[2020 AWARD WINNING PAPER] Comparison of biomass estimates from multiple stratification approaches in a swept area method for Pacific saury Cololabis saira in the western North Pacific

Fish Sci (2020) 86:pages445–456
DOI: https://doi.org/10.1007/s12562-020-01407-3

Authors

Midori Hashimoto, Hideaki Kidokoro, Satoshi Suyama, Taiki Fuji, Hiroomi Miyamoto, Miyako Naya, Dharmamony Vijai, Yasuhiro Ueno, Toshihide Kitakado

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.

Keywords

Swept area method / Fishery-independent survey / Pacific saury / Post-stratification / Sea surface trawl net / Stock assessment

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