Monthly Archives: February 2012

Lake Victoria and the Nile Perch

The Nile perch (Lates niloticus) is a large, freshwater fish that provides a classic example of the dangers of invasive species. Introduced to Lake Victoria in the 1950’s, the Nile perch can weigh up to 200kg , and is highly valuable to the fishing industry for both food and sport fishing. Problems arose when the carnivorous fishes diet led to extensive predation of endemic cichlid species.

Covering over 68,000km2, Lake Victoria is the largest tropical lake in the world, which supports a diverse community of several hundred endemic cichlid species. In just 60 years, approximately half of the lakes cichlid have become extinct, from an original 400 estimated species to a current estimate of just 200. Upon introduction, Nile perch first fed on the abundant cichlid supply, but in recent years have moved towards a shrimp and minnow diet as a result of the decline. Overall populations have seen a dramatic decline, cichlids, which used to make up 80% of the fish biomass, now comprise just 1%.

The Nile Perch, D. Admassu

This rapid ecological impact would be alarming in any ecosystem, however it is of particular importance in this case for several reasons. Firstly, the cichlid speciation in Lake Victoria is very young with little genetic diversity, increasing the chances of substantial losses in genetic diversity and the Allee effect. The species found here are endemic, not occurring anywhere else in the world, and thus would be unrecoverable if they become extinct in this single body of water. Finally, this problem has developed in a very short time, with no natural mechanisms to prevent further damage. Further complexities are added by the commercial value of sustaining the Nile perch population, eutrophication due to sewage disposal in the lake depleting food supplies for cichlids, and local fisheries being outcompeted.

In response to the growing problems at Lake Victoria, there have been some attempts to aid the situation. Researchers have begun captive breeding of some of the cichlid species, funded by the IUCN. The Lake Victoria Research Team continue to investigate and monitor the lakes ecology and the threats to its wildlife. Conservation laws, such as fines for dumping sewage, have been established, particularly in Kenya, however conservationists must monitor both the implementation and effectiveness of these laws. OSIENALA, an NGO consisting of local communities that use the lake, was founded in 1992, and has helped local education about the lakes ecology whilst supporting the local community.

There are many challenges facing Lake Victoria, the Nile Perch has already had a major impact on the lakes unique ecology, but the problems are furthered by the key role of the lake in many peoples livelihood. Despite the problems, local and international efforts to target the threats and protect both ecology and the surrounding culture make a suitable starting point in protecting this highly threatened ecosystem.

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Conservation vs. The Public: The Red Cockaded Woodpecker

Endemic to the US, red cockaded woodpeckers (Picoides borealis) were once common throughout the south-eastern United States, but numbers rapidly fell following European settlement and subsequent habitat loss. Unlike most woodpecker species, the red cockaded woodpecker nests exclusively in living trees. Cavities are excavated for nesting, which can take up to 3 years, with most new colonisation occurring through reoccupation of old, abandoned sites, and competition for nesting cavities high.

Problems arouse between conservationists and landowners as a result of terms in the Endangered Species Act (ESA). The ESA states that ‘taking’ of protected species includes intentional or unintentional acts that harms or harasses that species, and can result in criminal prosecution. This means that any harm to a red cockaded woodpecker that occurs on a persons private property can be punished. Landowners are prevented from harvesting not only trees in which the woodpeckers reside, but surrounding trees, unable to change any of the surrounding habitat, and required to pay tax on the land’s previous value. As a result, preemptive habitat destruction began to occur in areas suited to red cockaded woodpeckers. Landowners harvested trees at younger stages, planted shortleaf pine over longleaf, and let understories grow.

The Red Cockaded Woodpecker, Rolf Nussbaum

The changes did not go unnoticed by conservationists. Following a surge of conservation laws in the 1970’s, alterations to reduce public resentment whist still protecting the environment have been a high priority. Today, plans such as ‘safe harbour’ and ‘no surprises’ policies allow landowners to set use their land as they wish with no repercussions if they set aside some areas for threatened species. The public is encouraged to involve themselves in ecological issues, and negative impacts of conservation investigated before conservation plans are drawn up. Although still threatened, red cockaded woodpeckers are today considered only ‘vulnerable’ by researchers, due to conservation efforts.

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