Evaluation of Rectangular and Circular Escape Vents in the Northwestern Hawaiian Islands Lobster Fishery

Research was conducted in Hawaii during 1984–1987 to investigate the possibility that escape vents fitted in traps used by the commercial lobster fishery in the northwestern Hawaiian Islands would reduce the catch and mortality of sublegal spiny lobsters Panulirus marginatus (<50 mm tail width) and slipper lobsters Scyllarides spp. (<56 mm tail width) without significantly reducing legal catch. A circular vent was more efficient than the traditional rectangular vent in maximizing escapement of sublegal lobsters and retention of legal ones for both species. Optimum results were attained with two vented panels each containing four 67‐mm‐diameter circular vents. Traps equipped with the circular vents caught 83% fewer sublegal spiny lobsters and 93% fewer sublegal slipper lobsters than nonvented control traps, and they did not significantly reduce legal catch of either species. In contrast, traps with two 49‐mm‐high × 285‐mm‐wide rectangular vents reduced the catch of sublegal spiny and slipper lobsters by 70 and 93%, respectively, but also reduced legal slipper lobster retention by a significant 32% of the control catch. As a result of this research, all traps used in the lobster fishery in the northwestern Hawaiian Islands after l January 1988 must be equipped with two panels with 67‐mm circular vents. The 1988 catch of sublegal spiny lobsters declined by 38% at Necker Island, northwestern Hawaiian Islands, whereas the legal catch increased substantially.