Estimation of standing stock and factors affecting the stock fluctuation of asari clam Ruditapes philippinarum in four regions of Ise Bay, Japan

Abstract

In order to determine the factors affecting the stock fluctuation of asari clam Ruditapes philippinarum in Ise Bay, Japan, we examined the high-density depth zones (i.e., centers of distribution) of R. philippinarum and standing stocks at three depth zones (depth zone I: shallower than water depth 1 m; depth zone II: water depth 1–5 m; depth zone III: water depth 5–10 m) in the four regions (the Suzuka region including the Wakamatsu and Shiroko subregions, the Karasu region, the Matsusaka region including the Miwatarigawa and Matsunase subregions, and the Ise region) of Ise Bay, Japan, from 2012 to 2014. Based on the comparison of clam densities among depth zones in each region, the depth zones I were the centers of distribution in the Karasu, Matsusaka, and Ise regions from 2012 to 2014, while the depth zone II was considered as the center of distribution in the Shiroko subregion of the Suzuka region in November 2013 and May 2014. In May 2014, the standing stock of asari clam in the Suzuka region was 4,246 metric tons, which was the largest among the four regions from 2012 to 2014. The standing stock at depth zone III with a large area accounted for 70% of the stock in the Suzuka region in May 2014. A relationship between the standing stock and dissolved oxygen concentration (DO) suggested that the appearance/disappearance of hypoxia water masses (DO≤3 mg・L^-1) affected large fluctuation in standing stocks.