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Watanabe Y.,University of Tokyo | Suzuki T.,University of Tokyo | Tsuno K.,Kochi Prefectural Fisheries Experimental Station
Fisheries Science

Seasonal variation in daily growth rates in the early and middle larval stages of round herring Etrumeus teres were largely determined by the sea temperatures experienced by hatch-date cohorts in the Pacific coastal waters off southern Japan. Round herring larvae were collected by purse seining in the coastal waters of central Tosa Bay. A total of 451 larvae were aged by reading daily rings in otoliths. Individuals within a range of 2-5 hatch dates were grouped as hatch-date cohorts. We selected 16 cohorts that hatched during September 2000 and March 2002 and calculated mean widths of otolith growth increments for each cohort during the first feeding stage (W FF, increments 1-5) and the maximum increment width in the middle larval stage (W MAX). Seasonal variation in mean W FF and W MAX among the 16 cohorts was largely (80-90 %) explained by the sea temperature in the bay. These results indicate that temperature was a predominant determinant of larval growth rates; other environmental factors, such as food availability, did not substantially affect growth rates of round herring larvae in coastal waters along the subtropical Kuroshio Current off southern Japan. © 2013 The Japanese Society of Fisheries Science. Source

Kawamata S.,Japan National Research Institute of Fisheries Engineering | Taino S.,Kochi Prefectural Fisheries Experimental Station | Miyaji M.,Kochi University | Nakamura Y.,Kochi University
Nippon Suisan Gakkaishi (Japanese Edition)

Size-selective predation by Japanese spiny lobster Panulirus japonicus on the sea urchin Echinometra sp. A was examined in outdoor tanks with a roof using 20 lobsters (carapace length, CL: 59-93 mm) and four size classes (10-19, 20-29, 30-39 and 40-49 mm in test diameter, TD) of sea urchins. High levels of predation were found to occur in the period, at least until 5 days before and again from 3 days after molting. The maximum TD of eaten sea urchins increased with CL. The success rate of predation (ratio of the number of prey eaten to the number of predation attacks) was high (~75%) for the smallest size class of urchins but low (<11%) for the largest class over the experimental range of CL, and the success rate increased with CL for the intermediate classes, suggesting that large (>40 mm) sea urchins may be less vulnerable to predation even by large (>90 mm) lobsters. Prey remains after lobster predation showed that the tests of large (mostly >30-40 mm TD) sea urchins tended to remain largely intact with an enlarged peristomial opening while entire tests were eaten for smaller urchins. © 2016 The Japanese Society of Fisheries Science. Source

Noguchi S.,Nihon University | Itoi S.,Nihon University | Takai N.,Nihon University | Noda T.,Fisheries Research Agency | And 3 more authors.
Mitochondrial DNA

The gnomefish (Scombrops boops) is a member of the percoid family Scombropidae, which includes a single genus and three to four species worldwide. Since little is known about the ecology of this species, here, sequencing analysis of the cytochrome b gene (1141 bp) in mitochondrial DNA detected 101 haplotypes from 186 individuals of S. boops collected from waters at seven localities around the Japanese archipelago. A single haplotype (Sb2) was the most abundant in the combined populations of S. boops from various localities. Genetic population structure analyses revealed no significant differences among these populations (Fst = -0.0313-0.0195; Φst - 0.0505-0.0615) with high haplotype diversity and low nucleotide diversity. This suggests that S. boops around the Japanese archipelago constitutes a single population, and indicates that the genetic structure of this population may be influenced by larval and egg dispersal in association with warm currents. Source

Morita T.,Fisheries Research Agency | Niwa K.,Fisheries Research Agency | Fujimoto K.,Fisheries Research Agency | Kasai H.,Fisheries Research Agency | And 15 more authors.
Science of the Total Environment

Iodine-131 (physical half-life: 8.04days) was detected in brown algae collected off the Japanese coast. Brown algae have been extensively used as bioindicators for radioiodine because of their ability to accumulate radionuclides in high concentration factors. The maximum measured specific activity of 131I in brown algae was 0.37±0.010Bq/kg-wet. Cesium-137 was also detected in all brown algal samples used in this study. There was no correlation between specific activities of 131I and 137Cs in these seaweeds. The specific activity of 137Cs ranged from 0.0034±0.00075 to 0.090±0.014Bq/kg-wet. Low specific activity and minimal variability of 137Cs in brown algae indicated that past nuclear weapon tests were the source of 137Cs. Although nuclear power stations and nuclear fuel reprocessing plants are known to be pollution sources of 131I, there was no relationship between the sites where 131I was detected and the locations of nuclear power facilities. Most of the sites where 131I was detected were near big cities with large populations. Iodine-131 is frequently used in diagnostic and therapeutic nuclear medicine. On the basis of the results, we suggest that the likely pollution source of 131I, detected in brown seaweeds, is not nuclear power facilities, but nuclear medicine procedures. © 2010 Elsevier B.V. Source

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