Annual reproductive cycle, age and body size at maturity, and potential and relative fecundity were examined in female willowy flounder in the North Pacific off Japan. Vitellogenesis became active from September, followed by the beginning of spawning in December. The spawning season continued until May with its peak in January. Estimated maturation rate was 50% at a standard length of 16 cm, 30% in 2-year-olds, and almost 100% in Ն3-year-old fish. Potential fecundity increased with age, while relative fecundity decreased in older fish. The results clarify some aspects of the detailed reproductive biology of female willowy flounder and emphasize the importance of age-composition data in estimating reproductive potential within a population.KEY WORDS: age and standard length at maturity, fecundity, reproductive cycle, willowy flounder.

Off Fukushima, Japanese flounder (Paralichthys olivaceus) is a highly-valued species supporting coastal and offshore fisheries. We developed an age-structured population model incorporating seasonal coastal-offshore migrations to estimate and predict the abundance of Japanese flounder off Fukushima, where fishing has been restricted since the 2011 Fukushima Dai-ichi Nuclear Power Plant (FNPP) accident. We estimated the abundance of Japanese flounder using catch per unit effort from coastal gill net and offshore bottom trawl fishing from January 2000 to February 2011 and predicted the abundance under two different fishing effort scenarios (the same effort level as 2010 or decreased effort after the FNPP accident). Estimated abundance reflected the seasonal coastal-offshore migrations well, and it was estimated that abundance increased during and after 2007 because of high recruitments. In contrast, it was concluded that the predicted abundance on and after 2012 increased owing to the decreased fishing effort because the same estimated recruits were used in both scenarios. This indicates that the waters off Fukushima have effectively been serving as a marine protected area for Japanese flounder since the FNPP accident. This result was validated because almost all (83%) of the observed abundance index values calculated from a scientific bottom trawl survey during 2003-2014 were included within the estimated (predicted) 95% credible intervals of estimated (predicted) abundance index in the period. We also demonstrated the model's applicability for estimating the optimal fishing effort and age at first landing to maximize the earnings from gillnet and bottom trawl fisheries.

Seasonal changes were analyzed in the distribution of the conger eel Conger myriaster in the waters south of Tohoku, Japan, from Sendai Bay to the Joban coast, using catch per unit effort data of trawl vessels, and the relationship was examined between distribution and water temperature at 100 m depth, in 1999 and 2000. Although the conger eel was distributed throughout the study area, it was rare north of 37 ∞ 40 ¢ N during February and March in both years. This scarcity corresponded to the occurrence of water colder than 10 ∞ C. Total length, age, gonad somatic index, and condition factor were not significantly different between eels caught north of 37 ∞ 30 ¢ N and those caught south of 36 ∞ N. Therefore, the seasonal change in conger eel distribution within the study area seems to be a seasonal loop migration driven by avoidance of cold water.KEY WORDS: Conger myriaster , CPUE, north-south migration, water temperature.

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The maturation rate and the spawning period of ‰athead ‰ounder Hippoglossoides dubius oŠ Fukushima Prefecture, which were caught from 2004 to 2006 (n＝7,341), were studied. The maturation rate of females was studied by the macroscopic observation of gonads and otolith aging. Estimated maturation rate was 50 at a total