Biology subjects

Audzijonyte, A.

Publications and source records attributed to Audzijonyte, A..

9 recordsLinked to original sources

bioRxiv2025

Disregarding fish ageing method can compromise growth parameter comparability across studies

Reliable and comparable growth estimates are critical for accurate comparative studies, robust stock assessments, and effective fisheries management. Many studies compare fish growth Von Bertalanffy parameters (growth coefficient K and asymptotic length L{infty}) across species, populations, or time periods. These parameters are often obtained from literature or FishBase without accounting for ageing method used to estimate size-at-age, despite known differences in age estimates from different structures. In this study, we use four species as a case study and once again demonstrate that fish ageing based on otoliths and scales can produce significantly different estimates of L{infty} and K. We then analyse available K and L{infty} records from FishBase and show that L{infty} values derived from scales were, on average, 15% higher than those obtained from otoliths, while K values were 20% smaller (p < 0.01 in both cases). We strongly recommend that ageing methods be clearly reported in all growth studies and included in databases, that comparative analyses explicitly account for ageing method in statistical model structure, and that researchers consider methodological differences when interpreting growth parameter variations across studies.

ecology↗

bioRxiv2022

A machine learning based image classification method to estimate fish sizes from images without a specified reference object

Most fish populations around the world are unassessed and their status is unknown. Size based methods could provide fast and transparent assessments, but they require information on fish sizes. Citizen science programs, social media and smart phone applications generate millions of georeferenced fish images globally. Machine learning based fish species and size identification could help turn these images into valuable data for population status assessments. We present a machine learning, image classification based method to identify fish size classes from photos of anglers holding fish. To train the model we group images into ten 5-10 cm size classes, similar to classes used in underwater visual fish surveys. The model was trained using 2602 images from angler citizen science platforms MyCatch and FishSizeProject. Although the number of images was limited, the model achieved an overall accuracy of ~50%. Importantly, the misidentification of size classes was consistent across 20 separate model training rounds, each conducted with an independent, random allocation of images for training and test datasets. Our method suggests that photo based fish size class identification is feasible, and that prediction uncertainty should be incorporated into subsequent analysis, as it is done with fish ageing errors in fisheries stock assessments.

ecology↗

bioRxiv2022

Status and future perspectives for pikeperch (Sander lucioperca) stocks in Europe

Pikeperch (Sander lucioperca) is a European fresh and brackish water piscivorous fish, important as both a key predator and a valuable commercial and recreational fisheries species. There are concerns that some stocks are depleted due to overfishing and environmental changes. We review data collection and population assessments currently used for nine pikeperch stocks across six European countries and apply a unified assessment framework to evaluate population status and trends. For this we first standardised commercial, scientific, and recreational catch-per-unit-effort (CPUE) and catch time series and then applied Bayesian surplus production models. Our results showed that three stocks (including two in the Baltic Sea) were strongly depleted, with estimated biomasses considerably lower than the biomass at maximum sustainable yield (Bmsy). Other stocks were either close or higher than their estimated Bmsy. Looking at the trends, we find that four stocks (Lake Oulujarvi, Kvadofjarden, Lake Peipsi and Lipno) showed increasing biomass trends and two (Curonian Lagoon, Galtfjarden) had a strong decline in biomass. In most cases the stocks with clear signs of recovery were also those for which strong management strategies have been implemented. We find that, despite pikeperch being one of the most valuable inland fisheries, formalised stock assessments and regular surveys remain rare. Importantly, although most stocks are strongly targeted by recreational fishing, estimates of recreational catch are highly uncertain. We conclude that data limited stock assessment methods are useful for assessing fish population status and highlight an urgent need to improve pikeperch scientific monitoring and assessment of recreational catches.

ecology↗

bioRxiv2022

High-resolution app data reveal sustained increases in recreational fishing effort in Europe during and after COVID-19 lockdowns

It is manifest that COVID-19 lockdowns extensively impacted human interactions with natural ecosystems. One example is recreational fishing, an activity which involves nearly 1 in 10 people in developed countries. Fishing licence sales and direct observations at popular angling locations suggest that recreational fishing effort increased substantially during lockdowns. However, the extent and duration of this increase remain largely unknown due to a lack of objective data. We used four years (2018 to 2021) of anonymous, high-resolution data from a personal fish-finder device to explore the impact of COVID-19 lockdowns on recreational fishing effort in four European countries (Lithuania, the Czech Republic, Denmark, and Germany). We show that device use and, by extension, angling effort increased 1.2-3.8 fold during March-May 2020 and remained elevated even at the end of 2021 in all countries except Denmark. Fishing during the first lockdown also became more frequent during weekdays. Statistical models with the full set of fixed (weekdays, lockdown, population) and random (season, year, administrative unit) factors typically explained 50-70% of the variation, suggesting that device use and angling effort were relatively consistent and predictable through space and time. Our study demonstrates that recreational fishing behaviour can change substantially and rapidly in response to societal shifts, with profound ecological, human well-being and economic implications. We also show the potential of angler devices and smartphone applications to supply data for high-resolution fishing effort analysis and encourage more extensive science and industry collaborations to take advantage of this information. Significance statementRecreational fishing is a popular and widespread activity with ecological, social and economic impacts, though problematic to assess and manage due to a paucity of information regarding effort and catch. Here, we use high-resolution data from a personal angler sonar device to show how the COVID-19 pandemic changed angler behaviour and fishing effort across Europe. We demonstrate that angling effort doubled and remained higher at the end of 2021 than before the first lockdowns. Such rapid and profound changes could have significant consequences for aquatic ecosystems, possibly requiring new management approaches. We encourage the adoption of novel data from angler devices, citizen science, and more active science-industry collaborations to improve recreational fishing assessment and management.

ecology↗

bioRxiv2022

Does the Ice Age legacy end in Central Europe? The shrinking distributions of glacial relict crustaceans

O_LIGlacial relict mysid and amphipod crustaceans are characterised by their affinity for cold and well-oxygenated waters and inability to disperse upstream or by external agents. These crustaceans occur in large and deep lakes of Northern and Central Europe and North America, their distributions shaped by glaciation events. In Europe, along the southern edge of their distribution (Germany, Poland, Lithuania, Belarus), glacial relict crustaceans are threatened by eutrophication and global warming. C_LIO_LIThis study assesses the status of three glacial relict malacostracan species in Lithuania; the amphipods Monoporeia affinis and Pallaseopsis quadrispinosa, and mysid Mysis relicta, and models their abundance as a function of environmental variables and the presence of invasive Ponto-Caspian mysids and amphipods. C_LIO_LIOur results revealed that M. affinis is likely extinct in the country, whereas M. relicta was found in only 9 out of 16 locations from which it was previously recorded. The distribution of P. quadrispinosa appears to be shrinking. C_LIO_LILake depth and water flowthrough intensity were significantly and positively associated with the relative abundance of relict mysids and amphipods, but no association was found with lake size or the presence of invasive Ponto-Caspian crustaceans. C_LIO_LIWe conclude that urgent action to mitigate the effects of nutrient run-off is needed to improve the status of glacial relict and other species that require good water quality. We also propose the re-introduction of glacial relict species in Lake Dr[u]k[s]iai, where they went extinct during the operation of the Ignalina nuclear power plant that heated the lake, but where deep-water environmental conditions have improved following the powerplant closure in 2010. C_LI

ecology↗

bioRxiv2022

A scalable open-source framework for machine learning based image collection, annotation and classification: a case study for automatic fish species identification

Citizen science platforms, social media and multiple smart phone applications enable collection of large amounts of georeferenced images. This provides a huge opportunity in biodiversity and ecological research, but also creates challenges for efficient data handling and processing. Recreational and small-scale fisheries is one of the fields that could be revolutionised by efficient, widely accessible and machine learning based processing of georeferenced images. The majority of non-commercial inland and coastal fisheries are considered data poor and are rarely assessed, yet they provide multiple societal benefits and can have large ecological impacts. Given that large quantities of fish observations and images are being collected by fishers every day, artificial intelligence (AI) and computer vision applications offer a great opportunity to improve data collection, automate analyses and inform management. Yet, to date, many AI image analysis applications in fisheries are focused on the commercial sector and are not publicly available for community use. In this study we present an open-source modular framework for large scale image storage, handling, annotation and automatic classification, using cost- and labour-efficient methodologies. The tool is based on TensorFlow Lite Model Maker library and includes data augmentation and transfer learning techniques, applied to different convolutional neural network models. We demonstrate the implementation of this framework in an example case study for automatic fish species identification from images taken through a recreational fishing smartphone application. The framework presented here is highly customisable for further advancement and community based image collection and annotation.

ecology↗

bioRxiv2022

Changes in benthic and pelagic production interact with warming to drive responses to climate change in a temperate coastal ecosystem

Changing sea temperatures and primary productivity are rapidly altering marine ecosystems, but with considerable uncertainty in our understanding of the relative importance of these drivers and how their interactions may affect fisheries yield through complex food webs. Such outcomes are more difficult to predict for shallow coastal ecosystems than those in pelagic and shelf habitats, because coastal food webs are fuelled by a combination of separate pelagic and benthic energy pathways. Using long-term, empirical field data, we developed a novel multispecies size spectrum model for shallow coastal reefs. We include size-structured benthic and pelagic resources and trophic structures, allowing us to explore potential climate change scenarios that involve varying combinations of warming with changes in benthic and pelagic resources. Our model predicts that changes in resource levels will have much stronger impacts on fish biomass and yields than changes driven by physiological responses to temperature. Under increased plankton abundance, species in all trophic groups were predicted to increase in biomass, average size and yields. By contrast, changes in benthic resource produced variable responses across coastal trophic groups. Increased benthic resource led to increasing benthivorous and piscivorous fish biomass, yields and mean body sizes, but decreases in herbivores and planktivores. When resource changes were combined with warming seas, physiological responses generally decreased species biomass and yields. Our results suggest that the source, size and abundance of primary and secondary producers are critical to understanding impacts of warming seas on coastal fish communities. Understanding changes in benthic production and its implications for coastal fisheries requires urgent attention. Our modified size spectrum model provides a framework for further study of benthic and pelagic energy pathways that can be easily adapted to other ecosystems.

ecology↗

bioRxiv2022

Impacts of recreational angling on fish population recovery after a commercial fishing ban

It is often assumed that recreational fishing has negligible impact on fish stocks compared to commercial fishing. Yet, for inland water bodies in densely populated areas, this is unlikely to be true. In this study we demonstrate remarkably variable stock recovery rates among different fish species with similar life histories in a large productive inland freshwater ecosystem (Kaunas Reservoir, Lithuania), where all commercial fishing has been banned since 2013. We conducted over 900 surveys of recreational anglers during a period of four years (2016 to 2021) to assess recreational fishing catches. These surveys are combined with drone and fishfinder device-based assessment of recreational fishing effort. Fish population recovery rates were assessed using standardised catch per unit effort time series. We show that recreational fishing is having a major impact in retarding the recovery of predatory species, such as pikeperch and perch. In contrast, recovery of roach, rarely caught by anglers, has been remarkably rapid and the species is now dominating the ecosystem. Our study demonstrates that recreational fishing can have strong impacts on some fish species, alter relative species composition and potentially change ecosystem state and dynamics.

ecology↗

bioRxiv2021

Bottom-up and top-down effects of temperature on body growth, population size spectra and yield in a size-structured food web

Resolving the combined effect of climate warming and exploitation in a food web context is key for predicting future biomass production, size-structure, and potential yields of marine fishes. Previous studies based on mechanistic size-based food web models have found that bottom-up processes are important drivers of size-structure and fisheries yield in changing climates. However, we know less about the joint effects of bottom-up and physiological effects of temperature; how do temperature effects propagate from individual-level physiology through food webs and alter the size-structure of exploited species in a community? Here we assess how a species-resolved size-based food web is affected by warming through both these pathways, and by exploitation. We parameterize a dynamic size spectrum food web model inspired by the offshore Baltic Sea food web, and investigate how individual growth rates, size-structure, relative abundances of species and yields are affected by warming. The magnitude of warming is based on projections by the regional coupled model system RCA4-NEMO and the RCP 8.5 emission scenario, and we evaluate different scenarios of temperature dependence on fish physiology and resource productivity. When accounting for temperature-effects on physiology in addition to on basal productivity, projected size-at-age in 2050 increases on average for all fish species, mainly for young fish, compared to scenarios without warming. In contrast, size-at-age decreases when temperature affects resource dynamics only, and the decline is largest for young fish. Faster growth rates due to warming, however, do not always translate to larger yields, as lower resource carrying capacities with increasing temperature tend to result in declines in the abundance of larger fish and hence spawning stock biomass. These results suggest that to understand how global warming affects the size structure of fish communities, both direct metabolic effects and indirect effects of temperature via basal resources must be accounted for.

ecology↗