Is a mandatory reporter required to report suspected abuse and neglect by law?

If mandatory reporting laws are "on the books" in the state/country/province you live in, then yes, they are. Mandatory reporting laws and their requirements can vary by location, but in general, they require certain professionals to report to law enforcement officials when they are aware that someone is harming or being harmed by another person. Requirements can also cover risk of harm.

Note: In the US, all professionals are mandatory reporters. This includes doctors, nurses, and public health and safety persons.