Distribution and size composition of the arctic lamprey Lethenteron camtschaticum in the North Pacific

Results of the long-term study of the spatial and vertical distribution of the parasitic anadromous Arctic lamprey Lethenteron camtschaticum (Tilesius, 1811) (Petromyzontidae) in the North Pacific and data on its size composition are given. This species is most frequent in the northwestern Sea of Japan and the western Bering Sea. The maximum concentrations are noted in waters of southern Primorye, southwestern Sakhalin, the northwestern part of the Sea of Okhotsk, and the northern part of the Bering Sea, which is probably explained by the increased number of its victims, Pacific salmon. Near the bottom, Pacific lampreys are extremely few and are primarily encountered at depths less that 400 m, and in the Pelagic zone, in the 100-m layer. The catches have contained Arctic lampreys having a total length of 15–79 cm. The lampreys of several size groups in the catches may indicate that L. camtschaticum spends not less than four years in the sea. No relationship has been found between the body length and the capture depth. Analyzed are the relationships between the body length and weight and the body length and the condition factor. The seasonal dynamics of these indices are considered.