The concept of Pokemon being food, whether it be for humans or other Pokemon, has always been something fans have assumed, but has been rarely acknowledged by the games. There have certainly been occasional implications (for example, Slowpoke tails are used as a curry ingredient in Pokemon Sword and Shield), but while it's safe to assume that Nintendo and Game Freak will never show a Pokemon being eaten on-screen, New Pokemon Snap seems to have no qualms with at least heavily suggesting it.
One of the official Pokemon Twitter accounts shared a short clip of New Pokemon Snap footage, which is releasing at the end of the month, and while it doesn't reveal any major new info about the game, it does show two poor Magikarps being taken away by other Pokemon, heavily implying that they've been captured as prey to be eaten. The first instance shows a Magikarp splashing in shallow water before suddenly being swept up by a Pidgeot, holding the fish in its talons, which perfectly mirrors how some real-world birds catch fish.
This is also a blatant reference to some of Pidgeot's PokeDex entries. The original Red and Blue games state that it skims the surface of the water to pick off prey, with Magikarp given as a specific example. This is reiterated in other games like Pokemon X and Y.
The second scene shows a Magikarp, instead of being taken skyward, dragged deeper into the ocean by a Frillish, a Water/Ghost type. Just like Pidgeot, Frillish's own PokeDex entry in multiple games mentions how it uses its arms to drag prey into the ocean depths, while also using a poison to paralyze them. With this knowledge in mind, it's pretty clear what became of these Magikarps.
It's a surprisingly dark aspect to include in a game as colorful and cartoony as the Pokemon series, but it does fit with the general conceit of New Pokemon Snap. Players take on the role of a wildlife photographer to study how Pokemon act in the wild so it makes sense to witness demonstrations of the Pokemon food chain, even if the game won't actually show it.
It does beg the question whether any other Pokemon will be depicted as prey as well or if it's limited to just Magikarp. There are arguably plenty other Pokemon that could be targeted by Pidgeots and Frillish, namely other fish-like Pokemon such as Finneon or Feebas, but it arguably makes sense for it to just be Magikarp given its status as a joke Pokemon. In the main games, Magikarp is mostly useless in battle, only ever used by players so it can be evolved into a Gyarados.
New Pokemon Snap releases for Nintendo Switch on April 30th.