Description: Ecosystem-based management is costly. Therefore, without rigorously showing that it can outperform traditional species-focused alternatives, its broad-scale adoption in conservation is unlikely. We present a large-scale replicated and controlled set of whole-lake experiments in fish conservation (20 lakes monitored over 6 years with more than 150,000 fish sampled) to examine the outcomes of ecosystem-based habitat enhancement (coarse woody habitat addition and shallow littoral zone creation) versus a widespread, species-focused alternative that has long dominated fisheries management practice (i.e., fish stocking). Adding coarse woody habitats alone did not, on average, enhance fish abundance, but creating shallow water habitat consistently did, especially for juvenile fish. Species-focused fish stocking completely failed. We provide strong evidence questioning the performance of species-focused conservation actions in aquatic ecosystems and instead recommend ecosystem-based management of key habitats.

Description: Acoustic telemetry is a popular and cost-efficient method for tracking the movements of animals in the aquatic ecosystem. But data acquired via acoustic telemetry often contains spurious detections that must be identified and excluded by researchers to ensure valid results. Such data management is difficult as the amount of data collected often surpasses the capabilities of simple spreadsheet applications. ATfiltR is an open-source package programmed in R that allows users to integrate all telemetry data collected into a single file, to conditionally attribute animal data and location data to detections and to filter spurious detections based on customizable rules. Such tool will likely be useful to new researchers in acoustic telemetry and enhance results reproducibility. • ATfiltR compiles telemetry files and identifies and stores all data that was collected outside of your study period (e.g. when your receivers were on land for servicing) elsewhere. • As spurious detections are unlikely to appear sequentially in the data, ATfiltR finds all detections that occurred only once (per receiver or in the whole array) within a user-designated time period and stores them elsewhere. • ATfiltR identifies detections that are impossible given the animals’ swimming speeds and the receivers detection range and stores them elsewhere.

Description: Many capture fisheries are considered data-poor, including the northern pike (Esox lucius) fishery in brackish lagoons in the southern Baltic Sea of Germany. The objective of our work was to assess the exploitation status of this stock, which is perceived by stakeholders to be in decline. Size structure data collected via rod-and-reelangling, fyke nets, and gill nets, and empirical estimates of growth, maturation, and fecundity from the lagoon stock were used to fit the Length-Based Spawning Potential Ratio (LB-SPR) model. Parameter uncertainty in von Bertalanffy growth estimates and natural mortality in the Baltic Sea pike stock was considered in sensitivity analyses. Assessment outcomes were sensitive to estimates of growth rate, particularly asymptotic length L infinity, instantaneous natural mortality M, and gear selectivity. Under-aging of old fish in scale-based age estimates overestimated terminal length and generated negative bias in the estimated stock status. Despite the sensitivity of assessment outcomes to life-history parameter choice, the stock status for the Baltic Sea consistently indicated a fully exploited situation with SPRs robustly above 0.4 and current fishing mortality rates between 0.2 and 0.4 yr-1. This result agreed with previous assessments using catch-only models. Our work serves as a reminder, that when using length-based methods, unbiased growth, and natural mortality estimates are critical for robust assessment outcomes.

Description: Coarse woody habitat (CWH) is an important structural habitat in freshwater ecosystems. In natural lakes, CWH accumulates over centuries alongside the succession of littoral tree communities. Newly created gravel pit lakes have difficulties in accumulating CWH due to their young age. Additionally, CWH presence might be negatively affected by shoreline development, where wood is removed to facilitate recreational activities such as angling. We studied 26 gravel pit lakes with an age ≤ 55 yrs in Lower Saxony, Germany, to quantify CWH density and to understand the impact of environmental factors, including lake morphology, lake age, wind direction, abundance of riparian trees, and the presence or absence of fisheries management, on CWH density. We sampled small and large CWH in the littoral zone of the study lakes using a transect-based approach. Density of CWH was lower in German gravel pit lakes than in North American natural lakes. In gravel pit lakes, we detected increasing densities of small CWH with increasing numbers of large trees on the shore and with increasing littoral slopes in lakes managed for recreational fisheries. Large CWH density was positively affected by lake age, by the density of large trees on the shore and with wind from land, and again by steep littoral slopes in lakes managed for recreational fisheries. We recommend that recreational fisheries managers and individual anglers maintain CWH in shallow littoral zones to promote fish habitats in generally low-structured gravel pit lakes.

Description: 1. Geolocating aquatic animals with acoustic tags has been ongoing for decades, relying on the detection of acoustic signals at multiple receivers with known positions to calculate a 2D or 3D position, and ultimately recreate the path of an aquatic animal from detections at fixed stations. 2. This method of underwater geolocation is evolving with new software and hardware options available to help investigators design studies and calculate positions using solvers based predominantly on time-difference-of-arrival and time-of-arrival. 3. We provide an overview of the considerations necessary to implement positioning in aquatic acoustic telemetry studies, including how to design arrays of receivers, test performance, synchronize receiver clocks and calculate positions from the detection data. We additionally present some common positioning algorithms, including both the free open-source solvers and the ‘black-box’ methods provided by some manufacturers for calculating positions. 4. This paper is the first to provide a comprehensive overview of methods and considerations for designing and implementing better positioning studies that will support users, and encourage further knowledge advances in aquatic systems.

Description: One of the most important tasks of ecology is to understand how animals use space and time. Recent advances in the development of automated telemetry systems have enabled tremendous progress in understanding animal ecology, distribution, and behavior in both terrestrial and aquatic environments [1,2,3]. The field of biotelemetry has shifted rapidly from data-poor to data-rich field, when new technologies started to provide huge amounts of data about tracked animals, with unprecedented temporal and spatial resolution [3]. However, these new tracking tools also bring many challenges that can be effectively mitigated only through international and interdisciplinary collaborative efforts. Such initiatives represent indispensable platforms for sharing data, ideas, and technical capacity, establishment of common protocols and standards, efforts to address research questions at broader scales, implementation of international and transdisciplinary research projects, and facilitated uptake of obtained knowledge and information to inform governance and policy [4, 5]. Data sharing is one of the major goals of collaborative research networks, because sharing provides a unique opportunity to upscale data to landscape or ecosystem scales, which is simply intractable for individual research groups to accomplish independently, given the costs and logistics of instrumenting multiple areas for replicated research. Archiving data according to FAIR principles [6] and allowing connections to be forged across research groups is essential for ecologists to leverage the power of acoustic tracking against the high direct and indirect costs of project implementation. There is a growing number of international networks for collecting and sharing telemetry data that operate around the world, including the Ocean Tracking Network (OTN), Integrated Marine Observing System (IMOS), European Tracking Network (ETN), Great Lakes Acoustic Observation System (GLATOS), Acoustic Tracking Array Platform (ATAP), and Lake Fish Telemetry Group (LFTG) [7,8,9,10,11]. The LFTG was established to advance topics in aquatic ecology using shared data sets, data systems, and ecosystem thinking. We present here a brief overview of the LFTG, as an example of an international and interdisciplinary network, with its positive features, challenges, and lessons learned. We further provide an overview of the thematic series ‘Advancing Movement Ecology Through Freshwater Fish Tracking’, which has been initiated through this network, and discuss key future challenges regarding data sharing within and among such networks.

Description: Foraging is a behavioural process and, therefore, individual behaviour and diet are theorized to covary. However, few comparisons of individual behaviour type and diet exist in the wild. We tested whether behaviour type and diet covary in a protected population of Atlantic cod, Gadus morhua. Working in a no-take marine reserve, we could collect data on natural behavioural variation and diet choice with minimal anthropogenic disturbance. We inferred behaviour using acoustic telemetry and diet from stable isotope compositions (expressed as δ13C and δ15N values). We further investigated whether behaviour and diet could have survival costs. We found cod with shorter diel vertical migration distances fed at higher trophic levels. Cod δ13C and δ15N values scaled positively with body size. Neither behaviour nor diet predicted survival, indicating phenotypic diversity is maintained without survival costs for cod in a protected ecosystem. The links between diet and diel vertical migration highlight that future work is needed to understand whether the shifts in this behaviour during environmental change (e.g. fishing or climate), could lead to trophic cascades.

Description: Background: Animals are expected to adjust their social behaviour to cope with challenges in their environment. Therefore, for fish populations in temperate regions with seasonal and daily environmental oscillations, characteristic rhythms of social relationships should be pronounced. To date, most research concerning fish social networks and biorhythms has occurred in artificial laboratory environments or over confined temporal scales of days to weeks. Little is known about the social networks of wild, freely roaming fish, including how seasonal and diurnal rhythms modulate social networks over the course of a full year. The advent of high-resolution acoustic telemetry enables us to quantify detailed social interactions in the wild over time-scales sufficient to examine seasonal rhythms at whole-ecosystems scales. Our objective was to explore the rhythms of social interactions in a social fish population at various time-scales over one full year in the wild by examining high-resolution snapshots of a dynamic social network. Methods: To that end, we tracked the behaviour of 36 adult common carp, Cyprinus carpio, in a 25 ha lake and constructed temporal social networks among individuals across various time-scales, where social interactions were defined by proximity. We compared the network structure to a temporally shuffled null model to examine the importance of social attraction, and checked for persistent characteristic groups over time. Results: The clustering within the carp social network tended to be more pronounced during daytime than nighttime throughout the year. Social attraction, particularly during daytime, was a key driver for interactions. Shoaling behavior substantially increased during daytime in the wintertime, whereas in summer carp interacted less frequently, but the interaction duration increased. Therefore, smaller, characteristic groups were more common in the summer months and during nighttime, where the social memory of carp lasted up to two weeks. Conclusions: We conclude that social relationships of carp change diurnally and seasonally. These patterns were likely driven by predator avoidance, seasonal shifts in lake temperature, visibility, forage availability and the presence of anoxic zones. The techniques we employed can be applied generally to high-resolution biotelemetry data to reveal social structures across other fish species at ecologically realistic scales.