Trap net fishery

A Traditional Way of Fishing

In the Archipelago Sea, trapnet fishery represents the traditional way of catching herring. Although also new types of floating trapnets have been tested to some extent, most trapnets are anchored by ropes, weights and stakes on traditional nearshore locations, usually on or close to herring spawning beds. The intensity of trapnet fishery has decreased during last two decades, and the amount of trapnets has diminshed dramatically, as well as total trapnet catch. The catches per unit effort, however, have not been decreasing.

Herring trap net catch
Photo: Johannes Sahlsten

Trap Net Fishing

In the Archipelago Sea, spawning herring are mainly caught by trap nets, which are placed on the spawning beds or in their vicinity in spring. Trap net fishery largely follows the natural rhythm and behavior of spawning: the trap nets are set when herring is expected to start spawning, and the fisheries are continued as long as there is fish enough to make fishing economically profitable. Because the shores are different as to the bottom profile, quality, depth etc., the trap nets are usually made to measure for a specific location and are used in the same place over years. Traditionally, herring trap nets are fixed to the bottom with long wooden stakes, but also floating trap nets have been brought into use in some areas recently. The largest trap nets used in Airisto may hold 15-20 tons of herring at a time, but most nets are smaller.

In the herring trap nets in Airisto, the mesh size is 12-13 mm (knot-to-knot measure). There are no studies on the selectivity of the herring trap nets, but unlike gill-nets or trawls, commercial trap nets are considered as non-selective gear. They catch herring irrespective of size, age, sex and reproductive stage and even small herrings (ca 10 cm in length) are retained inside the trap.

In the early 1980’s, there were about thousand trap nets in the Archipelago Sea. The traditional method of fishing spawning herring has largely been abandoned since then and the trap net catch of herring has decreased as a consequence of this. However, the catch per unit effort (CPUE; tons/trap net) shows no decreasing trend but basically seems to be dependent on the size of the spawning stock in the Bothnian Sea (ICES subdivision 30, see map).

Related Publications

  • Rajasilta, M., Eklund, J., Kääriä, J. & Ranta-aho, K. 1989. The deposition and mortality of the eggs of the Baltic herring, Clupea harengus membras L., on different substrates in the south-west archipelago of Finland. – J. Fish. Biol. 34: 417-427.
  • Rajasilta, M., Eklund, J., Kääriä, J. & Ranta-aho, K. 1989. The deposition and mortality of the eggs of the Baltic herring, Clupea harengus membras L., on different substrates in the south-west archipelago of Finland. – J. Fish. Biol. 34: 417-427.
  • Rajasilta, M., Eklund, J. Hänninen, J., Kurkilahti, M., Kääriä, J. Rannikko, P. & Soikkeli, M. 1993. Spawning of herring (Clupea harengus membras L.) in the Archipelago Sea. – ICES J. mar. Sci. 50: 233-246.
  • Kääriä, J., Rajasilta, M., Kurkilahti, M. & Soikkeli, M. 1997. Spawning bed selection by the Baltic herring (Clupea harengus membras) in the Archipelago Sea of SW Finland. – ICES J. mar. Sci. 54: 917-923.
  • Griffin, F.J., Pillai, M. C., Vines, C. A., Kääriä, J., Hibbard-Robbins, T., Yanagimachi, R. & Cherr, G. N. 1998. Effects of salinity on sperm motility, fertilization, and development in the Pacific herring, Clupea pallasi. Biol. Bull. 194: 25-35.
  • Vahteri, P. & Vuorinen, I. 2001. The crash in Baltic herring (Clupea harengus membras L.) reproduction – a case study in the northern Airisto spawning grounds, Archipelago Sea S-W Finland. Baltic Sea Science Congress 2001, Abstract Volume. Stockholm University, Stockholm, Sweden.