Kom fyke monitoring

Since 1959 fish monitoring has been conducted with a fyke in the Marsdiep at the head of Texel. While the fyke is present, between March and October, it is checked upon every day. Caught fish are identified and measured at NIOZ. The fyke provides long-term monitoring data about seasonal and yearly abundances of fish stocks.

The passive fish trap of NIOZ is located near the entrance of the Dutch Wadden Sea. Photo: Marco Kortenhoeven.

Long-term monitoring

This so-called 'kom-fyke' has a leader of 200 m running from above the high water mark into the subtidal where two chambers collect the fish and other specimens. The stretched mesh-size of the leader and the chambers is 20 mm. In this area, the semidiurnal lunar tide is dominating and tidal range varies between 1 and 2 m depending on weather conditions and lunar phase. Tidal currents normally do not exceed 1 m/s, except for periods with strong wind stress.

Catches are sorted immediately, and all individuals were identified up to species level. For each species, numbers are counted and, when numbers are large, only wet mass is determined. If so, then wet masses were transformed into counts, using a fixed ratio per month, i.e. a fixed mean individual mass based on the actual measurements from 1970 onwards. All information is stored in a database and also available in Waddenzee Vismonitor.

In most years, the kom-fyke was removed just before winter because of potential damage by ice floes and in summer because of fouling of the net and potential clogging by macroalgae and jellyfish.