Pike Numbers are Increasing in the Stockholm Archipelago – According to New Test Fishing

For several years, there have been warnings that pike stocks are declining in the Stockholm archipelago. Now, according to new test fishing, there is a clear reversal of the trend. Pike may be making a comeback.

^{Text: Arvid Wiclander Mellgren}

Henrik C. Andersson is a fisheries consultant at the Stockholm County Administrative Board and leads the ReFisk project—an initiative to strengthen predatory fish stocks in archipelago bays.

In 2019 and 2020, ReFisk conducted test fishing for pike in the bays of the Stockholm archipelago. At that time, pike stocks were found to be low, but when the test fishing was followed up this year, the results were much better.

“I’m a little surprised myself, there were insane amounts of fish in some bays,” says Henrik C. Andersson.

The test fishing was carried out using a new method – fishing rods. ReFisk’s method description states that “Each fisherman shall fish to the best of their ability throughout the experiment.”

Spin fishing – a risk of margin of error?

“Yes, it does, but that’s true of all test fishing methods. Even with nets and fyke nets. For pike in particular, fishing with a rod is more effective, as it is an ambush predator that mostly stays still”, says Henrik C. Andersson.

During this spring, they conducted test fishing in 26 bays, 13 of which are protected, meaning that fishing is otherwise prohibited. The other 13 were so-called reference bays for each of the protected bays in order to be able to distinguish the effect of protection in the results.

In one of the reference bays, Myttingeviken south of Ljusterö, far less than 0.5 pike per fishing rod per hour were caught in 2019 and 2020.

“Guarantees a certain increase in stock”

When the test fishing was followed up this spring, the change was clear. In Stockholm’s inner archipelago, this year’s test fishing showed a manifold increase in the number of catches.

In Myttingeviken, four pike were now caught per hour of fishing.

“The increases we are now seeing guarantee a certain increase in the stock, the difference is that big,” says Henrik C. Andersson.

Myttingeviken is the only reference bay with a higher catch frequency than its corresponding protected bay. Henrik C. Andersson believes that this indicates that protection is a management method that works and should be applied to more and larger areas. But even in the reference bays, catches were significantly higher than in 2019 and 2020.

“There has been a greater increase in protected areas, but there has been an increase in all bays in the inner archipelago. The change is not just an effect of protection. Something positive has happened,” says the fisheries consultant.

The key: Perch

Henrik C. Anderson does not know for certain why the pike population has recovered so strongly, but he believes that perch play an important role.

When there are too many sticklebacks in the archipelago bays, they eat many of the pike’s eggs. Pike generally do not eat much stickleback. But perch do.

“I believe that perch have the ability to correct the problems caused by stickleback. They are dedicated stickleback eaters,” he says.

Another person who believes that perch may have had a positive impact is Ulf Bergström, a researcher at the Swedish University of Agricultural Sciences.

“I think it may be that more perch benefit the pike because they are better at keeping the stickleback in check. However, we have not investigated this, so it is only a matter of speculation. We know that perch growth has increased due to increased food supply and rising temperatures. This may contribute to suppressing the stickleback. We are currently investigating these mechanisms”, he says.

The researcher also points out that improvements have only been seen in the inner archipelago.

“In the middle and outer archipelago, we have not found any improvements so far. There, sticklebacks have taken over and in many areas have wiped out the local populations of predatory fish,” says Ulf Bergström.

Henrik C. Andersson notes the same thing.
“The pike is basically gone there,” he says.

Uncertain

Joakim Hansen, environmental analyst at Stockholm University, believes it is too early to draw any conclusions about the possible causes of the test fishing results – or whether the pike population in the inner archipelago has even increased.

“We shouldn’t jump to conclusions; we first need to look at several factors. What was the weather like? How did the temperature develop during the spring? When did the ice melt? These things need to be analyzed. My answer is simply that it requires further research,” says Joakim Hansen.

“However, it is not impossible that the number of pike has increased.”

He also points out that smelt seems to have declined in recent years, that fishing pressure in the open sea off the Svealand coast is somewhat lower, and that it is logical that more protected archipelago areas give pike greater opportunity to increase in number.

^{About Deep Sea Reporter: Our ambition is to examine and report on issues related to the sea and the life that exists beneath its surface. We operate in the public interest and are independent of political, commercial, and other interests in society.}