The Vanishing Fish of Lake Sevan
Lake Sevan, Armenia's largest freshwater body, has experienced a dramatic decline in its endemic fish population, particularly the Sevan trout (Salmo ischchan). In the 1980s, commercial catches averaged 1,200 tons per year. By 2020, the catch had fallen to less than 50 tons. Scientists attribute the decline to multiple factors: water level reduction due to hydroelectric power generation and irrigation, pollution from agricultural runoff, and the introduction of non-native species such as the whitefish (Coregonus lavaretus). The Armenian government has implemented a fishing ban during spawning season and hatchery programs to restock the lake. However, local fishermen argue that the ban threatens their livelihoods, and enforcement is weak due to limited resources.
1. Identify two ecological factors and one socio-economic factor contributing to the decline of the Sevan trout. Explain how each factor interacts with the others to exacerbate the problem.
Read the worked answer
Ecological factors: (1) Water level reduction: Lower water levels shrink spawning grounds and increase water temperature, reducing oxygen levels and stressing trout. (2) Introduction of non-native whitefish: Whitefish compete with trout for food (zooplankton and benthic organisms) and may prey on trout eggs. Socio-economic factor: Weak enforcement of fishing bans due to limited resources and the need for local livelihoods. Interaction: Water level reduction (driven by hydroelectric and irrigation demands) concentrates pollutants and reduces habitat, making trout more vulnerable to competition from whitefish. Meanwhile, economic hardship leads to illegal fishing, further depleting the already stressed population. This creates a feedback loop: as fish become scarcer, illegal fishing intensifies, and enforcement is undermined by the same economic pressures.
2. Evaluate the effectiveness of the government's two measures (spawning-season ban and hatchery restocking) in addressing the decline. Propose one additional measure that could improve outcomes, justifying it with ecological and social reasoning.
Read the worked answer
The spawning-season ban is theoretically effective because it protects fish during reproduction, allowing populations to recover. However, weak enforcement limits its impact, as illegal fishing continues. Hatchery restocking can boost numbers, but if habitat conditions (water level, pollution, competition) are not improved, stocked fish may not survive. Moreover, hatchery fish may have lower genetic diversity, reducing resilience. An additional measure could be integrated water resource management: adjusting water releases from reservoirs to maintain higher lake levels during critical spawning periods. This would require coordination between energy, agriculture, and environmental agencies. Ecologically, higher water levels improve spawning habitat and water quality. Socially, it could be paired with alternative livelihood programs for fishermen (e.g., eco-tourism or aquaculture) to reduce pressure on wild stocks. This measure addresses root causes rather than symptoms.