Difference in number and size of ayu [Plecoglossus altivelis] larvae collected with a cone net towed at the bow side and stern
2004
Tago, Y. (Toyama-ken. Fisheries Experiment Station, Namekawa (Japan))
Abstract: Difference in number and size of ayu Plecoglossus altivelis larvae collected by bow side tow and stern tow of a ship was examined in the inner part of Toyama Bay in 1999. The tows were conducted eight times using two larvae nets at the same time. The mean lengths of larvae collected at the bow side ranged from 4.9 =+- : 0.3 to 10.9 :=+-: 6.2 SD mm, whereas those collected at the stern ranged from 5.2 to 7.6 :=+-: 1.6 mm. The lengths of larvae collected at the bow side were distributed significantly to a larger size compared with those collected at the stern. In water tank experiments ayu larvae escaped from the surface to the bottom when an object was thrown and floated on the surface. These facts suggest that in collecting ayu larvae at the rear of a ship, larger larvae tend to escape from the surface in fright response of approaching ship. Some of larvae collected at the middle layer by a larvae net towed at the rear of the ship might, in fact, inhabit the surface layer. It is concluded that bow side tow is more effective than stern tow in collecting ayu larvae inhabiting the surface layer.
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