Northernmost record of the giant tiger prawn Penaeus monodon from estuaries in Ibaraki Prefecture, eastern Japan

The black tiger shrimp Penaeus monodon, a commercially important species in Southeast Asian countries, has been recorded from tropical to temperate regions of the Indo-West Pacific. The northernmost record of the species has been from Tokyo Bay or the Boso Peninsula, central Japan. In this study, we report the occurrence of P. monodon based on 20 juvenile specimens (4.8–28.3 mm in carapace length) collected from the Edokami, Kuji, Naka and Tone River estuaries, and the brackish water Lake Hinuma (35°48'N to 36°49'N, 140°32'E to 140°47'E), all located in Ibaraki Prefecture north of Tokyo Bay and the Boso Peninsula, from September 2021 to November 2023, showing the northward expansion of distributional range of the species. Periods of high water temperature (> 20 ºC) partly associated with warm water intrusion from the Kuroshio from 2021 to 2023 persisted twice as long as the previous 30-year average for the region. Recruitment of P. monodon juveniles to the above estuaries may increase in the near future due to rising water temperatures, although a lack of tolerance to low water temperatures as shown in previous studies suggests that overwintering in coastal waters of Ibaraki Prefecture should be unsuccessful.