Comparison of biomass estimates from multiple stratification approaches in a swept area method for Pacific saury Cololabis saira in the western North Pacific |
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Authors: | Hashimoto Midori Kidokoro Hideaki Suyama Satoshi Fuji Taiki Miyamoto Hiroomi Naya Miyako Vijai Dharmamony Ueno Yasuhiro Kitakado Toshihide |
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Institution: | 1.National Research Institute of Far Seas Fisheries, Japan Fisheries Research and Education Agency, 2-12-4 Fukuura, Kanazawa, Yokohama, Kanagawa, 236-8648, Japan ;2.Tohoku National Fisheries Research Institute, Japan Fisheries Research and Education Agency, 3-27-5, Shinhama, Shiogama, Miyagi, 985-0001, Japan ;3.Hachinohe Station, Tohoku National Fisheries Research Institute, Japan Fisheries Research and Education Agency, 25-259, Shimomekurakubo, Same, Hachinohe, Aomori, 031-0841, Japan ;4.National Centre for Biological Science, Tata Institute of Fundamental Research, Bellary Road, Bangalore, Karnataka, 560065, India ;5.National Research Institute of Fisheries Science, Japan Fisheries Research and Education Agency, 2-12-4 Fukuura, Kanazawa, Yokohama, Kanagawa, 236-8648, Japan ;6.Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo, 108-8477, Japan ; |
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Abstract: | Fishery-independent surveys using sea surface trawl nets for Pacific saury Cololabis saira in the western North Pacific since 2003 have enabled the investigation of their annual distribution patterns and total biomass during June and July, prior to the main fishing season in Japan. We compared biomass estimates and their associated variances derived based on five different post-stratification approaches in a swept area method, and then observed that these approaches have little effect on biomass estimates and their precision, owing to well-organized survey designs and homogeneously allocated sampling stations. We were able to utilize decreasing biomass estimates for 15 years as an essential abundance index in the ongoing stock assessment. Notably, examination based on stratification along with longitudinal survey lines indicated that the estimated biomass had decreased in the western survey area, resulting in an eastward shift in the gravity center of Pacific saury distribution after 2010. We recommend biomass estimation in an east–west direction based on longitudinal stratification as an effective measure to develop population dynamics models which reflect westward migration into the fishing grounds around Japanese coastal waters, and to forecast the expected catch during the subsequent fishing period. |
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