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Abstract Over the past decades, tracking technologies have become more ubiquitous and helped uncover crucial spatiotemporal relationships in nature. In order to apply these technologies to small animals and reduce any potential adverse impact of devices, geopositioning methodologies compatible with lightweight devices are highly sought after. Measured by lightweight geolocators, atmospheric pressure provides an untapped opportunity for global geopositioning, as its natural temporal variation is unique to each location. In this study, we estimate the position of birds by comparing pressure data recorded by the geolocator with reference data from a global weather reanalysis database. The method produces a likelihood map of the position based on (1) a mask of the locations for which the ground‐level elevation matches the pressure measured by the geolocator and (2) a mismatch between the temporal time series measured by the geolocator and the reanalysis dataset. This new method is introduced step by step and applied to 16 tracks of nine long‐ and short‐distance migrant species. Using known positions of double‐tagged individuals (light and pressure data), we demonstrate that our method is almost three times more accurate than light‐based positioning with an average error of 44 km in our trials. In contrast to the traditional light‐based approach, pressure geolocation can provide useful information for short stationary periods (less than a day) and is not affected by the equinox problem nor by any shading effects due to weather or animal behaviour. To facilitate the application of the method, we developed an R package GeoPressureR, together with a user guide GeopressureManual and starting code GeoPressureTemplate. The use of pressure sensors to position animals has the potential to become widespread thanks to the combination of both affordable lightweight devices (100 km), forest‐dwelling species, nocturnal animals and altitudinal migrants.

Abstract Tracking technologies have widely expanded our understanding of bird migration routes, destinations and underlying strategies. However, determining the entire trajectory of small birds equipped with lightweight geolocators remains a challenge. We develop a highly optimized hidden Markov model (HMM) for reconstructing bird trajectories. The observation model is defined by pressure and, optionally, light measurements, while the movement model incorporates wind data to constrain consecutive positions based on realistic airspeeds. To reduce the computational costs associated with a large state space, we prune the HMM states and transitions based on flight and observation constraints to efficiently model the entire trajectory. The approach presented is based on a mathematically exact procedure and is fast to compute. We demonstrate how to compute (1) the most likely trajectory, (2) the marginal probability map of each stationary period, (3) simulated trajectories and (4) the wind conditions (wind support/drift) encountered by the bird during each migratory flight. We construct a version of an HMM optimized for reconstructing a bird's migration trajectory based on lightweight geolocator data. To render this approach easily accessible to researchers, we designed a dedicated R package GeoPressureR (https://raphaelnussbaumer.com/GeoPressureR/).

Tracking technologies have widely expanded our understanding of bird migration routes, destinations and underlying strategies. However, determining the entire trajectory of small birds equipped with lightweight geolocators remains a challenge.We develop a highly optimized hidden Markov model (HMM) for reconstructing bird trajectories. The observation model is defined by pressure and, optionally, light measurements, while the movement model incorporates wind data to constrain consecutive positions based on realistic airspeeds. To reduce the computational costs associated with a large state space, we prune the HMM states and transitions based on flight and observation constraints to efficiently model the entire trajectory.The approach presented is based on a mathematically exact procedure and is fast to compute. We demonstrate how to compute (1) the most likely trajectory, (2) the marginal probability map of each stationary period, (3) simulated trajectories and (4) the wind conditions (wind support/drift) encountered by the bird during each migratory flight.We construct a version of an HMM optimized for reconstructing a bird's migration trajectory based on lightweight geolocator data. To render this approach easily accessible to researchers, we designed a dedicated R package GeoPressureR (https://raphaelnussbaumer.com/GeoPressureR/). [ABSTRACT FROM AUTHOR]

Over the past decades, tracking technologies have become more ubiquitous and helped uncover crucial spatiotemporal relationships in nature. In order to apply these technologies to small animals and reduce any potential adverse impact of devices, geopositioning methodologies compatible with lightweight devices are highly sought after. Measured by lightweight geolocators, atmospheric pressure provides an untapped opportunity for global geopositioning, as its natural temporal variation is unique to each location.In this study, we estimate the position of birds by comparing pressure data recorded by the geolocator with reference data from a global weather reanalysis database. The method produces a likelihood map of the position based on (1) a mask of the locations for which the ground‐level elevation matches the pressure measured by the geolocator and (2) a mismatch between the temporal time series measured by the geolocator and the reanalysis dataset. This new method is introduced step by step and applied to 16 tracks of nine long‐ and short‐distance migrant species.Using known positions of double‐tagged individuals (light and pressure data), we demonstrate that our method is almost three times more accurate than light‐based positioning with an average error of 44 km in our trials. In contrast to the traditional light‐based approach, pressure geolocation can provide useful information for short stationary periods (less than a day) and is not affected by the equinox problem nor by any shading effects due to weather or animal behaviour. To facilitate the application of the method, we developed an R package GeoPressureR, together with a user guide GeopressureManual and starting code GeoPressureTemplate.The use of pressure sensors to position animals has the potential to become widespread thanks to the combination of both affordable lightweight devices (<0.4 g) and this method to estimate position of the device precisely and accurately. In particular, such devices can now be applied to short‐distant migrants (>100 km), forest‐dwelling species, nocturnal animals and altitudinal migrants. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate changes in the thermoregulatory mechanisms of juvenile yellowfin tuna, Thunnus albacares, with increasing body size by using archival tag data from 28 fish released in Japanese waters (fork length [FL] 35–92 cm). Fish with a body size of 35 cm FL remaining within the surface waters had lower thermal excess (0.4 °C), and fish with a body size of 40–60 cm FL undertaking brief diving at depths > 100 m had higher thermal excess (0.5–1.0 °C). However, the thermal excess did not consistently increase with body size, as has been reported for bigeye tuna. Heat budget models indicated inconsistent trends of decreased or increased heat production with body size. Yellowfin tuna regulate body temperatures by controlling the whole-body heat-transfer coefficient (λ) by 1.2–2.0 fold during descents and ascents, independent of body size, restricting λ for thermo-conservation during descent and increasing λ to absorb ambient heat during ascent. Compared with bigeye tuna, the vertical distributions of juvenile yellowfin tuna were limited to surface waters because of less efficient physiological thermoregulatory mechanisms. However, deep dives exceeding 1000 m, probably for predator avoidance, accompanied by rest in surface waters to recover from unusually higher behavioral activity, and vertical behavior similar to bigeye tuna “characteristic behavior” were observed. Compared to the thermoregulatory mechanisms of other tunas, those of juvenile yellowfin tuna are considered to be adaptive to tropical and subtropical shallower waters. [ABSTRACT FROM AUTHOR]

Abstract Background Archival tags that measure the Earth’s magnetic field could provide a new geolocation method for demersal fishes in the North Pacific Ocean. However, the presence of local magnetic field anomalies caused by geological formations such as volcanic rock and temporal fluctuations from solar storms could complicate its use in some high-latitude areas of the North Pacific Ocean. We assessed the potential value of adding geomagnetic data to a depth-based state-space model for geolocation of demersal fishes in Glacier Bay National Park, USA, a high-latitude magnetic anomaly area. We developed a high-resolution (100 m) magnetic field map of the study area and assessed in situ tag resolution by deploying 5 geomagnetic archival tags on a stationary mooring for 8 months. We compared performance of 4 theoretical geomagnetic tag measurement resolutions (low = ± 1000 nT, medium = ± 500 nT, high = ± 300 nT, and very high = ± 150 nT), 2 map resolutions (coarse- or fine-scale), and 5 methods of geomagnetic variance specification by estimating locations of simulated random walk trajectories under the different treatment scenarios using a hidden Markov model. Results Geomagnetic data improved model performance for both fine-scale and coarse-scale magnetic maps when tag resolutions were medium to very high and geomagnetic variance specification was based on error between measured and mapped values instead of study area attributes such as slope or roughness. Overall, the best model performance was observed for the highest tag resolution, the fine-scale map, and variance based on anomaly magnitudes. However, the coarse-scale map with a constant variance of 165 nT resulted in improvements over depth alone for all tag resolutions. In situ testing of mooring data suggests that the precision of the geomagnetic archival tags was comparable to the low and medium tag measurement resolutions tested in simulations, but variation in performance was high among tags. Conclusions Our results suggest that inclusion of geomagnetic data could improve geolocation of demersal fishes in the North Pacific Ocean, but improvements to geomagnetic tags and additional information on magnetic field values measured at the seafloor compared to the sea surface are needed to ensure its utility.

A total of 1522 yellowfin tuna, Thunnus albacares, were captured, tagged, and released with surgically implanted archival tags (ATs), in six discrete areas of the eastern and central Pacific Ocean, during 2002 through 2019. Of 483 ATs returned (31.7%), 227 ATs from yellowfin (48–147 cm in fork length) at liberty from 32 to 1846 d (x¯ = 300.1 d) provided suitable data sets which were processed using an unscented Kalman filter model with sea‐surface temperature measurements integrated (UKFsst) in order to obtain most probable tracks and movement parameters. Although some differences were observed in the movement patterns for fish from within and among the six release areas, 99% of the 227 fish remained within 1000 M of their release locations, indicating limited dispersion and fidelity to release locations. The median movement parameter D, which defines dispersion from the UKFsst model, for the fish released in the offshore equatorial areas showed much greater dispersion rates compared to those for the fish released along the coast or around islands. The rates of mixing of yellowfin among the release areas were found to be dependent on the distances between release areas, with, in general, the greatest mixing occurring among areas in closest proximity, whereas for the two areas offshore Mexico and the two offshore equatorial areas, the rates of mixing were nonexistent or negligible. [ABSTRACT FROM AUTHOR]

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The yellowfin tuna (Thunnus albacares: YFT) is a widely distributed, migratory species that supports valuable commercial fisheries. Landings of YFT are seasonally and spatially variable, reflecting changes in their availability and accessibility to different fleets and metiers which, in turn, has implications for sustainable management. Understanding the dynamics of YFT behaviour and how it is affected by biological and ecological factors is therefore of consequence to fisheries management design. Archival and pop-up satellite tags (PSAT) were used in the South Atlantic Ocean around St Helena between 2015 and 2020 to collect information on the movements, foraging and locomotory behaviour of YFT. The study aimed to (1) identify vertical behaviour of YFT within St Helena’s EEZ; (2) assess the timing and depth of potential feeding events and (3) to use the information to inform on the catchability of YFT to the local pole and line fishing fleet. Results indicate that the YFT daytime behaviour shifted between shallow with high incidence of fast starts in surface waters in summer months (December to April), to deep with high incidence of strikes at depth in colder months (May to November). Catchability of YFT was significantly reduced between May and November as YFT spent more time at depths below 100 m during the day, which coincides with a reduction in the quantity of YFT caught by the inshore fleet.

Changes in the thermoregulatory mechanisms of juvenile bigeye tuna (Thunnus obesus) as body size increases were investigated by comparing associative (fish associated with floating objects) and characteristic (non‐associative) behaviors using archival tag data from 15 fish released in Japanese waters [49–72 cm fork length (FL) at release, 3–503 days]. The thermal excess (body temperature minus ambient temperature) during characteristic behavior was about 0.7–2.3°C higher than that during associative behavior in equally sized fish, and both increased with body size. Heat budget models indicated that the increases in the thermal excess of both behaviors could be attributed to decreases in the whole‐body heat transfer coefficient (λ) while descending. Thermoregulatory mechanisms appear to develop with body size by controlling λ during descents and ascents, especially in characteristic behavior (associative: 50 cm FL, 2.6‐fold; 95 cm FL, 6.4‐fold; characteristic: 55 cm FL, 5.5‐fold; 95 cm FL, 15.8‐fold). The λ increases while ascending to allow rapid body temperature recovery by absorbing the ambient heat in warmer, shallower water and is restricted for thermoconservation while descending to deeper, cooler water. The heat production results and calculated body temperatures for both behaviors suggest that associative behavior is the inactive state, so physiological thermoregulatory energy may be less necessary than during characteristic behavior. As body bulk λ decreased with body size, it appears that physiological thermoregulation, by controlling arterial blood flow and/or vasoconstriction, develops to adapt to deeper, offshore waters for better exploitation of prey, in turn supporting the increasing energy demands of larger fish. [ABSTRACT FROM AUTHOR]

Cobia (Rachycentron canadum) is a large coastal pelagic fish species that represents an important fishery in many coastal Atlantic states of the U.S. They are heavily fished in Virginia when they migrate into Chesapeake Bay during the summer to spawn and feed. These coastal habitats have been subjected to warming and increased hypoxia which in turn could impact the timing of migration and the habitat suitability of Chesapeake Bay. With conditions expected to worsen, we project current and future habitat suitability of Chesapeake Bay for cobia and predict changes in their arrival and departure times as conditions shift. To do this we developed a depth integrated habitat model from archival tagging and physiology data from cobia that used Chesapeake Bay, and applied the model to contemporary and future temperature and oxygen output from a coupled hydrodynamic-biogeochemical model of Chesapeake Bay. We found that estimated arrival occurs earlier and estimated departure time occurs later when temperatures are warmer and that by mid- and end-of-century cobia may spend on average up to 30 and 65 more days, respectively, in Chesapeake Bay. By mid-century we do not expect habitat suitability to change substantially for cobia, but by end-of-century we project it will significantly decline and shift closer to the mouth of Chesapeake Bay. Our study provides evidence that cobia will have the capacity to withstand near term impacts of climate change, but that their migration phenology varies from year to year with changing temperatures. These findings emphasize the need to incorporate the relationship between fishes and their environment into how fisheries are managed. This information can also help guide managers when deciding the timing and allocation of a fishery.

Abstract Large scale migrations are a key component of the life history of many marine species. We quantified the annual migration cycle of juvenile southern bluefin tuna (Thunnus maccoyii; SBT) and spatiotemporal variability in this cycle, based on a multi-decadal electronic tagging dataset. Behaviour-switching models allowed for the identification of cohesive areas of residency and classified the temporal sequence of movements within a migration cycle from austral summer foraging grounds in the Great Australian Bight (GAB) to winter foraging grounds in the Indian Ocean and Tasman Sea and back to the GAB. Although specific regions within the Indian Ocean were frequented, individuals did not always return to the same area in consecutive years. Outward migrations from the GAB were typically longer than return migrations back to the GAB. The timing of individual arrivals to the GAB, which may be driven by seasonality in prey availability, was more cohesive than the timing of departures from the GAB, which may be subject to the physiological condition of SBT. A valuable fishery for SBT operates in the GAB, as do a number of scientific research programs designed to monitor SBT for management purposes; thus, understanding SBT migration to and from the area is of high importance to a number of stakeholders.

Abstract Background Knowledge of the complete horizontal migration and vertical movements of Atlantic salmon (Salmo salar L.) during the marine phase is important for understanding the link between individual processes and population recruitment. We studied the detailed migration behaviour of six post-spawned adult Atlantic salmon from a North Norwegian river, during the entire ocean migration, by using high-resolution light-based geolocation archival tags. Results The fish performed long-distance migrations and utilized Arctic areas from the eastern Barents Sea, to areas of Jan Mayen Island, and north to Svalbard. Four of six individuals exhibited a strong fidelity towards Jan Mayen Island, particularly during winter, which may suggest that the ecological conditions in these waters may be important for overwintering. One fish displayed exclusive utilization of the Barents Sea, indicating that growth and survival of some individuals are entirely dependent on these waters. The fish displayed a pelagic behaviour and all individuals spent more than 83% of the time in the uppermost 10 m of the water column. There was a strong seasonal trend in diving intensity, with the number of dives increasing with day length, independent of individuals’ spatial distribution. Diving depth was positively correlated with the depth of the mixed layer. Conclusions The Atlantic salmon displayed large individual variation in horizontal migrations, utilizing different ocean areas north of the Arctic Circle. This means that, despite the overall fidelity towards northern latitudes, individuals from the same population may experience highly different ecological conditions, potentially contributing to within-population variation in growth and survival. The seasonal correlation between diving intensity and day length, and spatial correlation between diving depth and depth of the mixed layer, indicate that the overall depth use of the Atlantic salmon depends on both spatially independent seasonal factors, and dynamic oceanographic conditions that facilitate food aggregations. This is the first study of Atlantic salmon to present detailed information about individuals’ continuous horizontal migration and simultaneous vertical movements during the entire ocean migration, thus providing novel information on how habitat use change throughout the ocean residency.

Aim: Climate change has influenced the distribution and phenology of marine species, globally. However, knowledge of the impacts of climate change is lacking for many species that support valuable recreational fisheries. Cobia (Rachycentron canadum) are the target of an important recreational fishery along the U.S. east coast that is currently the subject of a management controversy regarding allocation and stock structure. Further, the current and probable future distributions of this migratory species are unclear, further complicating decision‐making. The objectives of this study are to better define the contemporary distribution of cobia along the U.S. east coast and to project potential shifts in distribution and phenology under future climate change scenarios. Location: Chesapeake Bay and the U.S. east coast. Methods: We developed a depth‐integrated habitat suitability model using archival tagging data from cobia that were caught and tagged in Chesapeake Bay during summer months and coupled those data with high‐resolution ocean models to project the contemporary and future distributions of cobia along U.S. east coast. Results: During the winter months, suitable cobia habitat currently occurs in offshore waters off North Carolina and further south, whereas during the summer months, suitable habitat occurs in waters from Florida to southern New England. In warmer years, the availability of suitable habitat increases in northern latitudes. Under continued climate change over the next 40–80 years, suitable habitat is projected to shift northward and decrease over the shelf. Main conclusions: Habitat distributions suggest cobia overwinter offshore and could inhabit waters further north during warmer months, into state jurisdictions that do not have strict management regulations for cobia. When waters are warmer, distributions are projected to shift poleward and seasonal migrations may begin earlier. These results can inform resource allocation discussions between fishery managers and resource users. [ABSTRACT FROM AUTHOR]

Background: Archival tags that measure the Earth's magnetic field could provide a new geolocation method for demersal fishes in the North Pacific Ocean. However, the presence of local magnetic field anomalies caused by geological formations such as volcanic rock and temporal fluctuations from solar storms could complicate its use in some high-latitude areas of the North Pacific Ocean. We assessed the potential value of adding geomagnetic data to a depth-based state-space model for geolocation of demersal fishes in Glacier Bay National Park, USA, a high-latitude magnetic anomaly area. We developed a high-resolution (100 m) magnetic field map of the study area and assessed in situ tag resolution by deploying 5 geomagnetic archival tags on a stationary mooring for 8 months. We compared performance of 4 theoretical geomagnetic tag measurement resolutions (low = ± 1000 nT, medium = ± 500 nT, high = ± 300 nT, and very high = ± 150 nT), 2 map resolutions (coarse- or fine-scale), and 5 methods of geomagnetic variance specification by estimating locations of simulated random walk trajectories under the different treatment scenarios using a hidden Markov model. Results: Geomagnetic data improved model performance for both fine-scale and coarse-scale magnetic maps when tag resolutions were medium to very high and geomagnetic variance specification was based on error between measured and mapped values instead of study area attributes such as slope or roughness. Overall, the best model performance was observed for the highest tag resolution, the fine-scale map, and variance based on anomaly magnitudes. However, the coarse-scale map with a constant variance of 165 nT resulted in improvements over depth alone for all tag resolutions. In situ testing of mooring data suggests that the precision of the geomagnetic archival tags was comparable to the low and medium tag measurement resolutions tested in simulations, but variation in performance was high among tags. Conclusions: Our results suggest that inclusion of geomagnetic data could improve geolocation of demersal fishes in the North Pacific Ocean, but improvements to geomagnetic tags and additional information on magnetic field values measured at the seafloor compared to the sea surface are needed to ensure its utility. [ABSTRACT FROM AUTHOR]

Artificial structures in the marine environment may have direct and/or indirect impact on the behaviour and space use of mobile foragers. This study explores whether environmental and physical features in the North Sea—including artificial structures (wrecks, wind turbines, cables, and oil and gas structures) were associated with local abundance of three fish species: cod (Gadus morhua), plaice (Pleuronectes platessa), and thornback ray (Raja clavata). Generalized additive models (GAMs) were used to compare distributions between data collected by fisheries surveys and electronic tags. Distributions of cod, plaice, and ray were correlated with environmental variables including temperature, depth, and substrate, matching findings from previous studies. All species showed seasonal increases in their abundance in areas with high densities of artificial structures, including oil and gas platforms and wrecks. Independent of whether fish purposefully associate with these features or whether structures happen to coincide with locations frequented by these populations, the strong association suggests that greater consideration needs to be given to regulation of habitat alterations, including decommissioning. [ABSTRACT FROM AUTHOR]

Warming water temperatures present challenges for ectotherms in freshwater ecosystems through influence on metabolic rate and bioenergetics. Diet, such as the inclusion of high energy prey, can reduce these influences, but accurate temperature profiles are key to improved predictions. Here, using the Wisconsin bioenergetics approach, we modelled lake trout (Salvelinus namaycush) and Chinook salmon (Oncorhynchus tshawytscha) growth for two time periods (present [2010–2019] and future 30-year (2041–2070) averaged scenarios) in Lake Ontario with in-situ observed year-round temperatures (obtained through acoustic telemetry and pop-off data storage tags deployed between 2016 and 2019) occupied by the species. For the future, we considered two water temperature scenarios (low and high, where experienced temperature increased by a mean of 0.4 °C and 1.0 °C, respectively) and the effects of a hypothetical diet switch with the inclusion of higher energy prey (bloater, Coregonus hoyi) currently being reintroduced. Under all forecasted warming conditions, lake trout performed well and growth was 41.3 to 82.5 % above present when bloater was re-incorporated in the diet up to 40 %. Chinook salmon maximum attainable growth declined between 11.2 and 29.6 % under forecasted warming scenarios without diet change. However, when bloater comprised ∼ 33 % of their diet, Chinook salmon growth increased 3.7 % under the low future scenario compared to present. These results demonstrate that impacts of future lake warming on predatory fish will vary with life-history characteristics of species and composition and abundance of prey base, and highlights the need for effective management that diversifies and conserves forage fish species in the Great Lakes. [ABSTRACT FROM AUTHOR]

Abstract In this commentary, we describe how geomagnetic intensity can be used to estimate latitude, discuss its strengths and weaknesses, and argue for its potential use along with irradiance measurements for estimating the latitude of a migratory fish carrying an archival tag. We conclude this commentary by suggesting that researchers and tag manufacturers estimate positions using as many inputs as possible, environmental irradiance, sea surface temperature, and geomagnetic field. Each environmental property will provide a better estimate of position at different times of the year and locations on earth. We contend that one geolocation estimation approach is not better than another, as each functions optimally under different circumstances and thus should be used accordingly.

We examine the dive and movement behavior of blue, fin, and humpback whales along the US West Coast in regions with high ship traffic where ship strikes have been identified as a major concern. All three species are known to feed in coastal waters near areas of high ship traffic. We analyzed data from 33 archival tag deployments representing over 3,000 h of data that were attached with suction-cups or short darts for periods >20 h and recorded depth (≥ 1 Hz), fast-lock GPS positions and other sensors. There were clear differences among the three species but all showed a distinct diurnal difference in diving behavior. While dive depth varied among animals based on where prey was located, whales spent a high proportion of their time closer to the surface where they would be more vulnerable to ship strikes at night than in the day. This was most pronounced for blue whales where vulnerability was twice as high at night compared to the day. We also found differences in movement patterns of whales between day and night. Movements were more localized to specific areas in the day near prey resources while at night these movements often involved directional movements (though sometimes returning to the same area). We show how in several specific areas like the Santa Barbara Channel, these differences in movements and locations translate to a very different overlap with shipping lanes at night compared to the daytime locations, which is the basis for most sighting data.

Tope (Galeorhinus galeus) is a highly mobile elasmobranch in the temperate to subtropical northeast Atlantic. It is highly migratory and has been shown to display complex movement patterns, such as partial migration, in the southern hemisphere. In the northeast Atlantic, previous mark-recapture studies have struggled to identify movement patterns and the species behavior is poorly described, yet identification of migratory behaviors and habitats of importance for the species is of paramount importance for effective management. Here, we combined fisheries independent survey data with mark-recapture (MR) data to investigate the distribution of different age classes of tope across the northeast Atlantic. We further investigated depth use in detail with archival electronic tags and a pop-up satellite archival tag (PSAT). We suggest previous studies struggling to find consistent movement patterns using MR data were confounded by a combination of site fidelity, partial migration by females, and increasing depth and home range of juveniles. Survey and MR data showed immature tope

Knowledge of patterns and drivers of the spatiotemporal distribution of top predatory fish is key to understand ecological dynamics and to successful management. Here, we integrated field and laboratory approaches to study vertical movements of pike (Esox lucius) in relation to season, light regimes and body temperature. We tagged pike from the Baltic Sea with data storage tags during spawning migration and retrieved them during migration the following years to obtain high‐resolution data from full year of movements. The results showed seasonal and diel patterns of activity and body temperature that conformed to distinct patterns of crepuscular activity and diel vertical migrations. The latter manifested as two different patterns, either a stationary phase in the surface water during day followed by night‐time in deeper water or vice versa. The occurrence of these two behaviours varied among individuals and within individuals among seasons. Diel vertical migration has previously not been described for this shallow‐dwelling species, but was a common and consistent behaviour among individuals in this study. We suggest that the function of the daytime surface behaviour in pike is to increase body temperature through sun basking. This thermoregulatory role of surfacing was supported by the laboratory study where individuals sought the surface layer, exposed themselves to infrared light and thereby attained body temperatures in excess of ambient water. These results support sun basking as a mechanism for heat gain and further suggest that access to sunlight in the surface layer could be an important driver of vertical migrations. [ABSTRACT FROM AUTHOR]

Light‐level geolocator tags use ambient light recordings to estimate the whereabouts of an individual over the time it carried the device. Over the past decade, these tags have emerged as an important tool and have been used extensively for tracking animal migrations, most commonly small birds.Analysing geolocator data can be daunting to new and experienced scientists alike. Over the past decades, several methods with fundamental differences in the analytical approach have been developed to cope with the various caveats and the often complicated data.Here, we explain the concepts behind the analyses of geolocator data and provide a practical guide for the common steps encompassing most analyses – annotation of twilights, calibration, estimating and refining locations, and extraction of movement patterns – describing good practices and common pitfalls for each step.We discuss criteria for deciding whether or not geolocators can answer proposed research questions, provide guidance in choosing an appropriate analysis method and introduce key features of the newest open‐source analysis tools.We provide advice for how to interpret and report results, highlighting parameters that should be reported in publications and included in data archiving.Finally, we introduce a comprehensive supplementary online manual that applies the concepts to several datasets, demonstrates the use of open‐source analysis tools with step‐by‐step instructions and code and details our recommendations for interpreting, reporting and archiving. [ABSTRACT FROM AUTHOR]

Vertical movements related to the thermoregulation were investigated in 12 juvenile bigeye tuna (Thunnus obesus) in Japanese waters using archival tag data. Movements changed with time of day, season, and body size. During daytime, bigeye tuna descended to greater depths, presumably to feed in the deep scattering layer (DSL). Thereafter, they repeatedly ascended to shallower layers, suggesting attempts at behavioral thermoregulation, although the beginning of vertical thermoregulatory ascents might reflect a shift in DSL depth. By the end of such movement, the whole‐body heat‐transfer coefficient might decrease because, although the depth and ambient temperature of the upper layers did not change, the body temperature gradually decreased significantly just after ascent for thermoregulation. Seasonal patterns indicated that the vertical thermal structure of the ocean might influence this ascent behavior. For example, from January to May, bigeye tuna made fewer ascents to less shallow waters, suggesting that they respond to increasing depths of the mixed surface layer by reducing energy expenditure during vertical migration. In addition, as body size increased, fewer thermoregulatory ascents were required to maintain body temperature, and fish remained deeper for longer periods. Thus, vertical thermoregulatory movements might change with body size as bigeye tuna develop better endothermic and thermoregulatory abilities. We hypothesize that bigeye might also increase cold tolerance as they grow, possibly due to ontogenetic shifts in cardiac function. [ABSTRACT FROM AUTHOR]

• We adapted a Hidden Markov Model (HMM) for geolocation of demersal fishes in the North Pacific Ocean. • Parameterization choices affect model performance in study areas with heterogeneous bathymetry. • When model assumptions are not valid, accuracy decreases and location error may be underestimated. • Study area heterogeneity should be considered when choosing grid size and data likelihood models. • Customizing the HMM for different applications is important for performance and interpreting results. State-space geolocation models can provide valuable information on the large-scale movements of many fish species. The sensitivity of such complex models to model assumptions and fixed parameters is rarely assessed quantitatively, yet is important for interpretation of results and adaptation for new species and different geographic regions. We hypothesized that parameterization and performance of a discrete Hidden Markov Model (HMM) with a Gaussian depth-based data likelihood for demersal fishes first implemented in the flat terrain of the North Sea would be affected by the more heterogeneous depths found in the North Pacific Ocean. We ran the HMM on depth data from simulated random walk movement trajectories in flat, sloping, and heterogeneous study areas in the North Pacific Ocean where known depth distributions in each model grid cell were provided by high-resolution (5 m) multibeam bathymetry data. Performance was compared among different data likelihood specifications and grid sizes in each area. We found that model performance decreased when grid cell depth distributions departed from normal distributions. Performance decreased with increasing grid size in the heterogeneous and sloping study areas but not the flat study area. A new method for specifying grid cell depth variance based on study area slope performed better than the standard method of obtaining variance from adjacent grid cell values for larger grid sizes in heterogeneous and sloping areas. Overall model performance was highest in the heterogeneous and sloping areas at small grid sizes and in the flat area at large grid sizes. The estimated value of diffusion was also sensitive to bathymetric heterogeneity and variance-specification method. These results suggest that the degree of study area heterogeneity should be considered when choosing fixed parameters such as likelihood and grid size, and when interpreting the model results. In addition, this approach demonstrates the need for sensitivity analyses when using the model on a new species and in a new study area. [ABSTRACT FROM AUTHOR]

Abstract Large numbers of juvenile southern bluefin tuna (SBT; Thunnus maccoyii) migrate into the warm shelf waters of the Great Australian Bight (GAB) each austral summer. Whilst in the GAB, they aggregate in schools that spend substantial periods in the surface layer of the water column. In this study we investigate biological, temporal and environmental factors influencing this surfacing phenomena using an extensive archival tagging dataset collected between 1998 and 2011. High frequency data on the vertical movement of SBT collected by these tags were used to calculate the proportion of time fish spent in the shallowest 20 m during each day and night period. Estimates of fish location derived from light sensor data on the tags allowed us to investigate the influence that local environmental conditions had on a fish's surfacing behaviour. Although there is high variability in surfacing behaviour within and between individuals, some general patterns emerge. There are clear diel differences in surfacing, with the proportion of time fish spend at the surface tending to be high during most days and either very high (>90%) or very low (<10%) during most nights. Complex relationships were found between surfacing behaviour and the environmental variables considered (sea surface temperature, chlorophyll, salinity and wind speed). The results from this study have relevance to the commercial purse-seine fishery targeting surface schools of SBT in the GAB during the austral summer, as well as the scientific aerial survey conducted each summer that collects data on sightings of surface schools of SBT in order to derive a relative abundance index used directly in management. [ABSTRACT FROM AUTHOR]

The sablefish (Anoplopoma fimbria) is a long-lived species with wide distribution throughout the North Pacific Ocean. While adult sablefish are considered a deepwater fish, diet analyses suggest that they undergo vertical migrations that could be related to prey movement and feeding. Pop-up satellite archival tags (PSATs) were used to observe the fine-scale depth selection behavior of adult sablefish tagged off the Washington coast during the summer from June to August. Tags were physically retrieved after they surfaced using direction-finding equipment so that complete datasets over the entire deployment were obtained from 14 tags. PSATs that recorded depth and temperature every 4 min during the deployment confirm that sablefish inhabit depths of 750 m or greater. However, a majority of the tagged fish underwent extensive vertical migrations that averaged 254.4 m overall and occurred at a 24 hr periodicity. Variations were observed among individuals in the amount of the deployment during which vertical migrations occurred, ranging from 12.37% to 63.48% of the time. During the vertical migration, fish ascended towards the surface at night and descended prior to daylight (i.e., diel vertical migration). Sablefish generally inhabited temperatures of 5°C but during the vertical migrations were found at temperatures from 6 to 10°C. Sablefish are opportunistic feeders with a large proportion of their diet being fish, euphausiids and cephalopods. Because these prey items also exhibit diel vertical migrations, it is possible that the vertical migratory behavior displayed by the sablefish was in response to the movements or the location of their prey. [ABSTRACT FROM AUTHOR]

Archival tagging studies of southern bluefin tuna ( SBT , Thunnus maccoyii) have revealed that juveniles residing in the Great Australian Bight ( GAB) over the austral summer undertake seasonal cyclic migrations to the southeast Indian Ocean and the Tasman Sea during winter. However, there remains disagreement about the extent of mixing between juvenile SBT regularly caught by longline fleets south of Africa and those observed in the GAB. Some researchers have argued that archival tag recoveries indicate most juveniles reside in the GAB over the austral summer. Others have suggested that recoveries of conventional and archival tags are better explained by a juvenile population consisting of separate groups on the eastern and western sides of the Indian Ocean with limited intermixing. We present analyses of catch and tag recovery data and re-examine archival tagging studies. The evidence provided strongly favors the hypothesis of separate juvenile subgroups, or contingents, with limited intermixing. We draw some tentative conclusions about the nature of the putative contingents and discuss some implications of these findings for the interpretation of existing datasets and future research priorities. We also provide the first evidence that the migration choices of juveniles that summer in the GAB are influenced by fidelity to winter feeding grounds and suggest this helps explain the collapse of the surface fishery off New South Wales in the 1980s. [ABSTRACT FROM AUTHOR]

In this commentary, we describe how geomagnetic intensity can be used to estimate latitude, discuss its strengths and weaknesses, and argue for its potential use along with irradiance measurements for estimating the latitude of a migratory fish carrying an archival tag. We conclude this commentary by suggesting that researchers and tag manufacturers estimate positions using as many inputs as possible, environmental irradiance, sea surface temperature, and geomagnetic field. Each environmental property will provide a better estimate of position at different times of the year and locations on earth. We contend that one geolocation estimation approach is not better than another, as each functions optimally under different circumstances and thus should be used accordingly. [ABSTRACT FROM AUTHOR]

We investigated the habitat utilization, vertical and horizontal behaviour of Atlantic bluefin tuna Thunnus thynnus (ABFT) in relation to oceanographic conditions in the northwestern Mediterranean Sea, based on 36 pop-up archival tags and different environmental data sets. Tags were deployed on early mature ABFT (127–255 cm) between July and November in 2007-2014, on the shelf area off Marseille, France. The data obtained from these tags provided 1643 daily summaries of ABFT vertical behaviour over 8 years of tag deployment. Based on a hierarchical clustering of this data, we could identify four principle daily vertical behaviour types, representing surface ( ≦ 10 m ) and subsurface (10–100 m) orientation, moderate (50–200 m) and deep ( ≧ 200 m ) diving behaviour. These vertical behaviour types showed seasonal variations with partly opposing trends in their frequencies. Accordingly, ABFT were more surface orientated during summer, while moderate diving behaviour was more common during winter. Depth time series data further revealed inverted day-night patterns for both of these periods. Tagged ABFT frequented the surface waters more regularly during daytime and deeper waters during the night in summer, while the opposite pattern was found in winter. Seasonal changes in the vertical behaviour of ABFT were accompanied by simultaneous changes in environmental conditions (SST, chla, thermal stratification). Accordingly, surface orientation and moderate diving behaviour appeared to be triggered by the thermal stratification of the water column, though less pronounced than previously reported for ABFT in the North Atlantic, probably indicating adaptive vertical behaviour related to the availability of epipelagic food resources (anchovies and sardines). Deep diving behaviour was particularly frequent during months of high biological productivity (February-May), although one recovered tag showed periodic and unusual long spike dives during summer-autumn, in relation to thermal fronts. Regional effects on the vertical behaviour of ABFT were identified through GAMs, with surface orientation being particularly pronounced in the Gulf of Lions, highlighting its suitability for an ongoing annual aerial survey program to estimate ABFT abundance in this region. In addition, increased levels of mesoscale activity/productivity (e.g. related to oceanic fronts) were detected in an area regularly utilized by ABFT, south of the Gulf of Lions, underlining its attractiveness as foraging ground. Kernel densities of geolocation estimates showed a seasonal shift in the horizontal distribution of ABFT from this “high-use” area towards the Gulf of Lions during summer, probably linked to the enhanced availability of epipelagic food resources at this time. [ABSTRACT FROM AUTHOR]

Information on lake sturgeon (Acipenser fulvescens) depth and thermal habitat use during non-spawning periods is unavailable due to the difficulty of observing lake sturgeon away from shallow water spawning sites. In 2002 and 2003, lake sturgeon captured in commercial trap nets near Sarnia, Ontario were implanted with archival tags and released back into southern Lake Huron. Five of the 40 tagged individuals were recaptured and were at large for 32, 57, 286, 301, and 880 days. Temperatures and depths recorded by archival tags ranged from 0 to 23.5 ºC and 0.1 to 42.4 m, respectively. For the three lake sturgeon that were at large for over 200 days, temperatures occupied emulated seasonal fluctuations. Two of these fish occupied deeper waters during winter than summer while the other occupied similar depths during non-spawning periods. This study provides important insight into depth and thermal habitat use of lake sturgeon throughout the calendar year along with exploring the feasibility of using archival tags to obtain important physical habitat attributes during non-spawning periods. [ABSTRACT FROM PUBLISHER]

Lumpfish (Cyclopterus lumpus) is a high latitude species most abundant in Arctic and sub-Arctic waters of the North Atlantic. Vertical behaviour of this fish is unclear as it is often caught by both pelagic and demersal trawls. To gain greater insight into its behaviour, 41 female lumpfish caught during the Icelandic Groundfish Survey (IGFS) in March were tagged with data storage tags (DSTs); the IGFS finishes ~1 week before the beginning of the lumpfish fishing season (20 March). Data retrieved from returned tags were compared with information on depth and distribution of catches of lumpfish from the IGFS. Thirteen tags were returned with days at liberty ranging from 20 to 61 d. Maximum depth recorded was 308 m (maximum depth of the tag) but based upon interpolation of temperature recordings, one fish may have descended to ~418 m. Lumpfish displayed a range of vertical behaviours termed demersal, surface, and pelagic. During March, most exhibited either demersal or pelagic behaviour but the time spent in surface behaviour increased from March to April. During demersal behaviour, depth was rarely constant indicating the fish were not stationary. Both DST and catch data from the IGFS indicate that lumpfish exhibit diel patterns in vertical behaviour. As lumpfish frequently exhibit demersal behaviour, the use of the IGFS to monitor changes in abundance is justified. As lumpfish spend a significant amount of time in both the pelagic and demersal zone, they should be considered as a semi-pelagic (or semi-demersal) fish during this life stage/time of year. [ABSTRACT FROM AUTHOR]

8217 days of data downloaded from 47 archival tags, recovered from bigeye tuna ( Thunnus obesus ) 51–134 cm in length ( x ¯ = 86.9 c m ) , 0.87–3.44 years of age ( x ¯ = 1.89 years ) at liberty from 36 to 851 days ( x ¯ = 183 days ) in the equatorial central Pacific Ocean, are evaluated herein. Analyses of depth and temperature records resulted in the classification of three daily behavior types: characteristic, associative (associated with floating objects), and other. For three defined length classes, 54–79.9 cm, 80–99.9 cm, and 100–134 cm, when exhibiting characteristic behavior, the proportions of time and average durations of events were 45.3% ( x ¯ = 5.1 days ) , 62.6% ( x ¯ = 8.5 days ) , 79.2% ( x ¯ = 17.5 days ) , and the average daytime depths and temperatures were 284 m and 12.6 °C, 305 m and 12.7 °C, and 312 m and 12.1 °C, respectively. For the same three length classes, when exhibiting associative behavior, the proportions of time and average durations of events were 9.5% ( x ¯ = 1.9 days ) , 4.8% ( x ¯ = 1.9 days ) , and 6.0% ( x ¯ = 1.8 days ) , and the average daytime depths and temperatures were 101 m and 23.2 °C, 105 m and 23.1 °C, and 74 m and 22.3 °C, respectively. There is a significant positive correlation between the proportion of time fish exhibits characteristic behavior and fish length, and significant negative correlations between the proportion of time bigeye tuna exhibit associative and other behavior with fish length. Behavior and habitat preferences of bigeye tuna should be considered for standardizing catch-per-unit of effort (CPUE) data from both longline and purse-seine fisheries targeting tropical tunas in the Pacific, in an effort to provide more reliable estimates of relative abundance. [ABSTRACT FROM AUTHOR]

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The growth equation currently used for Atlantic bluefin tuna, Thunnus thynnus (L.), eastern stock (Lt = 318.85 [1-e-0.093 (t + 0.97)]) is validated using several approaches. The first method involved a comparison of studies with von Bertalanffy parameter estimates in which, different methods for the age estimation are utilized, taking as references the maximum size of this species (Lmax = 319.93 ± 11.3 cm) and the growth equation of the western Atlantic stock (Lt = 314.90 [1-e-0.089 (t + 1.13)]). The result of this analysis showed that the growth equation used by ICCAT's Standing Committee on Research and Statistics Atlantic bluefin tuna assessment group for the eastern stock perfectly fits Lmax. Second, an analysis was realized from first dorsal spine rings, 578 samples (age groups 0 to 3) of ABFT collected from the Bay of Biscay and the Mediterranean Sea, enabled the interpretation of the wide opaque bands (fast growth), formed during the boreal late spring and completed by autumn (June to November), and the translucent rings (hyaline rings, slow growth), formed during boreal autumn to late spring (November to May-June). In addition, first dorsal spine sections bands of two recovered fish that had carried conventional and electronic archival tags are also consistent. The chronological analysis of the opaque bands and hyaline rings of one fish tagged with an archival tag and recovered in the Bay of Biscay (the first time such a spine had been available for such analysis) revealed that transatlantic migrations may lead to double hyaline ring formation in the spine. Finally, the validation of the ABFT growth equation is made by superimposing tag-recovery data from tagging surveys in the Bay of Biscay, western Mediterranean and western Atlantic (N = 131) and spine readings (N = 299) to the eastern stock ABFT growth equation and analysing residuals. The coefficient of determination (R² = 97.98) and the residual's distribution indicated good performance of the model. Although no important differences between the growth model of the eastern stock and that of the western stock are found, in all cases studied, the predictive accuracy indicators are better for the eastern model. [ABSTRACT FROM AUTHOR]

Three analytical tools including archival tags, stable isotope analysis, and bioenergetics modeling were applied to two strains of rainbow trout Oncorhynchus mykiss in the Minnesota waters of Lake Superior to determine habitat and trophic position. Between 2006 and 2009, archival tags that recorded time, temperature, and pressure were surgically implanted into the peritoneal cavities of 34 steelhead ("SIT') and 93 Kamloops ("KAM") which were released into Lake Superior. After the initial spawning season, 10 STT and 9 KAMtags were recovered, with up to two years of recorded data. Both strains were surface-oriented, spending more than half of their time as adults in the top 1 m of water, and 80% of their time in the top 2 m. Diel vertical movements were noted more often in STT, likely reflecting higher consumption of Mysis diluviana, while the frequencies of other vertical movement patterns were similar between the two strains. Mean temperatures recorded by tags were used in bioenergetics simulations to estimate consumption of prey species. Temperatures recorded by archival tags were warmer than the water temperatures used in earlier bioenergetics simulations in Minnesota waters, and estimated consump-tion of prey fish by STT and KAM populations at the warmer temperatures was about 23% greater. Stable isotope analyses reflected higher consumption of small fish by both predator strains than identified in prior diet summa-ries based on stomach contents. Based on these analyses, habitats occupied by both strains are similar, and their impact on prey fish populations in nearshore waters is greater than previously estimated. [ABSTRACT FROM AUTHOR]