Gill net selectivity and the effectiveness of resource management for Pacific herring (Clupea pallasii) in Ishikari Bay
2017
Hoshino, N. (Central Fisheries Research Institute, Hokkaido Research Organization, Yoichi, Hokkaido (Japan))
Experimental gill net fishing was performed at the end of the fishing seasons in 2015-2017 to ascertain the characteristics of Pacific herring (Clupea pallasii) stocks in the coastal waters of Ishikari Bay. Samples collected using gill nets with different mesh sizes were mostly composed of 2- and 3-year-old mature fish. Gill net selectivity was estimated based on direct estimation and the SELECT method. Using Akaike information criterion, a log-normal model was selected as the best-fitted selectivity curve. The modes of the selectivity curves were estimated to be 243, 269, 296, and 323 mm fork lengths for the popular mesh sizes, 55, 61, 67, and 73 mm, respectively. Catching efficiencies of gill nets with a 61 mm mesh size, which is the lower limit for mesh size as per recent fishing regulations, were estimated to be 5% and 65% for the 2- and 3-year-old fish, respectively. These results suggest that the recent fishing regulations have considerably enhanced the spawning biomass of Pacific herring.
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