Answer: B - The average body size of the salmon population decreased significantly.
Starting in 1954, when commercial fishers in the northwest Pacific were paid by weight rather than by the individual fish for pink salmon, they increased the use of a type of net that selectively catches larger fish. This change in fishing method would lead to a decrease in the average size of fish because of the phenomenon known as fishing down the food web.
Fishing down the food web refers to the tendency for fishing pressure to shift from larger, higher trophic level species to smaller, lower trophic level species over time. This occurs because larger, more valuable species and individuals of specials become depleted. To make up for this fishers target smaller, less valuable species to maintain their catch. In this case, by using a type of net that selectively catches larger fish, the fishers are removing the larger individuals from the population, leading to a decrease in the average size of the fish.
Moreover, by removing the larger individuals, the fishers are also changing the structure of the population, altering the balance of size classes and disrupting the natural size distribution of the species leaving more resources for smaller fish and genetically selecting out larger ones. This can have negative impacts on the population and its ecosystem, leading to declines in biodiversity, reductions in biomass, and changes in the food web structure.
