Final answer:
The decrease in the great white shark population can lead to an increase in the ray population, which can predate on bivalves, potentially contributing to further declines of oyster populations, already affected by human activities like overharvesting and environmental degradation.
Step-by-step explanation:
When the great white shark population decreased in North American coastal waters, it is believed that the ray population increased. Great white sharks are apex predators, and their decline would disrupt the trophic cascade, potentially leading to an increase in populations of prey species such as various rays. These rays, in turn, are known to feed on bivalves such as scallops, clams, and oysters. The increased predation pressure from rays could thus negatively impact the populations of these bivalves, possibly leading to decreased abundance.
Historically, oyster populations such as those in Chesapeake Bay have been significantly impacted not just by changes in predation but also by human activities including overharvesting and environmental degradation from fertilizer runoff and dead zones. These factors have critically reduced oyster reefs, from 200,000 acres in the 1700s to just 36,000 acres, affecting the ecosystem and its services.
The effect on oyster populations due to decreased shark numbers would not lead to an increase but might instead contribute to further declines because of a complex interplay of factors, including increased predation by other species that sharks would normally help keep in check.