INTEGRATION OF MICROPLASTIC MONITORING INTO RESOURCE SURVEYS OF COMMERCIAL FISH STOCKS: FIRST COMPARABLE DATA FROM THE NORTH PACIFIC SEAS (2020–2025)

Abstract

This paper presents generalized results of microplastic (MP) studies in the surface waters of the Far Eastern seas of Russia – the Sea of Okhotsk, the Bering Sea, and the northwestern Pacific Ocean area eastern of Kuril Island (NWPO) – based on data collected by VNIRO during expeditions conducted in 2020–2025. Sampling was performed using a Manta trawl (335 µm mesh) at 46 stations. Particle identification was carried out by Fourier-transform infrared spectroscopy (FTIR-ATR) with automated spectral matching against a reference library (match threshold >65 %). The MP contamination levels in the studied waters were lower compared to other regions of the World Ocean. The MPs pollution indices in the NWPO (Abundance Index, AI = 0.120 items/m³; frequency occurrence, FO = 100 %; range = 0.699 items/m³) significantly exceeded those recorded in the Bering Sea (AI = 0.028 items/m³; FO = 100 %; range = 0.049 items/m³) and the Sea of Okhotsk (AI = 0.020 items/m³; FO = 71.4 %; range = 0.338 items/m³). The distribution of MPs across all three study areas was characterized by spatial heterogeneity, with localized elevated concentrations (0.3–0.7 items/m³) associated with anticyclonic eddies and divergence zones. The 1.0–2.0 mm size fraction dominated the MP size composition across all areas (27.3 %); a high occurrence of particles <0.5 mm was recorded in the NWPO, while particles >5 mm were notably more frequent in the Sea of Okhotsk (9.9 %). Morphologically, fragments dominated in all seas (57.7–80.9 %), with an anomalously high occurrence of films observed in the Sea of Okhotsk (35.1 %), whereas primary MPs (pellets) were detected exclusively in the NWPO (3.7 %). The polymer composition was dominated by low-density polyethylene (including its oxidation products, identified as ionomers) and polypropylene, which collectively accounted for 82.0 % of all identified particles. The high proportion of oxidized polyethylene in the samples indicates prolonged residence times of plastic debris in the surface waters of the region. Differences among the study areas in terms of concentrations, size composition, morphology, and polymer composition were statistically significant (p < 0.001). The authors suggest that the spatial heterogeneity of MP pollution is driven by a combination of transoceanic particle transport by major currents, wind-driven surface drift during typhoon passages originating from southern oceanic regions, plastic release from melting ice, and the contribution of local sources in marginal seas.