The bloodletting has begun.

Next week is the beginning of television networks’ annual upfront presentations, where they wine, dine and charm advertisers in hopes of enticing them to buy time for their fall offerings. For the rest of us, the events give a first look at which new and returning series the networks and cable channels will show this fall.

Which also means learning which shows won’t be back.

So it went on Thursday, when networks took the ax to a dozen series, from newcomers both acclaimed (“The Grinder”) and unloved (“Bordertown”) by critics, to fan favorites like “Castle, “Agent Carter” and “Nashville.” Another popular new show, “Supergirl,” will move from CBS to CW, and, after more than 15 years, the “CSI” era was officially closed after the demise of “CSI: Cyber,” the show’s remaining spinoff.