Structure of settlements and resources of swifts scallop (Chlamys swiftii, Bivalvia) at the coast of Primorsky Region (Japan Sea)

Current state of Chlamys swiftii settlements and resources of this species in the coastal waters of Primorye (Japan Sea) are considered on the base of surveys conducted in 2007–2021. The data on spatial distribution and abundance of the scallops were obtained by methods of scuba counts at the depth < 20 m. The total biomass and abundance were calculated using the Voronoi diagrams (Thiessen polygons). In total, the data were analyzed for 13457 stations located along the entire coast of Primorye from the Tumannaya/Tumen River mouth to Cape Zolotoy where 2875 scallops were sampled, weighted and measured. The average density of Ch. Swiftii abundance and biomass distribution was estimated. The scallops do not form dense settlements suitable for commercial fishery. The settlements with the highest mean biomass (22.5 ± 5.0 g/m 2 ) were concentrated in the area from Cape Povorotny to Cape Yuzhny, and the lowest biomass of the settlements was observed in Peter the Great Bay (3.7 ± 2.1 g/m 2 ). The settlements had mosaic distribution. The total stock of the species is estimated as 1.4 . 10 3 t, the commercial stock – as 1.3 . 10 3 t. About 99 % of the total stock was concentrated at the eastern coast of Primorye in the area from Cape Povorotny to Cape Zolotoy. More regular and mass recruitment is noted for the settlements in this area, than in Peter the Great Bay. Percentage of scallops with non-commercial size varied from 1.9 to 19.0 %, by years, whereas the scallops at the age 3–7 years with shell height 70–110 mm dominated in the area from Cape Povorotny to Cape Zolotoy and those at the age 3–6 years with shell height 80–115 mm – in Peter the Great Bay. The modal age of Ch. Swiftii was 4 years, the oldest specimens reached 7–12 years, by surveys.