Two male Hawaiian monk seals (Monachus schauinslandi) at French Frigate Shoals in the northwestern Hawaiian Islands. Monk seals are the only true seals found year-round in tropical waters. They are found on coral atolls and rocky islands. The seal on the right bears a temporary bleach mark that was placed to help determine abundance through a mark-recapture technique. Mark-recapture methods are used to estimate population size and other parameters by marking a known number of individuals and then counting the number that are recaptured. This photograph originally appeared on the cover of Ecological Applications (14:4) in August of 2004.