In this study, a longline aquaculture facility with lantern nets off the coast of northern China was modelled to conduct hydrodynamic tests starting from the culture unit to the entire facility under various current and wave conditions. The experimental results indicated that the drag coefficients of the lantern net model with weights of 0.5, 0.75, and 1.0 kg were 0.75, 0.83, and 0.91, respectively, in the Reynolds number range of 1 × 10⁴–1 × 10⁶. The current-driven upstream mooring line was more dominant than the wave-driven tension, and a simplified model of the longline facility accurately predicted the mooring line tension under the current conditions. The scope of the mooring line (defined as the length of the mooring line related to the water depth) played an important role in eliminating an order of magnitude difference in mooring tension under the wave conditions. The amplitudes of the vertical movement of the longline facility were smaller than the wave height when L/L_m was less than 1.5. Therefore, detailed information is needed to better understand the hydrodynamic characteristics and motion response of longline aquaculture facilities for the safe operation of longline structures in offshore environments, in order to process high-quality oyster products.

Accurate assessment of microplastic pollution is hampered by the lack of standardized sampling protocols, particularly regarding microplastics lost in sampling. This study investigates the filtering mechanisms of microplastics during surface towing sampling (i.e., mesh-filtered methods) and develops a framework to correct abundance data. Paired-gear experiments using neuston nets (mesh sizes of 50-500 μm) were conducted in Xiangshan Bay, China. Microplastic retention and mesh selectivity were analyzed using SELECT models, and master selection curves were derived for fibrous and non-fibrous microplastics. Results show that larger mesh sizes (150, 330, 500 μm) significantly underestimate microplastic abundance by 1.4 to 2.9 times compared to a 50-μm net, with fibers being the primary contributor to losses. The filtration mechanisms differ fundamentally between shapes. For non-fibrous microplastics, retention is governed by physical interactions between the mesh opening and the particle’s shortest diameter. In contrast, the passage of fibrous microplastics is not determined by a simple size-exclusion rule. Their high flexibility allows bending and passage even at lengths far exceeding the mesh size. A mechanically stable, multi-span configuration forms when fiber length exceeds approximately 15 times the mesh size, making retention largely independent of further length increase. Based on the master selection curve, a harmonized assessment framework was established to re-evaluate data from 27 previous studies. The resulting mesh-specific correction factors highlight the severe underestimation of fibers by commonly used nets (e.g., 330 μm). This study clarifies shape-dependent filtration mechanisms in mesh-filtered sampling and provides a practical tool to enhance the comparability of historical and future microplastic monitoring data, advocating for standardized use of smaller mesh sizes for accurate fiber assessment.