No one would blame you for thinking of canned sardines as little more than a Depression-era, protein-packed pantry staple (or the craving of cartoon cats). But the silvery swimmers—whether packed in spring water, olive oil or tomato purée—are enjoying a culinary boom.

Credit for the surge may go to sardine-promoting chefs like Seamus Mullen, of New York's Tertulia, who likes to snack on flavorful fillets piled onto a halved, mayonnaise-smeared baguette with sliced cucumber, grated carrots and cilantro.

Ethan...