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An overview of electronic tags that can be used in fish research is given, including radio and acoustic transmitters, data storage tags (DST, also termed archival tags), pop-up satellite archival tags (PSAT) and passive integrated transponder tags (PIT-tag). Fish telemetry is a term used to describe the application of these methods. Typically, an electronic tag is attached to a free-swimming fish, and information on position, movements and/or measurements of environmental and physiological parameters can be recorded wirelessly by use of a mobile receiver or stationary loggers. For most methods, the fish need not to be recaptured to achieve data. However, DSTs record and store information on environmental and/or physiological parameters in the tag, and therefore need to be retrieved for downloading data. In the case of PSATs, stored data is transferred to satellites when the tag loosens from the fish and pops up to the surface, and in addition, the pop up position is recorded. The developments of telemetry methods have provided opportunities to reveal previously unknown information on fish behavior, habitat use and migrations in fresh water, estuaries, near-coastal areas and oceans, especially since extensive long-term data can be collected repeatedly from individual fish. Detailed information on fish behaviour and migrations is needed to better understand, protect and manage fishes in freshwater and marine systems. The development of successful management measures depends on knowledge of where fish reside and migrate during the day, season and year. There has been a tremendous increase in the use of electronic tagging methods, especially during the last 10-20 years. In addition to descriptive and ecological studies, the methods have been used to assess effects of for instance hydropower production, other river regulations, migration barriers, protected areas, fishing regulations, catch-and-release angling, hatchery-rearing, fish aggregating devices (FADs), water pollution and aquaculture. The main methods for attaching electronic tags to fish are 1) surgical implantation in the body cavity, 2) external attachment, and 3) gastric insertion via the mouth. Potential negative handling effects are inflammations, infections, tag expulsion, altered behavior, decreased swimming performance, reduced feeding, reduced growth and increased mortality. The catch, handling and tagging procedures should have minimal effects on the fish. If not, an anomalous behaviour caused by the tagging may be recorded instead of the natural behaviour, and the study is a failure from a scientific point of view. Furthermore, optimal anaesthetic and tagging methods are required to meet the ethical standards for use of experimental animals, and to ensure fish survival and welfare.
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... Acoustic telemetry Acoustic telemetry uses underwater receivers (hydrophones) to detect fish that have been tagged with sound-emitting transmitters. Individual fish can be recognised by using transmitters with a unique combination of frequency and pulse rate or by using coded signals (Thorstad et al. 2013). Acoustic telemetry is particularly useful for studying fish distributions, migrations and behaviours, including in marine and estuarine environments (Dames et al. 2017), but necessarily requires fish to be captured (in good condition) so that they can be tagged with a transmitter (Cooke et al. 2011). ...
... Tagged fish can be detected automatically (using stationary receivers) or manually (using mobile receivers), but the receivers must be submerged in water and unobstructed (e.g. by debris). Stationary receivers can be deployed on the substratum or in the water column at strategic locations, and the data downloaded by cable or bluetooth transfer at intervals or the end of the study (Thorstad et al. 2013). The detection ranges of acoustic transmitters can vary from tens of metres to a few kilometres and depend partly upon their signal strength (Pincock & Johnston 2012). ...
... The detection ranges of acoustic transmitters can vary from tens of metres to a few kilometres and depend partly upon their signal strength (Pincock & Johnston 2012). The strength of acoustic signals is determined by the battery (and hence transmitter) size, with strong signals (and high pulse rates and long-term studies) requiring large batteries (Thorstad et al. 2013). In addition, large transmitters produce low-frequency sound, which penetrates greater distances underwater than do higher frequencies (Pincock & Johnston 2012). ...
Chapter
This appendix examines the field methods for fish monitoring in estuaries, including ‘traditional’ sampling techniques (nets and traps), and the more recent acoustic and visual detection, and DNA‐based methods. The features, advantages and disadvantages of each technique are presented (e.g. applicability to given habitat conditions, selectivity, efficiency, standardisation and fitness‐for‐purpose for recording different aspects of fish ecology), with best practice examples from study cases worldwide. The context of monitoring strategies for fish in estuaries, including legislative constraints and requirements, as well as key considerations for designing a fish monitoring programme (e.g. spatial and temporal variability) is also given.
... Electronic transmitters are widely used to study fish behavior, spatial ecology, and survival [1] [2] [3] [4] [5]. They can be attached externally, inserted into the gastric system, or inserted into the body cavity [6] [7] [8] [9]. ...
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A novel sutureless surgical technique has been successfully used to implant acoustic transmitters in relatively large rainbow trout Oncorhynchus mykiss with a tag-to-body-ratio of 0.88%. This study examined the same technique in smaller rainbow trout in two, 12-week trials comparing both sutured and sutureless surgical techniques. In the first trial using a tag-to-body-ratio of 1.9% ± 0.04%, tag retention was only 16.6% in fish without sutures, which was significantly lower than the 83.3% retention with sutured incisions. Similarly, in the second trial with a tag-to-body-ratio of 3.2% ± 0.03%, tag retention was 55.5% without sutures, which was significantly lower than the 90.0% retention using sutures. Mortality was not significantly different between treatments in either trial. The results of this study indicate that sutures must be used during surgeries to implant acoustic transmitters in relatively smaller fish with tag-to-body-ratios at or above 1.9%.
... A variety of techniques have been used to collect data on animal movement in the marine environment, mostly based on mark-and-recapture methods (Lucas and Baras 2000) and biotelemetry (Thorstad et al. 2013). The choice of the appropriate technique relies on the objective and scope of each study, life stage, body size, spatial and temporal scale, and the level of investigation (from individuals to population). ...
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The white seabream Diplodus sargus (L., 1758) (Osteichthyes, Sparidae) is a littoral species living mainly in rocky habitats and distributed in the eastern Atlantic and the Mediterranean. This species is targeted by artisanal and recreational fisheries and presents a high commercial importance. Although classified by IUCN as a “least concern” species, it has been the object of marine ranching and restocking initiatives to counteract locally intense exploitation. Here, we review the current knowledge on the movement ecology of white seabream given the relevance of animal movement in ecological and behavioral studies and their potential application in management and conservation. The literature on this topic was analyzed in order to summarize the results of past research and to identify the gaps that still exist on the matter. We reviewed a total of 27 papers focusing on the movement ecology of white seabream, where acoustic telemetry (n = 12), underwater visual observation and traditional tagging (n = 6), genetic analysis (n = 6), and otolith microchemistry (n = 3) were used. While the first three methods were applied to juvenile and adult fish, the last one was also used with larvae, which have been the object of experimental trials to ascertain their swimming abilities. The largest amount of information on activity rhythms (diurnal with a few exceptions), movement patterns (short distances), homing (ability to come back to the capture site), site fidelity (high), and home range (< 200 ha on average and highly related with seabed morphology) were obtained through acoustic telemetry, whose main limitation is the minimum body size required for its application. The environmental variables found to affect movement patterns in this species are water temperature (which triggers spawning-based vertical movements), local sea conditions (which affect short-scale movements in juveniles), and the main seabed features (orientation and habitat type). The main gaps identified, which need more extensive research and some technological improvements, include the study of the effects of environmental variables on fish movements and further investigations on the movement patterns of juveniles.
... Remote Underwater Video (RUV) recording in marine applications (Zarco-Perello and Enríquez, 2019) has shown great potential for fisheries, ecosystem management, and conservation programs (Piggott et al., 2020). With the introduction of consumer-grade high-definition cameras, it is now feasible to deploy a large number of RUVs or Autonomous Underwater Vehicles (AUVs) to collect substantial volumes of data and to perform more effective monitoring (Pope et al., 2010;Rasmussen and Morrissey, 2008;Thorstad et al., 2013). However, underwater habitats introduce diverse video monitoring challenges such as adverse water conditions, high similarity between fish species, cluttered backgrounds, and occlusions among fish. ...
Article
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Marine scientists use remote underwater image and video recording to survey fish species in their natural habitats. This helps them get a step closer towards understanding and predicting how fish respond to climate change, habitat degradation and fishing pressure. This information is essential for developing sustainable fisheries for human consumption, and for preserving the environment. However, the enormous volume of collected videos makes extracting useful information a daunting and time‐consuming task for a human being. A promising method to address this problem is the cutting‐edge deep learning (DL) technology. DL can help marine scientists parse large volumes of video promptly and efficiently, unlocking niche information that cannot be obtained using conventional manual monitoring methods. In this paper, we first provide a survey of computer visions (CVs) and DL studies conducted between 2003 and 2021 on fish classification in underwater habitats. We then give an overview of the key concepts of DL, while analysing and synthesizing DL studies. We also discuss the main challenges faced when developing DL for underwater image processing and propose approaches to address them. Finally, we provide insights into the marine habitat monitoring research domain and shed light on what the future of DL for underwater image processing may hold. This paper aims to inform marine scientists who would like to gain a high‐level understanding of essential DL concepts and survey state‐of‐the‐art DL‐based fish classification in their underwater habitat.
... Cependant l'utilisation d'une telle technologie pour estimer le taux métabolique des poissons nécessite d'être calibrée à l'aide de mesures de la consommation en oxygène car celle-ci varie aussi en fonction de nombreux facteurs biotiques ou abiotiques comme la température ou la pression partielle en oxygène (Thorstad et al., 2013, Alonzo et al., 2021. La mesure seule des EMG des poissons peut se révéler alors insuffisante afin d'étudier l'impact de l'environnement sur les déplacements des poissons. ...
Thesis
La très grande majorité des organismes vivants se déplacent au cours de leur vie et ce à des échelles spatio-temporelles très contrastées, du butinage des abeilles aux migrations emblématiques des baleines à bosses entre les tropiques et les pôles. L’un des grands défis des écologistes du mouvement reste encore aujourd’hui de mieux comprendre les relations entre physiologie et déplacement, souvent gouvernées par les variations environnementales. Le cœur est un organe vital dont les battements reflètent directement les variations physiologiques imposées par l’environnement.Ce travail de doctorat, par une approche couplée de télémétrie acoustique et d’écophysiologie expérimentale, cherche à mieux comprendre l’impact de l’environnement (1) sur les déplacements de trois espèces de poissons côtiers emblématiques du golfe du Lion, la daurade royale Sparus aurata, le loup Dicentrachus labrax et la saupe Sarpa salpa, au sein de leur site d’alimentation en milieu lagunaire ainsi que (2) sur leurs migrations vers la mer. Les résultats montrent que les trois modèles biologiques sont fortement résidents dans la lagune pendant la période d’alimentation et y sont fidèles inter-annuellement, confirmant ainsi l’importance du milieu lagunaire strict au sein de leur cycle de vie. Le développement d’une technique d’implantation de capteurs mesurant la fréquence cardiaque de daurades d’élevage en nage libre s’est révélé efficace pour déterminer des seuils de tolérance pertinents au réchauffement. Cette technique a été appliquée pour la première fois à des daurades sauvages afin de déterminer des seuils de tolérance à la baisse ou à la hausse de températures et de les relier aux mouvements observés en milieu naturel. Les conclusions sont que (1) la température semble avoir très peu d’influence sur l’utilisation de l’espace lagunaire des daurades en phase d’alimentation, mais (2) qu’elle est le principal déclencheur de migrations de refuge vers la mer durant les épisodes de forte chaleur et vraisemblablement le principal facteur empêchant les daurades d’hiverner au sein de la lagune. Enfin, (3) la photopériode, probablement en lien avec la température, apparait comme le principal déclencheur des départs en migrations de reproduction des daurades, ce que leur synchronisation de ces départs semble confirmer. L’étude des réponses cardiaques au réchauffement a montré que 29°C est un seuil de tolérance pertinent au réchauffement ce qui semble être en accord avec les températures initiant les migrations de refuge. En revanche, aucun seuil n’a pu être clairement identifié à partir de la réponse cardiaque au refroidissement.Plus généralement, cette étude démontre la pertinence d’une approche multidisciplinaire pour l’étude des mouvements.
... Remote Underwater Video (RUV) recording in marine applications (Zarco-Perello and Enríquez, 2019) has shown great potential for fisheries, ecosystem management, and conservation programs (Piggott et al., 2020). With the introduction of consumer-grade high-definition cameras, it is now feasible to deploy a large number of RUVs or Autonomous Underwater Vehicles (AUVs) to collect substantial volumes of data and to perform more effective monitoring (Pope et al., 2010;Rasmussen and Morrissey, 2008;Thorstad et al., 2013). However, underwater habitats introduce diverse video monitoring challenges such as adverse water conditions, high similarity between fish species, cluttered backgrounds, and occlusions among fish. ...
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Marine scientists use remote underwater video recording to survey fish species in their natural habitats. This helps them understand and predict how fish respond to climate change, habitat degradation, and fishing pressure. This information is essential for developing sustainable fisheries for human consumption, and for preserving the environment. However, the enormous volume of collected videos makes extracting useful information a daunting and time-consuming task for a human. A promising method to address this problem is the cutting-edge Deep Learning (DL) technology.DL can help marine scientists parse large volumes of video promptly and efficiently, unlocking niche information that cannot be obtained using conventional manual monitoring methods. In this paper, we provide an overview of the key concepts of DL, while presenting a survey of literature on fish habitat monitoring with a focus on underwater fish classification. We also discuss the main challenges faced when developing DL for underwater image processing and propose approaches to address them. Finally, we provide insights into the marine habitat monitoring research domain and shed light on what the future of DL for underwater image processing may hold. This paper aims to inform a wide range of readers from marine scientists who would like to apply DL in their research to computer scientists who would like to survey state-of-the-art DL-based underwater fish habitat monitoring literature.
... Biotelemetry, including the use of small acoustic transmitters, is frequently applied to provide insight into the ecology (e.g. habitat use and movement patterns) of free-ranging aquatic animals, such as fishes and sea turtles (Cooke et al. 2004;Thorstad et al. 2013;Hussey et al. 2015;Hays et al. 2016;Matley et al. 2021). The tagged animals are either tracked manually or using stationary receivers that detect and record the presence of transmitters when they are within the detection range of the receiver, approximately 300-800 m (Heupel et al. 2006;Hedger et al. 2008;Mitamura et al. 2012a;Kessel et al. 2014). ...
Article
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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.
... In the current study, we used acceleration-logging popup archival transmitting (PAT) tags to infer individual survival outcomes for Pacific Halibut released in situ following capture on longlines. These tags have proven effective for studying a variety of aspects of the biology of marine fishes (Thorstad et al. 2013). The PAT tags used in our study were capable of detecting and recording acceleration for periods in excess of 3 months, allowing for individual fish activity to be inferred. ...
Article
Pacific Halibut Hippoglossus stenolepis captured in directed commercial longline fisheries in Canada and the USA that are below the legal minimum size for retention must be returned to the sea without incurring additional injury. Estimates of mortality caused by discarding sublegal‐sized fish are included in annual estimates of total mortality from all sources and affect the results of stock assessment and the yield available to fisheries. Currently, an average discard mortality rate (DMR) of 16% is applied to all sublegal‐sized longline discards. These discards consist of fish that suffer injuries ranging from minor to severe. The 16% DMR that is currently applied was derived by averaging injury‐specific DMRs that in turn assume 3.5% mortality of Pacific Halibut that are released to the sea with only minor injuries. The latter has been derived experimentally but only in captivity. Here, we used acceleration‐logging pop‐up archival transmitting tags to infer individual survival outcomes for Pacific Halibut that were released in situ following capture on longline gear. Postrelease behavioral data were evaluated for 75 fish that were at liberty for 2–96 d. Three fish were confidently inferred to have died after periods at liberty of 41–80 d, and another three fish may have died 96 d after release, resulting in minimum and maximum estimated 96‐d postrelease DMRs of 4.2% (range = 0.0–8.7%) and 8.4% (range = 1.7–14.6%), respectively. These ranges are consistent with the currently applied value of 3.5%. However, the observation that no mortalities occurred until after 40 d postrelease departs from the findings of captive studies, in which the majority of capture‐induced mortality occurred within 20 d of release.
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The regulation of river flow by dams of hydroelectric power plants (HPPs) has a significant impact on the populations of migratory fish species, preventing their movement between the upstream and downstream sections. Violation of the level and thermal regime of the river in the downstream of the HPP can also lead to a modification of the migration process, both within the main channel and between the main channel and its adjoining system. It is assumed that after the construction of the dam of the Krasnoyarsk hydroelectric power station, a significant part of the population of the Baikal grayling Thymallus baicalensis in the downstream section switched to a sedentary lifestyle. However, quantitative assessments of this phenomenon have not yet been carried out. The middle course of the Yenisei River in the downstream of the HPP is a specific watercourse with a smoothed seasonal amplitude of water temperatures and a high biomass of benthic invertebrates, up to 10-30 g/m2. Such conditions provide an increase in the growth rate of grayling in the main channel of the Yenisei, and lead to the formation of the structure of its scales, which differs from fish from the tributaries of the Yenisei. An additional feature of the Yenisei in the downstream of the HPP is that the content of technogenic radionuclides, in particular, radiocesium, 137Cs, increased compared to the background levels, below the point of radioactive discharges of the Mining-and-Chemical Combine ROSATOM (MCC) located near the town of Zheleznogorsk (Fig. 1). Thus, high growth rates, a unique structure of scales, and an increased concentration of radiocesium can be considered as markers of grayling that constantly inhabit the main channel of the Yenisei in the downstream of the Krasnoyarsk HPP. Within the framework of this work, we for the first time attempted to assess the ratio of settled and migrated individuals of the Baikal grayling from the tributaries in the thermally altered section of the Yenisei on the basis of the structure of the scales. As a verification of the proposed marker, we used the linear dimensions of fish and the content of radioactive cesium in their tissues. A sample of 161 individuals of the Baikal grayling was used in this work. Fish were collected in the section of the main channel of the Yenisei near the mouth of the Kan River, near the village. Khloptunovo (56º28′05″ N, 93º38′53″ E) in July–November 2019. Fork Length and total weight of fish were measured. Grayling scales taken in the lateral line region were photographed and then used to count the number of sclerites in the completed annual rings. The principle of differentiation of grayling individuals by their origin is based on previously obtained results on an increased number of sclerites on the scales of fish (primarily in the second annual ring) inhabiting a thermally altered section of the middle reaches of the Yenisei. Within the framework of this study, we assumed that individuals of grayling with more than 15 sclerites in the second annual ring of scales constantly inhabit the main channel of the thermally altered section of the Yenisei. Further, these individuals are designated by the term "sedentary". Individuals with a smaller number of sclerites, designated as “migrants,” spent at least the second year of their life in tributaries. To measure the content of technogenic radionuclides, fish of the two indicated types were isolated from the total sample. In the pooled samples of sedentary grayling for each month, the number of individuals varied from 12 to 31 (total 125), in the samples of migratory ones - from 3 to 8 individuals (total 18). Samples were prepared from muscles taken from the axial skeleton of fish, dried and ashed in a muffle furnace at 450°C. The content of γ-emitting radionuclides in the ash samples was measured using a gamma spectrometer with a hyper-pure germanium detector GX2320 (Canberra). The spectra were analyzed using the Genie-2000 software (Canberra). The number of sclerites in the second annual ring of the studied grayling varied from 9 to 24. The share of individuals with from 9 to 14 sclerites, and designated in our work as migrants, was 18.6% of the entire sample (Fig. 2). The highest percentage of migrating individuals was recorded in July (24%), in August-September it was about 20-22%, in October - 15%, and in November such grayling was not found. To assess potential differences in the growth rates of sedentary and migratory fish, the samples were divided into groups by age and month of capture. The linear dimensions of the sedentary grayling aged 2–3 + were 3-5 cm higher (p <0.05) than the linear dimensions of migrating fish in July–August (Fig. 3). There were no differences in FL in 4+ year old fish in July, as well as in 3-year-old fish in September–October. Of the technogenic gamma-emitting radionuclides, only radiocesium was registered in the muscles of grayling (137Cs, half-life - 30.1 years). The content of 137Cs in grayling muscles varied in the range of 0.9–7.2 Bq/kg. The maximum content of 137Cs was noted in sedentary fish in August, which exceeded the content of this radionuclide in the sample of migrants by six times (Fig. 4). In the rest of the months, the samples of sedentary and migrating individuals contained a similar specific activity of 137Cs. In July, the content of radiocesium in the sample of migrating individuals was not measured. The content of radiocesium in the muscles of grayling caught in the background site of the Yenisei did not exceed the detection limits. Thus, for 2-3-years-old fish, caught in the summer period, the assumption about the differences in the growth rates and the content of radionuclides in the tissues of residential and migratory individuals was confirmed. To explain the absence of differences between individuals of the two strategies in other months, a temperature model of the distribution of grayling in the tributaries of the Yenisei was proposed. According to our assumption, when the water temperature rises to the physiological optimum (17-18°C) in the lower and middle reaches of the tributaries in July-August, part of the local fish rises upstream, and part rolls down into the colder Yenisei (summer temperatures no more than 12°C). It is during this period that the most dramatic differences between the Yenisei fishes and migrants can be diagnosed. By mid-late autumn, such differences are leveled, and the migrants themselves are scattered among the Yenisei fish (Fig. 5). The reason for the increased content of 137Cs in sedentary grayling in August is not clear to us, but, possibly, it is due to the dynamics of permitted radioactive discharges into the Yenisei, the frequency of which during the year is not known to the authors, since it is not published in the annual radioecological reports. Cesium, being a chemical analogue of potassium, behaves in the body of fish similarly to this biogenic element. The main deposits of cesium are found in fish muscles. When balancing the intensity of consumption and excretion of radiocesium, its content in the tissues of sedentary individuals reaches a stationary level, which we observed in September-November. The results of the work show that fish isolated from the general sample on the basis of a smaller number of sclerites in the second annual ring can indeed be considered migrants from tributaries. The approach we used reveals predominantly immature and first maturing individuals settling from tributaries, but is unsuitable for identifying sexually mature fish that carry out short-term intra-river migrations. In the thermally altered section of the Yenisei in the downstream of the HPP, tributaries can still make a significant contribution to the grayling population. In the area of the mouth of the Kan River, one of the largest tributaries of the middle Yenisei, the percent of migrants in the summer-autumn period of 2019 was about 20% of the total grayling population. The need to separate sedentary and migratory individuals is important for obtaining homogeneous samples of grayling, which is traditionally used as a model object in analyzing the distribution of technogenic pollutants in the river, as well as for studying the nutritional value of grayling and environmental risks for the population associated with its consumption.
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The search for effective strategies to prevent and mitigate accidental releases of aquaculture fishes is on-going. To test a new recapture strategy and evaluate the individual dispersal behaviour of escaped farmed Atlantic salmon Salmo salar L. at the northern limit of its range, 39 adult salmon (mean +/- SD fork length and weight: 85.5 +/- 5.0 cm and 7.4 +/- 1.4 kg, respectively) were implanted with depth-sensing acoustic tags and released in a north Norwegian fjord during the spring of 2007. The fish were released from 2 aquaculture sites in the Altafjord system and tracked using both mobile and fixed receivers. The coastal marine bag-net fishery, in combination with in-river angling, was tested as a potential recapture strategy. Immediately following the simulated escape event, the fish dove to near-bottom depths, subsequently returning to surface levels within the following days. The fish dispersed rapidly (9.5 +/- 19.2 km d(-1)), traveling outward to coastal waters along the edges of the fjord. The bag-net fishers and anglers recaptured 79% of the escaped fish within 1 mo post-release, 90% of which were from bag nets. While most of the fish left the fjord, 7 tagged fish (18%) entered the Alta River estuary (3 of which later migrated up the Alta River), and 1 returned to the Altafjord the following year, presumably to spawn. The results showed that recapture efforts need to be immediate and widespread to mitigate farm-escape events. Coastal bag nets were effective at recapturing escaped farmed salmon, compared to previously tested methods, and would be especially useful in areas where gill-netting is not permitted.
Article
Telemetric and molecular techniques are powerful tools for investigating patterns of species dispersal, habitat use, and reproductive behavior. Yet, these methods are rarely combined when studying spatial structures of migrating animals. This study combines migration data with genetic assignment tests of radio-tagged sea trout, Salmo trutta L., in two Swedish rivers. We investigate how the genetic information enhances the interpretation of the telemetry data. Individual gene frequencies of tagged fish are assigned to baseline samples of brown trout collected in tributaries and the main stems. The genetic assignment tests confirm that individuals returned from the sea to their natal stream, but also suggest that some individuals migrated to other than their native habitat. In total, 82% (R. Pitealven) and 37% (R. Vindelalven) of fish that were successfully assigned to a sample in a baseline migrated to an area in the vicinity of the sample location. The difference between rivers is likely due to low genetic differentiation among baseline samples and effects of stocking of fish in the R. Vindelalven. Combining the two techniques enhances understanding of migration behavior, important for conservation and management.
Chapter
While data storage tags typically provide information about depth and temperature, the horizontal position of fish is difficult to obtain. The objective of this study is therefore to introduce a method for reconstructing horizontal migration patterns of fish tagged with DSTs. The method works by: establishing a database on bathymetry and environmental information about the target area, moving a large number of virtual fish between the release and recapture positions using a biased random walk procedure, and then terminate trajectories where the information at position is in disagreement with the tag information. For example a trajectory is terminated if the tag depth is greater than the bottom depth. The method is exemplified with two tag recordings from Northeast Arctic cod (Gadus morhua L.) in the Barents Sea. The results show that termination of impossible trajectories limits the number of potential trajectories between release and recapture positions, and in particular the usage of multiple termination criteria (depth and temperature) proved to be effective in reducing the number of possible trajectories. The method is general, simple to use, and can also be used in combination with geolocation methods.
Article
A fish aggregating device (FAD) called a payao is conventionally installed to catch pelagic species in the Philippines. The waters around the Philippines are important regions for yellowfin tuna stocks because they include spawning grounds and nurseries. To understand the schooling behavior of juvenile yellowfin tuna Thunnus albacares around a payao, 13 juveniles (20.5-24.0 cm fork length) double tagged with ultrasonic transmitters (V7-2L-R256; Vemco Ltd.) and data loggers (DST-micro; Star-Oddi Ltd.) were released around a payao. A self-recording receiver (VR2-DEL; Vemco Ltd.) was attached on the mooring rope of the payao to follow the horizontal movements and data loggers recorded the vertical movements of tagged juveniles. Nine juveniles were recaptured simultaneously by ring net at the same payao after 4-7 days. One juvenile was recaptured by hand line at another payao 12 km away from the tagging site after 6 days. Recaptured juveniles showed a diurnal schooling pattern suggesting different school shape and foraging strategy between daytime and nighttime. Juveniles showed a diurnal horizontal moving pattern, concentrated near the payao during daytime, while they were distributed around the payao at nighttime. The fluctuations of swimming depth were synchronized among fish. Juveniles also showed a diurnal vertical movement pattern in surface mixed layer. They concentrated in a shallow and narrow range (11.2 +/- 8.2 m, mean +/- SD) at nighttime, while they were distributed to a deep and wide range (20.0 +/- 11.8 m) during daytime. The maximum vertical neighbor distance indicated the vertical thickness of the school and showed a peak around noon. Higher vertical movement speed during daytime indicated vertical foraging in a water column, while at nighttime the juveniles might forage horizontally following the diurnal migration patterns of prey in the surface layer.