantly release it to produce high frequency kinetic energy, was designed to increase the operating frequency of the TENG using low frequency, uniform water waves and increase the power generated. A semi-analytical modeling of the FMC-TENG was performed to theoretically verify its effectiveness. Then, the electrical characteristics of the FMC-TENG were evaluated by comparison with a conventional C-TENG in a wave motion simulator. The FMC-TENG was optimized in a 12 m long water tank, and its peak power density reached 6.67 W/m3 under a wave frequency of 0.33 Hz. Finally, an array of FMC-TENGs successfully powered an acoustic transmitter, demonstrating the ability to power an ocean observation system.

An implantable biomechanical energy harvester for animal monitoring devices

Insufficient service life and the resulting need for battery replacements have been a great challenge for implantable electronic devices. This is particularly true for animal tracking applications, because recapturing animals is often unlikely once they are released to the wild. To tackle this problem, we developed a biomechanical energy harvester that uses a Macro Fiber Composite™ (MFC) piezoelectric beam to harvest the mechanical energy from animals’ body bending movements as the power source for implantable and wearable devices. Prototypes of an underwater acoustic transmitter using this technology were subdermally implanted into juvenile white sturgeon and their energy harvesting performance was evaluated through the devices' transmissions. The fish successfully recovered from the implantation surgery and freely swam inside a tank. The transmitter prototypes in the fish continually transmitted signals for a period up to 5 weeks. A benchtop test setup was also created to emulate the fish’s body bending, estimate the device’s energy harvesting performance in the live fish, and perform accelerated fatigue testing of the energy harvester by applying test parameters learned from a video study of the fish’s body movement and behavior characteristics. The gradual depolarization of the piezoelectric ceramic material in the MFC under cyclic mechanical loading was the main limiting factor for the life span of the energy harvester. Pathways for improvement are proposed to achieve long-term efficacy of powering implantable and wearable electronic devices.

Coastal infrastructure alters behavior and increases predation mortality of threatened Puget Sound steelhead smolts

AbstractFundamental movements of migratory species can be substantially influenced by marine habitat disruptions caused by coastal infrastructure. The Hood Canal Bridge (HCB) spans the northern outlet of Hood Canal in the Salish Sea, extends 4.6 m (15 ft) underwater, and forms a partial barrier for steelhead migrating from Hood Canal to the Pacific Ocean. Spatial mark–recapture survival models using acoustic telemetry data indicate that only 49% (2017; 95% confidence interval (CI) = 40%–58%) and 56% (2018; 95% CI = 48%–65%) of the steelhead smolts encountering the HCB survived past the bridge and 7 km to the next array. We studied fine‐scale movements of more than 300 steelhead smolts to understand how migration behavior was affected across the entire length of the HCB and to quantify spatial and temporal patterns of mortality. Individually coded acoustic telemetry transmitters implanted in juvenile steelhead were used in conjunction with an extensive array of acoustic receivers surrounding the HCB to obtain approximations of the path each steelhead took as they encountered the bridge structure. Steelhead survival past the HCB appeared unaffected by tidal stage, population‐of‐origin, approach location, current velocity, or time of day, but was influenced by week of bridge encounter. Behavioral data from transmitters with temperature and depth sensors ingested by predators are consistent with high levels of marine mammal predation. This study confirms the considerable impact of the HCB on Endangered Species Act‐listed steelhead smolt survival, and provides detailed information on the behavior of steelhead smolts and their predators at the HCB for use in planning recovery actions.

Estimating Adult Pacific Salmon Energy Use in Coastal British Columbia and the Fraser River Estuary with Acoustic Accelerometer Transmitters

Estimating Adult Pacific Salmon Energy Use in Coastal British Columbia and the Fraser River Estuary with Acoustic Accelerometer Transmitters

Measurements of American lobster heart rate and movements in the wild using a low-cost open source datalogger

To better understand the behavior of the American lobster (Homarus americanus) in the wild, we developed the C-HAT (Crustacean Heart and Activity Tracker): a datalogger capable of continuously recording the triaxial acceleration, compass heading, and heart rate of lobsters that are freely moving in their natural habitat. C-HATs and acoustic transmitters were affixed to six lobsters that were released within an acoustic positioning array off the coast of New Hampshire (USA) and recaptured by divers after 15–47 h at large. Lobster heart rates tended to be ~ 60 beats per minute (bpm) at rest, but increased to ~ 80 bpm during periods of activity. The presence of brief cardiac startle responses during the beginning of some periods of activity suggested that at least a third of their movement bouts occurred in response to external stimuli, such as interactions with other species. The combination of acoustic positioning data and datalogging allowed us to determine if various indices of acceleration could be used to estimate distance traveled. We found a significant correlation between a Movement Index (MI), based on differentiation of the three axes of acceleration, and the distance lobsters traveled in 10 min based on telemetry data. This enabled us to use the MI in concert with compass headings to reconstruct lobster movement paths via dead reckoning. This study demonstrates the potential for low-cost, open-source, dataloggers to provide detailed information on the daily behavior and physiology of marine invertebrates in the wild.

Passage efficiency and behaviour of sea lampreys (Petromyzon marinus, Linnaeus 1758) at a large marine–freshwater barrier

AbstractPassage success of sea lampreys Petromyzon marinus and behaviour in the vicinity of man‐made structures such as marine–freshwater barriers are poorly understood. To mitigate these migratory problems, a better understanding of passage behaviour is needed. To investigate this, 25 sea lampreys were tagged with V7 VEMCO acoustic transmitters at a large marine‐freshwater barrier, consisting of ten sluice gates and a ship lock complex in the Netherlands. Overall passage success was assessed to be 16%, with four sea lampreys passing the sluice gates, while none passed the ship locks. Successful passage through the barrier occurred either at the beginning or at the end of a discharge period, when water level differences between sea and lake and thus water velocities were relatively low. Most sea lamprey showed exploratory searching behaviour but only for a short duration, before leaving the area again when unsuccessful. Low passage success and search duration were likely related to the unnatural infrequent occurrence of flow and only short lasting windows with suitable conditions for passage at the sluice gates. To mitigate the poor migration success of sea lampreys at the marine‐freshwater barrier with the current adapted sluice management, a fish passage facility with lower water velocities and longer or continuous passage opportunities is needed.

Internal seiches as drivers of fish depth use in lakes

AbstractInland temperate lakes undergo various physical processes, such as thermal stratification, that dictate the spatial availability of suitable temperature and dissolved oxygen conditions. Here, we use intensive limnological monitoring and acoustic telemetry transmitters implanted in wild fish to document the magnitude and frequency of thermocline deflection events (i.e., wind driven internal seiches that lead to upwelling of hypoxic hypolimnetic water) and their influence on freshwater fish depth use in a coastal embayment of Lake Ontario. The embayment experienced around 100 internal seiche events during a 3‐month period and tracking of walleye (Stizostedion vitreus) vertical positions in the water column showed clear trends of avoidance of low dissolved oxygen. Quantile regression showed a significant correlation between walleye vertical position and the depth of the 3, 4, and 5 mg L−1 oxyclines, with the 3 mg L−1 oxycline having the largest effect. Upwellings of the hypoxic hypolimnion forced walleye to use the water column above these fluctuating oxyclines (5th percentile, p < 0.001), with 94.2% of detections occurring at depths above the 3 mg L−1 oxycline. Understanding how fish respond to upwelling events (both temperature and oxygen) is important for fisheries assessment, management, and habitat restoration planning as there is clear avoidance of suboptimal oxygen conditions and sampling in the overcrowded fringes of these low‐oxygen zones could artificially inflate population estimates.

The effect of externally attached archival data loggers on the short-term dispersal behaviour and migration speed of European eel (Anguilla anguilla L.)

BackgroundExternally attached archival data logging tags are increasingly used to unravel migration routes of fish species at sea. Due to the relatively large size of the tags, their application on seaward migrating anguillid eels often forms a challenge in terms of feasibility and impact on the eel’s swimming performance. In this study, we investigated the impact of externally attached pop-up data storage tags (PDSTs) on the departure direction, time spent at the release location and ground speed of European eels (Anguilla anguilla).ResultsWe tagged 66 eels with internal acoustic transmitters of which half of the eels were additionally tagged with externally attached PDSTs. A network of acoustic receivers allowed us to analyse if the dispersal behaviour (i.e. residence time and departure direction) from the release site differed between eels tagged with and without the PDSTs. In addition, we tracked the eels for ca. 83 km in the marine environment and determined their migration speed. The results showed no differences between eels tagged with or without external PDSTs in respect of the external tagging effect on residence time (n = 60), departure direction at the release site (n = 60) or on the migration speed (n = 20).ConclusionsWe conclude that the impact of the PDSTs is minimal on these metrics for at least the first part of the marine migration. While these field-based findings suggest that anguillid eels may be largely unaffected by the applied PDSTs, we recognize that more research is needed in both the field and the laboratory to study the impact of PDSTs and externally attached tags in general on fish swimming performance and energy expenditure. This can help interpret the results from the field, but also aid developing more hydrodynamic tag shapes or improved attachment methods.

Acoustic telemetry data on lake-migratory brown trout, Salmo trutta lacustris L., behavior in Lake Hańcza, northeastern Poland, within one year of release

Abstract The poor results of lake-migratory brown trout, Salmo trutta lacustris L., restoration in Lake Hańcza Nature Reserve prompted undertaking the current study that sought to verify if hatchery-reared fish age 2+ can survive the critical period of acclimation and remain in the lake. Thirty-one individuals were tagged with coded acoustic transmitters and observed for 317 days. This method helped to analyze: 1) the spatial behavior of tagged fish for one year following their release; 2) the possible differences in the behavior of fish released in various places habitually used for stocking. By the end of study, 6.5–12.9% of the tagged fish remained in the lake. The most interesting phenomenon the data indicated was the trout behavior in late spring and early summer, when the fish moved vigorously along the longitudinal axis of the lake continuously for several weeks. The reasons for the fish movements observed in Lake Hańcza were not clear. For this unique species/population it is important to determine whether such behavior is typical of this fish also in other water bodies and if it is only seen in hatchery-reared fish aged 2+ and 3+.

Influence of dense macrophyte vegetation and total gas saturation on the performance of acoustic telemetry

BackgroundAcoustic telemetry is widely used as a method for high resolution monitoring of aquatic animal movement to investigate relationships between individual animals and their environment. In shallow freshwater ecosystem, aquatic macrophytes are common and their presence increases habitat complexity and baffles sound propagation. These properties may be likely to affect the performance of acoustic telemetry, however, to date this issue has received little attention, when studying the ecology of movements of fishes in and around the important macrophyte habitats. Here, we conducted a range-test study in a freshwater riverine ecosystem, with mass development of the aquatic macrophyte Juncus bulbosus (L.), to assess how dense macrophytes impact detection probability, detection range, and performance of a three-dimensional receiver positioning system. Supersaturation of gas frequently occurs at the study site as a by-product of upstream hydroelectric power generation and gave a unique opportunity to investigate how total gas saturation affects the performance of acoustic telemetry. We also investigated the influence of environmental conditions (i.e., day-of-year, time of day, average water level above J. bulbosus) on detection probability together with vertical position of transmitters and location inside or outside macrophytes.ResultsThe detection probability and range were generally low for transmitters in and outside J. bulbosus stands, with mean hourly detection probabilities ranging from 1.18 to 5% and detection ranges between 17.26 m ± 0.74. The interaction between total macrophyte biomass and distance to receiver reduced the detection probability and detection range substantially. Detection probability further decreased with increasing total gas saturation, and transmitters positioned near the sediment and close to the surface also had lower detection probabilities compared to receivers in the middle of the water column. Finally, the low detection probability affected position estimates, where only 23% of the detections could be positioned using the average positioning estimation method and positional accuracy and precision were low ranging from 1.48 to 164.8 m and 0 to 50.1 m, respectively.ConclusionsOur findings demonstrate the impact of macrophytes and total gas saturation on detection probability and range of acoustic transmitters in a shallow ecosystem, where tagged fish are unlikely to be detected by receivers or positioned. These results emphasise that in situ range testing is strongly needed before determining the density and design of receiver array when performing acoustic telemetry studies in shallow ecosystems.