單元大綱

  • Fishing nets pulled by a boat are called "boat seine." There are two types: "haul nets," in which the net is pulled by a stopped boat, and "trawl nets," in which the net is pulled over a long distance while the boat is moving forward. Among trawl nets, the one that uses an otter board (aperture board) to deploy the trawl net is called an otter trawl, and is a fishing tool and method widely used in Japan, the U.S., and Europe due to its excellent gathering efficiency. Otter trawls are also used as an effective sample collection method in fisheries resource surveys on fisheries research ships. This section describes the two types of otter trawls used on the Hokkaido University's Training Ship Oshoro-Maru, one for surface and the other for bottom trawling. Surface and bottom tows are used according to which part of the ocean (surface or bottom) is to be towed.


    • オッタートロール

      Figure 1 Otter trawl

      オッターボート: otterboat トロール網: trawl 先袖浮子: Tip Sleeve Floaters フロントウェイト: frontweight

      a) For bottom trawling: The resistance of the otter board spreads the net horizontally, allowing it to be towed over a wider area of the seafloor. 

      b) For surface and mid-water: By attaching floats or weights to the towline, the net opening can be widened vertically.

      The size of the otter board in relation to the trawl net is shown larger than actual size.