Hammerhead sharks and tunas are both kinds of fish. Most sharks live in the tropics. Most shark attacks occur on boats. The largest sharks eat microplankton. Dogfish Sharks can rest on the seafloor so long as a strong current moves by their gills.
Sharks have a blood salinity closer to freshwater than do salmon.
Sharks expend a great deal of energy parenting. Both Great Whites and Hammerhead Sharks have attacked humans. Sharks have a lousy sense of smell.