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MorphoCal: a multi-stage deep learning framework for fish length estimation in challenging underwater pond environments

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Introducing MorphoCal, a groundbreaking multi-stage deep learning framework designed for precise fish length estimation in challenging underwater pond environments. Accurate assessment of fish pose and body length is vital for understanding aquatic behavior and biomass dynamics, yet factors like turbidity and uneven lighting complicate traditional methods. This study presents MorphoCal, integrating AquaYOLO-PoseCA for enhanced keypoint detection and a calibration module for centimeter-level accuracy. The resulting framework supports effective noninvasive monitoring, crucial for intelligent aquaculture systems.
MorphoCal: a multi-stage deep learning framework for fish length estimation in challenging underwater pond environments

The introduction of MorphoCal, a multi-stage deep learning framework for fish length estimation, marks a significant advancement in the field of underwater imaging and aquatic ecosystem monitoring. Accurate estimations of fish pose and body length are critical for understanding fish behavior, growth patterns, and biomass dynamics, which are essential components of sustainable aquaculture practices. As challenges such as turbidity, uneven lighting, and occlusion complicate underwater imagery, the development of robust technologies like MorphoCal becomes increasingly important. This innovation not only supports non-invasive monitoring but also holds promise for enhancing intelligent aquaculture systems, contributing to a more sustainable approach to fish farming and ecosystem management. The implications of such technological advancements are profound, especially in light of growing global pressures on marine resources.

Recent geopolitical events, such as the U.S. Conducts Self-Defence Strikes On Iranian Boats And Missile Sites Near Strait Of Hormuz and Iran's claims of downing a hostile drone over the Persian Gulf, underscore the complexities of managing marine environments. The need for accurate monitoring of marine life and habitats is becoming increasingly urgent as tensions rise and the potential for ecological disruption grows. Furthermore, the introduction of innovative technologies in maritime operations, such as Hyperion Systems' unveiling of the Southern Hemisphere’s First 3D-Printed Uncrewed Surface Vessel, highlights a shift towards integrating advanced technologies in marine management and research. These developments collectively point to a future where data-driven decision-making can help mitigate conflicts and promote sustainable practices.

MorphoCal's integration of AquaYOLO-PoseCA with a unique keypoint detection network demonstrates an innovative approach to capturing crucial data in challenging underwater conditions. The framework's ability to perform joint fish detection and keypoint estimation in a single-stage forward pass not only enhances computational efficiency but also improves the accuracy of fish length reconstructions, with deviations from ground truth measurements remaining minimal. This precision is vital for fisheries management and ecological studies, where accurate data can influence policies and conservation strategies. The success of MorphoCal in the DePondFi’24 dataset is a testament to the potential of machine learning applications in real-world conditions, bridging the gap between technology and ecological stewardship.

As we look forward, the broader significance of MorphoCal extends beyond its immediate applications. The framework's success paves the way for further research into automated monitoring systems that can adapt to various aquatic environments. With climate change and human activities increasingly impacting marine ecosystems, leveraging advanced technologies like MorphoCal will be essential for fostering sustainable practices. The question worth considering is: how can we further harness the power of machine learning and artificial intelligence to not only monitor but also proactively manage and protect our oceans? As the urgency for ocean stewardship grows, the integration of such technologies will be crucial in shaping the future of marine conservation efforts and ensuring the health of our aquatic ecosystems.

IntroductionUnderwater imaging plays an important role in monitoring aquatic ecosystems and aquaculture environments. Accurate estimation of fish pose and body length from underwater imagery is essential for analysing fish behaviour, growth patterns, and biomass dynamics. However, underwater scenes are often affected by turbidity, uneven illumination, occlusion, and suspended particles, which reduce the accuracy of keypoint detection and metric measurements.MethodsTo address these challenges, this study proposes MorphoCal, a multi-stage deep learning framework for fish pose estimation and geometric length reconstruction under real-world pond conditions. The framework integrates AquaYOLO-PoseC A, a coordinateattention–enhanced YOLO-based keypoint detection network, with a single-shot checkerboard calibration and ray–plane projection module for centimetre-level metric reconstruction. Coordinate Attention is incorporated into the YOLO backbone to encode direction-aware spatial features and preserve positional information, improving anatomical keypoint localization for elongated fish structures. The architecture performs joint fish detection and keypoint estimation in a single-stage forward pass using PAN–FPN feature fusion.ResultsExperiments on the DePondFi’24 dataset, consisting of multi-species fish captured under natural pond conditions, show that AquaYOLO-PoseCA achieves a bounding box mAP of 0.959, pose mAP of 0.848, and mAP50− 95 of 0.712, while maintaining computational efficiency with 29.4 GFLOPs and 11.4M parameters. The reconstructed fish lengths show low deviation from ruler-based ground truth measurements.DiscussionThe proposed MorphoCal framework enables reliable fish pose estimation and centimetre-level length reconstruction under challenging underwater conditions, supporting noninvasive fish monitoring, growth assessment, and biomass estimation in intelligent aquaculture systems.

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#autonomous underwater vehicles#climate monitoring#in-situ monitoring#MorphoCal#deep learning framework#fish length estimation#underwater imaging#aquatic ecosystems#AquaYOLO-PoseCA#keypoint detection#metric reconstruction#Coordinate Attention#PAN-FPN feature fusion#multi-species fish#bounding box mAP#pose mAP#centimetre-level#noninvasive fish monitoring#growth assessment#biomass estimation