In situ fish target strengths derived with a split-beam echo sounder

In-situ target strengths of six fishes were determined with a split-beam echo sounder during cruises about Lofoten in March 1984 and the Shetland Islands in July 1984. The species and lengths, mean and standard deviation, are the following: cod (Gadus morhua), 82 +- 11 cm, saithe (Pollachius virens), 57 +- 6 cm; Norway pout (Trisopterus esmarki), 18+- 2 and 15 +- 1 cm; herring (Clupea harengus), 28 +- 2 cm; redfish or ocean perch (Sebastes marinus), 20 +- 9 cm; and greater silver smelt (Argentina silus), 37 +- 4 cm. Extraction of unbiased mean target strenqths by a method of threshold compensation is described