The experiment

Northern pike (Esox lucius) is a large apex predator that naturally occurs in most parts of Alaska, except south and east of the Alaska Mountain Range. Due to illegal stocking activities by humans, northern pike has spread to lake systems beyond its natural range. Recent introductions of pike in Southcentral Alaska has led to significant declines in many other fish species, including salmonids, as fish that have evolved in the absence of pike are highly susceptible to pike predation. Due to its negative environmental impacts, the northern pike is considered an invasive species. In order to prevent the spread, the Alaska Department of Fish & Game (ADFG) has taken measures to eradicate pike. In 2018, ADFG treated a lake system consisting of eight lakes in the Kenai Peninsula using rotenone. Rotenone is one of the few efficient methods for eradicating invasive fish, but requires restocking of all naturally occurring species post-treatment.

 Threespine stickleback (Gasterosteus aculeatus) is a naturally occurring species of fish in Southcentral Alaskan lakes. It has an important position in the food web and acts as a significant food source for both birds and larger predatory fish, such as salmonids. It is also an interesting model organism for research. Sticklebacks are abundant across the northern hemisphere and have shown to be extremely adaptable to different types of habitats ranging from marine environments to freshwater streams and lakes. 

 Being a naturally occurring fish species in Alaska, sticklebacks play a central role in supporting a healthy ecosystem and they have an important part in lake restoration.

In 2019, we collected three-spined sticklebacks from eight different source populations from lakes in the Mat-Su region and the Kenai Peninsula. Half of the source population lakes corresponded to a typical limnetic habitat and half of the lakes had the characteristics of a benthic habitat. The fish from different populations were pooled into multiple batches to create an experimental design where each of the eight empty rotenone-treated lakes received a mixture of benthic or limnetic sticklebacks from different source populations. We also restocked a ninth lake that had been rotenoned in 2017 with sticklebacks from all source populations. A total of approximately 10000 individual fish were collected, photographed and fin clipped prior to being released into their new habitat. This will allow us to study the genomics and morphology of the ancestral populations and to track how they change over time. 

The reintroduction efforts were successful in all lakes apart from one lake that we restocked with sticklebacks from seven different source populations in 2022.