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Sugawara M.,Hokkaido National Fisheries Research Institute | Yamashita N.,Hokkaido National Fisheries Research Institute | Sakaguchi K.,Hokkaido Research Organization HRO | Sato T.,Kushiro Fisheries Research Institute | And 5 more authors.
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2013

To identify factors affecting the somatic growth of the winter-spawning stock of Japanese common squid, the somatic growth of squid caught in the East China Sea, the Pacific Ocean and the Tsushima Strait from 2000 to 2011 was estimated using age determination from statolith microstructure analysis. The relationship between estimated age in days and dorsal mantle length was fitted using a Gompertz growth equation. The residuals of dorsal mantle length from the growth equation differed among year classes, hatch months, and sexes. Although no environmental factors correlated with the annual difference in growth, increased sea water temperature in spring in the Kuroshio-Oyashio transition region corresponded to increased growth with hatch month. Growth was smaller in males than in females during the southward migration, which suggested depressed growth in males due to earlier sexual maturation than in females.

Yazaki T.,Japan National Agriculture and Food Research Organization | Hirota T.,Japan National Agriculture and Food Research Organization | Iwata Y.,Japan National Agriculture and Food Research Organization | Inoue S.,Japan National Agriculture and Food Research Organization | And 8 more authors.
Agricultural and Forest Meteorology | Year: 2013

In the Tokachi region of Japan, soil frost depth has been decreasing. Outbreaks of volunteer potatoes caused by overwinter survival of unharvested potato tubers have become a severe nuisance. Some farmers have started snow plowing (. yukiwari in Japanese) to deepen soil frost and thereby freeze tubers to death. However, the system relies on farmer's intuition and experience and sometimes they fail to completely kill tubers. To establish a reliable volunteer potato control, we implemented farm testing of the vertical distribution of unharvested tubers and effects of soil frost control on the survival ratio. The control of volunteer potato by attaining adequate soil frost depth using snow plowing and accumulation termed as soil frost control. Furthermore, we compared tuber survival by soil frost control based on estimated soil frost depth by numerical soil temperature model and soil frost control based on farmers' voluntary effort. Most unharvested tubers are distributed at 0-0.15. m depths. The target soil frost depth was set as 0.30. m based on the relation between soil frost depth and tuber killing depth: the depth at which the soil temperature decreases to the critical temperature of -3. °C from a previous study. Soil frost control remarkably decreased survival to less than 0.5% of number of unharvested tubers if soil frost depth exceeded 0.30. m. Consequently, the target soil frost depth was confirmed as appropriate for almost complete tuber elimination. Soil frost control based on the estimated soil frost depth enhanced soil frost penetration more deeply and killed more tubers than soil frost control done by farmers' voluntary effort, thereby suggesting advantages of decision-making based on the estimated soil frost depth. Soil frost control is attracting attention and as a reliable method that can greatly reduce the outbreak of volunteer potatoes. The strategy minimizes climate change related risk. © 2013 Elsevier B.V.

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