Wildlife watch: the stickleback

A few years ago as I was walking in the valley of a river near where I live I came across some pools which had been created by flooding in the winter but were now starting to dry out in the spring. I decided to have a closer look and discovered lots of tadpoles and a surprising number of small fish.

They were all trapped in a small muddy pool and were destined to perish so I decided to rescue as many as I could. With a net I scooped out water which wriggled with life and I transferred it to a large, permanent pool nearby. Having taken a closer look at the fish I found they were sticklebacks so I decided to take a few to put into my wildlife pond, a short distance away.*

My garden pond is targeted at wildlife. Around it I let the vegetation grow tall and within it I plant only native species. It has become a magnet for dragonflies and we have frogs and toads spawning most years. I wouldn’t ever consider introducing non-native fish because they create an imbalance. Species such as koi carp grow large and eat a lot, they inevitably eat the tadpoles and dragonfly larvae leaving the pond devoid of natural life. However, I was happy to provide a home for a few sticklebacks which are most-definitely native.

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UK native stickleback species

In fact there are three stickleback species in the UK. They are identified by the number of spines on their backs: three-spined; nine-spined and fifteen-spined sticklebacks. The fifteen-spined is purely marine, the nine-spined can be marine or freshwater but the ones I had come across were the three-spined, our commonest freshwater stickleback.

Despite its name the three-spined stickleback doesn’t always exhibit three clear spines along it back, some can have four and others just two. But all of them are very small, with the largest individuals no more than seven centimetres long.

Three-spined stickleback female, photographed by David Chapman

Observing sticklebacks

It's lovely to be able to see them, especially in spring when the males develop a striking blue eye and orange throat in preparation for their courtship. The clever male stickleback makes a nest at the bottom of the pond using pieces of plant held together with sticky threads which are ejected from his kidneys. Then, using his colourful attributes and a zigzag dance, he sets about attracting a female to lay eggs in his nest. After the eggs are laid the male will fertilise them and then, quite remarkably, he stands guard over the nest for about four weeks until the eggs hatch.

Sticklebacks are predators, so they will be eating a small number of tadpoles and other aquatic life, but they aren’t the top predators. We have been getting regular visits from a grey heron for the last couple of years and I’m sure that will be helping to keep nature in balance. We have also had an otter visit occasionally, though I can only tell this because of the spraints that it leaves behind. I am yet to see kingfishers, something that continues to disappoint me, but I imagine a stickleback will make a tasty snack when they eventually pop by.

Three or four years after the introduction we still have sticklebacks in our pond, though I can go for months without seeing them. I don’t attempt to feed them because this would serve to increase their population to an artificially high level which might create a negative imbalance in the ecosystem. It is difficult to estimate their population from my brief sightings, but it is clear that initially they increased in number and then dipped a little before remaining fairly stable. This is good news because it indicates they have formed an equilibrium with the rest of the wildlife using the pond, which is not really a surprise since sticklebacks belong here.

*Transferring creatures or vegetation from one watercourse to another is not a good idea because there is a danger of transferring unwanted weeds or even disease with them but since this was very close to my own pond, just a little further down the same river, I thought the risk was minimal.

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