2026 Volume 90 Issue 1 Pages 35-43
The catch of the Japanese spiny lobster Panulirus japonicus in Ibaraki Prefecture has increased rapidly since the late 2010s, creating a need to collect data necessary for stock management. In this study, we investigated the carapace length (CL) and ovigerous stages in females based on market surveys conducted in 2023 and landing records from 2013 to 2023. For both sexes, 75% of the measured individuals had a CL of >63 mm, indicating that the spiny lobsters caught off the coast of northern Ibaraki Prefecture were larger and older than those caught in other major fishing areas in Japan. The estimated 50% maturity CL of females was 52.9 mm, and many individuals are caught after experiencing spawning for more than two years. In market surveys conducted in 2023, ovigerous females were observed between June and September. However, the analysis of landing records and water temperature data from 2013 to 2023 suggests that the timing of ovigerous female appearance varies greatly from year to year, with a recent rise in water temperature leading to their earlier and more prolonged appearance. Management strategies tailored to this marine area are necessary, given that spawning periods fluctuate.
