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Endo T.,Ibaraki University | Kanou K.,Ibaraki University | Tokoro F.,Ibaraki Fisheries Research Institute | Arai M.,Ibaraki Fisheries Research Institute | Katayama S.,Tohoku University
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2017

Age and growth rates of the invasive exotic catfish Ictalurus punctatus were assessed by examination of otolith sections of 937 specimens (3.8-57.2 cm in standard length, SL) collected in Lake Kitaura, Ibaraki Prefecture, Japan. An opaque zone on the otolith margin, formed once a year from May to June, coincided with the peak spawning season. Von Bertalanffy growth equations differed significantly between sexes, being SLt = 63.5{1? exp[?0.120(t +0.416)]} for males and SLt= 56.5{1-exp[-0.134(t +0.437)]} for females [SLt is SL (cm) att (year)]. The estimated maximum ages for males and females were 14 and 13 years, respectively. An age-length key for converting length frequencies into age frequencies was established, and is a useful tool for assessing the population status of the species and the development of effective management strategies. © 2017 The Japanese Society of Fisheries Science.

Sakamoto D.,Tokyo University of Marine Science and Technology | Nemoto T.,Ibaraki Fisheries Research Institute | Sunoh N.,Ibaraki Fisheries Research Institute | Iwasaki J.,Ibaraki Fisheries Research Institute | And 6 more authors.
Fisheries Science | Year: 2014

We estimated the population size of the pond smelt Hypomesus nipponensis at the beginning of the fishing season in Lake Kasumigaura and Lake Kitaura, Japan using two DeLury methods and cohort analysis. A growth curve was estimated on the basis of monthly standard length. The relationship between standard length and weight was utilized for calculating the mean weight on the survey day in a particular month. Total monthly catches in Lake Kasumigaura and Lake Kitaura were calculated using partial monthly pond smelt catch obtained from processing plants located near the lakes between July and December. The total monthly catch was calculated from the total monthly catch weight and the monthly mean weight. The number of boats operating each month, compiled by the Kasumigaura-Kitaura Fisheries Office of Ibaraki Prefecture, was also employed. The estimated initial population sizes were compared with the population level index (PLI) estimated from survey data before the start of the fishing season. No significant differences were detected among the initial population sizes estimated by DeLury method, cohort analysis and PLI. The estimates ranged from 7.4 million to 410 million in Lake Kasumigaura, and from 7.7 million to 44 million in Lake Kitaura. © Japanese Society of Fisheries Science 2014.

Arayama K.,Ibaraki Fisheries Research Institute | Sunoh N.,Ibaraki Fisheries Research Institute | Yamazaki Y.,Ibaraki Fisheries Research Institute | Yamazaki Y.,Ibaraki Prefectural Fisheries Research Institute
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2014

We studied the distribution patterns of ayu Plecoglossus altivelis larvae and juveniles in the coastal waters adjacent to the Kuji River estuary to identify their nursery areas. Fish were collected using a purse seine (mesh size of the cod end: 2 mm) in the survey area, which had a depth of about 3 to 18 m. Ayu (13.6-87.7 mm in standard length) were caught mainly between November and April from areas with a depth of less than 10-12 m near the coastline, such as sandy beaches and the Kuji River mouth. The first occurrence of the larvae was found at the offshore zone beyond the breaker zone of sandy beaches. The ayu extended their distribution from shallow to deep waters as they developed, and individuals that were born earlier tended to extend their distribution first. The nursery areas of ayu expanded to areas shallower than approximately 10 m, near the coastline and river mouth. Moreover, the offshore zone beyond the breaker zone of sandy beaches was important for larvae recruited to the nursery areas.

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