Floating objects were evaluated as fish attractants in the offshore waters of Costa Rica. Flat plastic sheets were suspended vertically in the water and floated horizontally at the water surface. Sheets that floated on the water surface attracted more fish than those suspended vertically if they had equal surface area submerged. If the outside dimensions of the objects were equal no differences existed. The most fish were attracted to a plastic sheet bent at a 60° angle at its midline so that it resembled a small tent which floated with both sides submerged.
Aggregations were dominated initially by small juvenile fishes but after about 20 days by larger juveniles and adults. Tagged fish remained near moored objects from 8 days for Lobotes pacificus to over 32 days for Sectator ocyurus. Estimates of residency were 11–13 days for untagged yellowfin tuna, Thunnus albacares, and 9 days for black skipjack tuna, Euthynnus Hneatus.