ArticlePDF Available

Abstract and Figures

Background Recent improvements in fixed acoustic monitoring receivers allow the tracking of individual aquatic animals over long periods of time with regular fine-scale positions. The VEMCO Positioning System (VPS) is now widely used, but various methodological issues remain to be clarified. The aim of this study was to analyze the spatial distribution of the probability of location and the positioning error over the entire surface of a hydropower reservoir, prior to analyzing fish behavior. Findings: Filtering the data set by the horizontal position error (HPE) significantly reduced the positioning error. Retaining only the positions with an HPE less than 15 retained 79% of VPS positions and decreased the positioning error by 33% (mean = 3.3 m, SD = 3.3 m). A higher probability of location was observed inside than outside the receiver array (44% and 36%, respectively). Moreover, the positioning error significantly differed inside (n = 243, mean = 2.4 m, SD = 2.1 m) and outside (n = 253, mean = 4.2 m, SD = 4.0 m) the receiver array (P < 0.001). Finally, the lowest positioning errors were detected in the area with the highest receiver density. Conclusions The VPS measures fish positioning in a reservoir, under suitable conditions, with satisfactory accuracy. We showed that the probability of location and the positioning error differed spatially in accordance with previous results in other conditions. Consequently, these analyses are recommended as a prerequisite to further spatial analyses using VPS-derived data.
Content may be subject to copyright.
A preview of the PDF is not available
... Fine-scale spatial acoustic telemetry has recently been used to understand the ecology of aquatic animals, such as centre-of-activity localisation, which is a method to provide a position estimated by the mean of the receiver's locations, weighted by the number of detections at each receiver (see the detail in Simpfendorfer et al. 2002Simpfendorfer et al. , 2008, as well as hyperbolic localisation, which is based on an algorithm using the time difference of arrival (TDOA) from at least three receivers (accuracy: 3-10 m; Vemco Radio-linked Acoustic Positioning, Vemco Inc.: Klimley et al. 2001;Zamora and Moreno-Amich, 2002;Mitamura et al. 2012b;Vemco Positioning System (VPS): Espinoza et al. 2011;Roy et al. 2014; High-Residence VPS: Guzzo et al. 2018; MAP System, Lotek Wireless Inc.: Cooke et al. 2005; multi-individual simultaneous 3D positioning, AquaSound Inc.: Takagi et al. 2018Takagi et al. , 2021. This acoustic telemetry approach provides fine-scale positional information about the home ranges (Teesdale et al. 2015), movement patterns Williams-Grove and Szedlmayer, 2016;Shoji et al. 2017), and homing behaviours (Mitamura et al. 2012b) of individuals predominantly in open water bodies such as seas, large lakes, and wide rivers. ...
... In this study, the performance of the zone monitoring method was compared with those of centreof-activity localisation (Simpfendorfer et al. 2002(Simpfendorfer et al. , 2008 and hyperbolic localisation (e.g. VPS: Vemco VR2W positioning system; Espinoza et al. 2011;Roy et al. 2014). For comparison, the same data derived from eight acoustic receivers deployed in the river were used. ...
... Hyperbolic localisation, such as localisation by using the VPS (Espinoza et al. 2011;Roy et al. 2014), accurately provides fine-scale horizontal positions (accuracy: 3-10 m) based on the TDOA. The TDOA of a signal to a given pair of receivers generates a set of potential source locations as a hyperbola. ...
Article
Full-text available
Fine-scale spatial acoustic telemetry, including hyperbolic and centre-of-activity localisation, is widely used to provide insight into the ecology of aquatic animals. However, these positional telemetry systems require numerous receivers, even for limited study areas such as narrow rivers, creeks, and canals, where tagged animals are typically monitored by receivers deployed at locations of particular interest or across a water body (acoustic gate). This paper proposes an acoustic zone monitoring method, which only uses a few acoustic receivers to estimate a zone used by a tagged fish in narrow water bodies. The effectiveness of the proposed method was verified by performing stationary and moving tests and by monitoring the movements of an invasive species in Japan, the channel catfish Ictalurus punctatus. Eight acoustic receivers were deployed 100–270 m apart along the river, with each zone having a length of 100–190 m. The proposed method provided accurate estimates in the inner and outermost zones of the eight stationary transmitters (100%, number of estimates: 1118 ± 419) and of a single transmitter towed by a boat (99.1%, number of estimates: 111/112). By contrast, centre-of-activity localisation estimated positions around the centre of the receiver array, and hyperbolic localisation was unable to provide positions because of an almost-straight-line array of receivers. The proposed zone monitoring method provided more accurate movement estimates of the tagged catfish. The method can cover an extended area using a limited number of receivers at a fine scale and be applied to initially identify the predominant habitats and distribution used by target species in the new study sites.
... A transmission can only be recorded by a receiver if it originates within the receiver's detection range. When a receiver array is designed such that detection ranges overlap (i.e. when receivers are spaced approximately 20-500 m apart; Roy et al., 2014;Trancart et al., 2020, and Figure 1 of Binder et al., 2017) and transmissions can be detected at multiple receivers, algorithms based on the differences among arrival times of a single transmission at multiple receivers can be used to calculate positions of the tagged animals on a spatially-continuous scale (e.g. Baktoft et al., 2017;Espinoza et al., 2011;Trancart et al., 2020). ...
... Positioning algorithms are often closed source (but see Trancart et al., 2020), expensive if carried out by the manufacturer, and the output can contain large amounts of error (Baktoft et al., 2017;Roy et al., 2014). ...
... that has dimension m × m, with q ii = − ∑ i,j≠i q ij , and all q ij > 0 for i ≠ j. The negatives of the diagonal elements, − q ii describe the rate of transition out of state i, that is, an animal will remain in state i for an amount of time that is exponentially distributed with rate parameter − q ii and mean − q −1 ii (Ross, 1996). The off-diagonal elements denote the rate of transitioning from state i to state j. ...
Article
Fine‐scale tracking with passive acoustic telemetry can yield great insights into the movement ecology of aquatic animals. To predict fine‐scale positions of tagged animals in continuous space from spatially‐discrete detection data, state‐space modelling through the R package YAPS provides a promising alternative to frequently used positioning algorithms. However, YAPS cannot currently classify multiple kinds of movement that may be used as proxies for individual behaviours of study animals (behavioural states), an endeavour that is of increasing interest to movement ecologists. We advance YAPS by incorporating the functionality to predict behavioural states by using an iterative maximization framework. Our model, which we call YAMS, occurs in continuous time and therefore we adapt current hidden Markov model (HMM) machinery to accommodate this while remaining within a likelihood framework that provides rapid fitting. We test our model using simulations and approximately 6 days’ worth of Northern pike data from Hald Lake, Denmark. YAMS is shown to produce accurate parameter estimates and random effect predictions when model results were compared to simulated data, with behavioural state accuracies of 0.94 and 0.79 for two‐ and three‐state models, respectively, and location state root mean squared errors of 1.8 m for both models. In addition, the behavioural states are shown to reflect varying speeds of the pike, yielding a highly interpretable classification. This research has the potential to be broadly applicable to both ecologists interested in identifying fine‐scale space use and behavioural states from acoustic telemetry data, as well as to statisticians who may wish to use standard HMM machinery to fit continuous‐time HMMs to animal movement data.
... This issue can be overcome by deploying a sufficient number of receivers to achieve complete coverage of a given area. For example, when the direction of migration is known or constrained in certain areas, using an array of receivers in a grid system in relatively enclosed study areas (e.g., lakes and estuaries) and using an array of receivers organized as a gate through which fish are likely to travel, have both been proved to be efficient methods to detect organisms (Heupel et al., 2006;Kraus et al., 2018;Roy et al., 2014). Despite being well suited for marine or lake environments, these solutions to increase the resolution of the data do not necessarily work well in river systems. ...
Article
Full-text available
The process of smolting is a critical phase in the life cycle of anadromous salmonids, and it has been associated with substantial rates of mortality. Survival during freshwater and marine migration is known to have population‐level effects; thus, an understanding of the patterns of mortality has the potential to yield important insights into population bottlenecks. Despite important advancements in tracking techniques, the specifics of mortality events in anadromous salmonids during their initial migration to sea remain somewhat elusive. Here, we develop a framework combining spatial and temporal detections of smolt riverine migration from two tracking techniques, which enable inferences to be made about mortality locations, causes, and rates. In this study, we demonstrate that during their initial riverine transitional phase, smolts were particularly vulnerable to predators. Specifically, avian predation appeared to be the main cause of mortality (42%), although piscine predation events were not trivial (14%). Our results suggested some direct and indirect tagging‐induced mortality (e.g., through increased predation vulnerability), which highlights the importance of determining tagging mortality in a telemetry study to ensure adequate interpretation of migration success. Overall, by estimating migration loss and its variability, our study framework should help to guide management actions to mitigate the widespread population declines these species are currently facing.
... To calculate error, the VPS analysis software uses the known positions of the reference transmitters to measure the distance between the triangulated position and the true position (HPEm), then calculates a second error estimate (HPE) that incorporates variation based on receiver array geometry and effects of depth, temperature, and salinity on the speed of signal transmission. However, the true location is only known for reference transmitters and not for animal transmitters, so the relationship between HPEm and HPE can only be examined for reference transmitters then subsequently applied to animal positions (Espinoza et al., 2011;Roy et al., 2014). For both VPS arrays separately, we created bins for all HPE values and plotted them against median HPEm values. ...
Article
Full-text available
Fundamental 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.
... It should be noted that the current review only incorporates VPS studies that had directly tagged animals as part of the study. During this search, 9 articles were identified which tested the mechanics of VPS (see the Supplement), including the factors influencing detection performance (Binder et al. 2014, 2016, Roy et al. 2014, Steel et al. 2014, Swadling et al. 2020. One additional article was feasibility-driven and studied the potential application of VPS to track turtle hatchlings (Thums et al. 2013); however, screening criteria identified understanding behavioural ecology as a primary focus. ...
Article
Recent advancements in telemetry have redefined our ability to quantify the fine-scale movements of aquatic animals and derive a mechanistic understanding of movement behaviours. The VEMCO Positioning System (VPS) is a fine-scale commercial positioning system used to generate highly accurate semi-continuous animal tracks. To date, VPS has been used to study 86 species, spanning 25 taxonomic orders. It has provided fine-scale movement data for critical life stages, from tracking day-old turtle hatchlings on their first foray into the sea to adult fish returning to natal rivers to spawn. These high-resolution tracking data have improved our understanding of the movements of species across environmental gradients within rivers, estuaries and oceans, including species of conservation concern and commercial value. Existing VPS applications range from quantifying spatio-temporal aspects of animal space use and key aspects of ecology, such as rate of movement and resource use, to higher-order processes such as interactions among individuals and species. Analytical approaches have seen a move towards techniques that incorporate error frameworks such as autocorrelated kernel density estimators for home range calculations. VPS technology has the potential to bridge gaps in our fundamental understanding of fine-scale ecological and physiological processes for single and multi-species studies under natural conditions. Through a systematic review of the VPS literature, we focus on 4 principle topics: the diversity of species studied, current ecological and ecophysiological applications and data analysis techniques, and we highlight future frontiers of exploration.
... The location of receivers in bays meant that significant sections sometimes fell outside the limit of direct line-of-sight between the receivers. Locating fish in the area outside of the line-of-sight receiver array boundary leads to greater positional error and less probability positions can be calculated (Espinoza et al. 2011, Roy et al. 2014. Additionally, the apex of most bays could not be effectively monitored due to the shadow effect behind the innermost receivers ( Figure 87, Smith 2013). ...
Technical Report
Full-text available
This study evaluated the relative effectiveness of three broad groups of fish attractors at attracting Australian bass and golden perch in impoundments to improve recreational angling. Comparisons were made between sunken structures constructed from timber and synthetic materials and a novel suspended fish attractor design. Multiple lines of evidence were used to evaluate the response. All types of fish attractors were used by the target species and the prey that supports them. Angler catch, visitation rates and satisfaction with the fishery all improved following installation of the fish attractors.
... While there is potential to leverage computer vision technology to monitor at the three-dimensional (Deakin et al., 2019), or individual level (Tidal, 2020), these are currently at a laboratory or research stage. An alternative approach is to tag individual fish to collect continuous data on the threedimensional positioning of individual fish within a cage (Roy et al., 2014). These provide very high temporal resolution of position but only a small subset of the total fish in the cage can be feasibly tracked. ...
Article
Full-text available
Aquaculture, or the farmed production of fish and shellfish, has grown rapidly, from supplying just 7% of fish for human consumption in 1974 to more than half in 2016. This rapid expansion has led to the growth of Precision Aquaculture concept that aims to exploit data-driven management of fish production, thereby improving the farmer's ability to monitor, control, and document biological processes in farms. Fundamental to this paradigm is monitoring of environmental and animal processes within a cage, and processing those data toward farm insight using models and analytics. This paper presents an analysis of environmental and fish behaviour datasets collected at three salmon farms in Norway, Scotland, and Canada. Information on fish behaviour were collected using hydroacoustic sensors that sampled the vertical distribution of fish in a cage at high spatial and temporal resolution, while a network of environmental sensors characterised local site conditions. We present an analysis of the hydroacoustic datasets using AutoML (or automatic machine learning) tools that enables developers with limited data science expertise to train high-quality models specific to the data at hand. We demonstrate how AutoML pipelines can be readily applied to aquaculture datasets to interrogate the data and quantify the primary features that explains data variance. Results demonstrate that variables such as temperature, wind conditions, and hour-of-day were important drivers of fish motion at all sites. Further, there were distinct differences in factors that influenced in-cage variations driven by local variables such as water depth and ambient environmental conditions (particularly dissolved oxygen). The framework offers a transferable approach to interrogate fish behaviour within farm systems, and quantify differences between sites.
... This issue can be overcome by deploying a 99 sufficient number of receivers to achieve complete coverage of a given area. For example, when 100 the direction of migration is known or constrained in certain areas, using an array of receivers in a 101 grid positioning system in relatively enclosed study areas (e.g., lakes and estuaries) or by using by 102 an array of receivers organised as a gate through which fish are likely to travel, have both been 103 proved to be efficient methods to detect organisms (Heupel et al. 2006, Roy et al. 2014, Kraus et 104 al. 2018. Despite being well suited for marine or lake environments, these solutions to increase 105 the resolution of the data do not necessarily work well in rivers systems. ...
Preprint
Full-text available
The process of smolting is a critical phase in the life-cycle of anadromous salmonids and it has been associated with substantial rates of mortality. Survival during freshwater and marine migration is known to have population level effects, thus an understanding of the patterns of mortality has the potential to yield important insights into population bottlenecks. Despite important advancements in tracking techniques, the specifics of mortality events in anadromous salmonids during their initial migration to sea remains somewhat elusive. Here, we develop a framework combining spatial and temporal detections of smolt riverine migration from two tracking techniques, which enable inferences to be made about mortality locations, causes, and rates. We embed this framework into a fine-scale behaviour study of migration and social structure. In this study, we demonstrate that during their initial riverine transitional phase, smolts were particularly vulnerable to predators. Specifically, avian predation appeared to be the main cause of mortality (42%), although piscine predation events were not trivial (14%). Our results suggested some direct and indirect tagging-induced mortality (e.g., through increased predation vulnerability), which highlights the importance of determining tagging mortality in a telemetry study to ensure adequate interpretation of migration success. There is evidence that predation induced selection on smolt morphology. Unsuccessful river salmon migrants with a phenotype comprising a shorter head and jaw and smaller eye had a higher probability of mortality in the later parts of riverine migration where avian and aquatic predation mortality dominated. In contrast, mortality earlier in river migration was independent of phenotype, most likely a result of tagging effects. Successfully river migrants were found to be interacting with each other, often in a pair or as a trio, indicating that a few individuals of Atlantic salmon and sea trout formed notable intra- and interspecific social associations. However, the heterogeneity of the social associations of successful migrants did not support the assumption that social network features attributed any clear specific benefits of reduced predation risk. Overall, by estimating migration loss and its variability, our study framework should help to guide management actions to mitigate the widespread population declines these species are currently facing.
... Consequently, these widely used tracking techniques that offer remote relay of positional data often cannot accurately define space-use by animals that move over small spatial scales (Thomson et al. 2017). Acoustic tracking provides one alternative for high resolution marine tracking, especially when equipped animals move inside an array of acoustic receivers (Roy et al. 2014), although one shortcoming of this approach is that animals are not located once they move away from receivers (Zeh et al. 2015, Lothian et al. 2018. ...
Article
Full-text available
Space use estimates can inform conservation management but relaying high‐accuracy locations is often not straightforward. We used Fastloc‐GPS Argos satellite tags with the innovation of additional data relay via a ground station (termed a “Mote”) to record high volumes (typically > 20 locations per individual per day) of high accuracy tracking data. Tags were attached in the Chagos Archipelago (Indian Ocean) in 2018‐2019 to 23 immature turtles of two species for which there have been long‐standing conservation concerns: 21 hawksbill turtles (Eretmochelys imbricata) and two green turtles (Chelonia mydas). Over long tracking durations (mean 227.6 days per individual), most turtles moved very little. For example, 17 of 21 hawksbill turtles remained continuously in the lagoon where they were equipped, with 95% and 50% Utilisation Distributions (UDs) averaging only 1.03 and 0.18 km2 respectively. Many individuals, and both species, could use the same small spaces, i.e., individuals did not maintain unique home ranges. However, three hawksbill turtles travelled 100s of km from the tagging site. Our results show that for some large marine vertebrates, even small protected areas of only a few km2 can encompass the movements of a large proportion of individuals over long periods. High accuracy tracking may likewise reveal the details of space use for many other animals that move little and/or use important focal areas and where previous low‐accuracy tracking techniques have tended to overestimate space use.
Article
Proper interpretation of gill‐net survey data requires knowledge of gill‐net encounter probabilities for target species, including understanding how variation in habitat use and movement rate affects encounter probability. However, few estimates of encounter probability exist. Further, previous studies hypothesize that gill‐net encounter probability is proportional to swimming speed, which increases with fish size. However, potential swimming speed may not be reflective of movement rates and encounter probability due to species specific biology and behaviors. I used a large telemetry dataset (483,169 positions) consisting of fine‐scale (< 5‐m resolution) Walleye Sander vitreus and saugeye Walleye x Sauger S. canadensis positions to simulate daily North American standard gill‐net surveys. I tagged and tracked forty‐two fish (340–614 mm) during both 2013 and 2014 and determined whether each fish position from April to November was within 24.8 m of shore (the length of the North American standard net). I also determined fish movement rate (m/h) during simulated gill‐net surveys and whether each fish track during each survey crossed 24.8 m “virtual” gill nets. I then used Bayesian multi‐level models to evaluate how nearshore habitat use, movement rate, and gill‐net encounter probability varied with fish length, species, and month. Movement rate (m/h) and gill‐net encounter probability were greatest for both Walleye and saugeye during April, May, and June, but neither movement rate nor encounter probability increased with fish length during most months. Walleye used nearshore habitats less frequently than saugeye, especially during September and November, resulting in lower gill‐net encounter probabilities for Walleye. These results show that gill‐net encounter probability varies across species, month, and occasionally fish length due to variation in both habitat use and movement rate. Further, these outcomes indicate that total gill‐net selectivity may change throughout the year due to changes in the relationship between fish length and gill‐net encounter probability.
Article
Full-text available
Acoustic telemetry systems are an increasingly common way to examine the movement and behaviour of marine organisms. However, there has been little published on the methodological and analytical work associated with this technology. We tested transmitters of differing power outputs simultaneously in several trials, some lasting ~50 days, to examine the effects of power output and environmental factors (water movement, temperature, lunar cycle and time of day). There were considerable and volatile changes in detections throughout all trials. Increased water movement and temperature significantly reduced detection rates, whereas daytime and full-moon periods had significantly higher detection rates. All nine transmitters (from seven transmitter types tested) showed a sigmoidal trend between detection frequency and distance. Higher-powered transmitters had a prolonged detection distance with near-maximal detections, whereas lower-powered transmitters showed an almost immediate decline. Variation of detection frequency, transmitter type and the modelled relationship between distance and detection frequency were incorporated into a positioning trial which resulted in markedly improved position estimates over previous techniques.
Article
Full-text available
We examined movement tracks of ultrasonic-tagged juvenile Chinook salmon (Oncorhynchus tshawyscha) smolts at the juncture of two migratory pathways. This migratory juncture occurs where the Delta Cross Channel splits from the Sacramento River in California’s Sacramento–San Joaquin Delta. Smolt tracks were analyzed to compare the importance of river flow and individual parameters in migratory route selection. The two routes differ significantly in smolt survival probabilities (Perry et al. N Am J Fish Manag 30:142–156, 2010), thus a clearer understanding of the variables contributing to route selection will be valuable for management of this declining species. A comparison of the two migratory groups showed that fish remaining within the Sacramento River: 1) Encountered the migratory juncture when river water velocities were much higher than those in the Delta Cross Channel (p < 0.0001), 2) showed more direct swimming paths (p = 0.03) and 3) migrated at higher speeds (p = 0.04). Logistic regression models showed that the ratio of mean water velocity between the two routes was a much stronger predictor of ultimate route selection than any other variable tested. However, parameters for both the lateral position of smolts within the river and smolt size added predictive power to the final model. Our results suggest that river flow remains the most important variable for predicting smolt migration route, but note that knowledge of individual smolt attributes and movement patterns can increase our predictive ability.
Article
Full-text available
Atlantic cod Gadus morhua exhibit multiyear homing to discrete spawning grounds, where they aggregate in dense schools. Within an aggregation, a series of complex mating behaviors takes place before mate selection and successful spawning. Disruption of these behaviors has been suggested as a cause of diminished reproductive success and poor recruitment in some stocks. An area known to support a spawning aggregation in Massachusetts Bay was closed to both commercial and recreational fishing for the months of May and June 2009. During the closure period, 10 Atlantic cod were captured, tagged with acoustic transmitters, and released back to the aggregation. Four stationary acoustic receivers were deployed in the area to record transmissions from the tagged fish. Overlapping detection ranges of the receivers allowed for the reconstruction of fine-scale movements of the tagged fish over several days. The tagged cod showed a consistent pattern of aggregation prior to the fishery, characterized by limited movement and similar space use. With the opening of the fishery, the aggregation behavior was disrupted, resulting in increased horizontal and vertical movements and dissimilar space use among individuals. Half of the tagged fish appeared to have been caught in gill nets within 9 h of the opening, while the remainder left the area within 18 h. Even though the receivers were maintained for 9 d after the opening, none of the tagged fish that left the area returned. These results indicate that the spawning aggregation was completely dispersed by the onset of the fishery. Managers hoping to protect spawning aggregations should be aware that the effects of fishing on a spawning aggregation go beyond the removals from the spawning stock.Received May 3, 2011; accepted October 13, 2011
Article
We attached sonic transmitters to, and tracked, 40 giant Pacific octopuses (Enteroctopus dofleini) ranging from < 1 to 21 kg in size in south-central Alaska using near-continuous tracking by fixed-array receivers and intermittent tracking with a mobile receiver. We documented area use, daily activity patterns, spatial scale of movements and whether these differed by octopus size, and whether octopuses actively selected habitats. Near-continuous fixed tracking provided positions about every 4 min over a limited area, while intermittent mobile tracking provided positions every 1–6 h but over open and larger areas. Mantle-mounted transmitters on modified Peterson disks had > 83% retention to the end of a tracking period (range < 1 day [before animal left the study area] to at least 88 days post-release), an improvement over published studies. Octopuses were found to be stationary or hiding 94% of the time. Otherwise, octopuses were active throughout the day but more so from midnight to 0500. During low tides, movements were restricted for animals in intertidal habitats but not for those deeper. Maximum movement distance from release was 4.8 km (by a 16.5 kg female). Minimum convex polygon area use averaged 4,300 m2 for the smallest animals to an average over 50,000 m2 for the largest during 2 to 20 days of tracking, substantially larger than previously reported. Larger octopuses moved further and used greater area than smaller animals, but differences between sexes were not significant.
Article
The development of miniature acoustic transmitters and economical, robust automated receivers has enabled researchers to study the movement patterns and survival of teleosts in estuarine and ocean environments, including many species and age-classes that were previously considered too small for implantation. During 2001–2003, we optimized a receiver mooring system to minimize gear and data loss in areas where current action or wave action and acoustic noise are high. In addition, we conducted extensive tests to determine (1) the performance of a transmitter and receiver (Vemco, Ltd.) that are widely used, particularly in North America and Europe and (2) the optimal placement of receivers for recording the passage of fish past a point in a linear-flow environment. Our results suggest that in most locations the mooring system performs well with little loss of data; however, boat traffic remains a concern due to entanglement with the mooring system. We also found that the reception efficiency of the receivers depends largely on the method and location of deployment. In many cases, we observed a range of 0–100% reception efficiency (the percentage of known transmissions that are detected while the receiver is within range of the transmitter) when using a conventional method of mooring. The efficiency was improved by removal of the mounting bar and obstructions from the mooring line.