Pike wetland – Do they have any importance for the Baltic Sea coastal area?

Pike is one of Sweden’s most common predatory fish. As a predator at the top of the food chain, it also plays an important role in the way the ecosystem functions. Unfortunately, pike stocks in the Baltic Sea have fallen sharply in recent decades. One way of strengthening stocks is to construct so-called pike wetlands (wetlands suitable for use by predatory fish for the purposes of reproduction), but is this having any noticeable effect? Supported by BalticSea2020, this project will investigate whether pike wetlands are increasing stocks along the Baltic Sea coast.

“Pike wetlands” is a restoration or renovation of wetland areas optimal for reproduction by predatory fish. Studies have shown an extraordinary increase in pike fry – for example, at the Kronobäck pike plant at Kalmarsund, the increase has been from 3,000 to 300,000 fry within a few years of the measure having been taken*. Construction of pike wetlands has therefore been proposed as a central measure for recreating the Baltic Sea coastal ecosystem and improving the opportunities for sport fishing, recreation and tourism. For example, in 2010 Sportfiskarna (the Swedish Anglers Association), with the support of BalticSea2020, began a project where a large number of pike wetlands have been restored and created offering excellent spawning opportunities (link). The project was completed in 2012 and has identified wetlands appropriate for restoration as pike spawning grounds along the Swedish east coast up to Gävle.

This project will investigate whether productive pike wetlands contribute to there being more adult pike (i.e. increased pike stocks) along the Baltic Sea coast together with positive effects on ecosystems and community activitiessuch as sport fishing, fishing tourism and a living coastal environment.

The project will compare coastal bays with a pike wetland (PW) to bays where no action has been taken (reference area, REF). Four appropriate coastal areas have been identified where valuable background data, such as the number of migratory adult fish and emigrant fry around the pike wetlands may be found:

  • Timmernabbenviken (PW) vs. Tokö (REF),
  • Lervik (PW) vs Ödängla South (REF),
  • Harfjärden (PW) vs Sjövik/Hästhagen (REF),
  • Kalmar Dämme South (PW) vs Knarrö West (REF).

Over a two-year period (autumn 2017 - autumn 2019), the project will: 1) quantify and compare the pike populations of coastal areas adjoining the pike wetlands and in reference areas where no measures have been taken (using test angling); 2) quantify the relative “export” of pike from the pike wetland to the coastal area (to obtain a more detailed understanding of the effects of the pike wetland on pike stocks along the coast); 3) genetic studies to highlight population dynamics (i.e. obtain answers to which, in what proportion and where the various pike wetlands contribute to stocks along the coast); and 4) Otolytic studies** to investigate whether the proportion of freshwater spawning pike has changed compared with previous studies.

The results and conclusions of the project will ultimately be described in a report illustrating the impact of pike plants on pike stocks. The report will be made available to the relevant authorities, municipalities, other stakeholders and the public in general.

* Nilsson et al. (2014), Larsson at al. (2015).
** Traditional age-assessment of fish carried out by examining their statoconia, so-called, otoliths. The otolith grows at the same rate as the fish, forming annular rings which may be counted in a similar way to annual growth rings on a tree.



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Project status

Start: 2017-09-01
End: 2020-03-31

Project manager

Per Larsson, Professor Linnaeus University, Kalmar

Contact at BalticSea2020