Final answer:
The biggest challenges to Lake Titicaca's fisheries are overfishing, leading to the overexploitation of fish populations, and invasive species, which disrupt the native ecosystem and compete with indigenous species.
Step-by-step explanation:
The most significant threats to the fisheries in Lake Titicaca are overfishing and invasive species. Overfishing can decimate the populations of native fish species. For example, the western Atlantic cod fishery collapsed due to the introduction of modern factory trawlers in the 1980s, leading to unsustainable harvesting rates. This phenomenon, often a result of the 'tragedy of the commons,' occurs when multiple fishers harvest fish without coordinated efforts to preserve the population, leading to overexploitation.
Invasive species are another major threat as they can alter native ecosystems, compete with indigenous fauna for resources, and potentially introduce diseases. The changes they bring can result in further stress for native species and ecosystems, which may struggle to adapt to the new conditions imposed by these non-native organisms. Considering these factors, the most correct answer to the question regarding the biggest challenges to Titicaca's fisheries would be B) Overfishing and invasive species.