The Rescue Effect by Michael Mehta Webster

Author:Michael Mehta Webster
Language: eng
Format: epub
Publisher: Timber Press
Published: 2022-06-15T00:00:00+00:00

A Series of Unfortunate Events

In the 1980s, in the midst of the scientific efforts to understand how the Lake Victoria cichlid diversity came to be, species started to disappear and fisheries for the haplochromines started to collapse. It was as though someone was firing a shotgun into the species flock, leaving only a very few survivors. What was causing the downfall of the haplochromines? Those who study Lake Victoria have a short version and a long version of the answer. The short version is that a giant predatory fish, the Nile perch, was deliberately introduced to the lake, and it gobbled up the haplochromines so fast that it overwhelmed the rescue effect for hundreds of species. The long version adds that, at the same time that the Nile perch were ascending, a host of other changes were also underway.

As its name suggests, the Nile perch is native to the Nile River in northern Africa; it’s also found in many other freshwater rivers and lakes in northern and western Africa. It resembles a bass or a snapper—but super sized. The largest individuals can grow to almost 6 feet (2 m) long and can weigh as much as 440 pounds (200 kg), which is about the size of an adult male African lion. The Nile perch is also notable for its huge, suction-powered jaws, which help it swallow fish whole.

Although Lake Victoria is one of the sources of the Nile River, Nile perch were historically confined to the lower parts of the river by barriers such as waterfalls that kept them from swimming upstream to the lake. However, in the first half of the twentieth century, existing fisheries in Lake Victoria were deemed by British colonial leaders to be underperforming economically. They debated “whether fishery productivity might be increased by introducing non-indigenous species to Lake Victoria.” Most of the fish being harvested were small and not suitable for markets outside of local communities. The idea was that, by introducing a large species of fish to the lake, the small fish—including the haplochromine cichlids—could support something more valuable: a harvestable fish with desirable flaky, white filets that could be sold commercially. Nile perch was an obvious choice for introduction, because it was already present in other parts of Africa and it could grow to enormous sizes. For those promoting the introduction of Nile perch, the possible negative effects on haplochromine cichlids were of little to no concern. To them, the haplochromines were small “‘trash fish’ of very little value.”

Not everyone saw the proposed introduction of Nile perch as a good idea, however. Some fisheries biologists who were studying the lake worried that the species introduction could have unintended consequences and might not achieve the purported benefits. For example, in 1960, Geoffrey Fryer of the East African Fisheries Research Organization in Uganda argued that the rationale for introducing Nile perch to increase lake productivity was “based on ignorance of several fundamental biological concepts.” The most notable concern was that the Nile perch would consume too many of the small fish, which were a potential food source for local communities.

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