Final answer:
Shellfish identification tags must be kept for at least 90 days to help trace the source in case of foodborne illness, ensuring public health and safety.
Step-by-step explanation:
Shellfish identification tags must be kept for a minimum of 90 days after the shellfish have been used or sold.
This regulation is in place for public health and safety reasons, to ensure that if there is a case of foodborne illness, there is a means to trace back to the source of the shellfish.
By maintaining these records, businesses can assist health departments in identifying the source of contaminants and take necessary action to prevent further cases.