Can you keep a spanish mackerel in Maryland?

14 inches, 15 a day, open all year. Same rule in the Chesapeake Bay and the Atlantic and coastal bays.

MD DNR source page

What we left out on purpose

• This page covers Maryland's tidal, estuarine and Atlantic species only. Maryland also regulates largemouth and smallmouth bass, walleye, yellow perch, chain pickerel and catfish in the same Chesapeake Bay and Tributaries table — those are freshwater and tidal-freshwater rules, out of scope for a silo that otherwise compares coastal species across states, and are not carried here.
• American lobster is left out. Maryland measures it by carapace length (3⅜ to 5¼ inches), a method this schema does not carry — every other species here is measured by total length.
• Grouper and snapper are published as combined, aggregate limits across every species in each group, exactly as Maryland's own table does — not broken out species by species.
• Where a species carries the identical rule on both the Chesapeake Bay and the Atlantic Ocean pages published by MD DNR, it is carried here once as 'statewide tidal waters' rather than as two duplicate regions.
• Sharks and tilefish are referenced by MD DNR's own tables as having further specialized regulations elsewhere; neither is carried here.